My new ride..an old 720

[kilohertz]

Hi gang, New here, but old in many other ways. Finally, after a 2 year search for a skidsteer, I found a Clark 720 in pretty decent condition. It runs, but only on 3 cylinders. One cylinder has little to no compression. I just got it home last night so I haven't had time to investigate but it can really only be a couple of things. Rings, valves or hole in the piston. It quit on him about 3 years ago with a backfire and a loud bang. He managed to get it parked and there it sat for 3 years until I rescued it. It came with the original owners and service manual, as well as a spare, weathered, siezed spare engine, not sure what value it has but may have some usable internal parts. Once I figure out how to post pics, I'll do so. Cheers Paul

 

[flyerdan]

If you're lucky it could also be a head gasket. Mine had one go out years ago, made a chirping whistle sound. If that's the case it's a cheap and easy fix; here's hoping. They are a nice size for an around the house plaything, can get in a lot of areas and still do a fair amount of work.

 

[kilohertz]

If you're lucky it could also be a head gasket. Mine had one go out years ago, made a chirping whistle sound. If that's the case it's a cheap and easy fix; here's hoping. They are a nice size for an around the house plaything, can get in a lot of areas and still do a fair amount of work.

Well woooo bloody hoooo!! I started tearing it apart at 1:30 today, thought I better start with the simple things, so did a compression test and found the bad cylinder. 0 PSI, other 3 were 90 PSI. Removed the sheet metal on the left bank and the manifold/carb. Thought I better check the simple things first, so I pulled the tappet/valve adjuster cover and woo hooo! It was just a stuck exhaust valve!! Sprayed some pentrating oil around the stem and popped it free with a screwdriver, worked it a little bit, then turned it over with the starter to make sure it wasn't going to stick again and put it all back together. Drove it off the flatdeck trailer at 6pm and drove it around the yard....works great!! Hydraulics are tight and snappy, tranny sounds good. Now I need to go through the maintenance schedule and change fluids etc and then give it a good workout. I'll keep you posted. I sure got lucky with this one. Cheers Paul

 

[Tazza]

Well woooo bloody hoooo!! I started tearing it apart at 1:30 today, thought I better start with the simple things, so did a compression test and found the bad cylinder. 0 PSI, other 3 were 90 PSI. Removed the sheet metal on the left bank and the manifold/carb. Thought I better check the simple things first, so I pulled the tappet/valve adjuster cover and woo hooo! It was just a stuck exhaust valve!! Sprayed some pentrating oil around the stem and popped it free with a screwdriver, worked it a little bit, then turned it over with the starter to make sure it wasn't going to stick again and put it all back together. Drove it off the flatdeck trailer at 6pm and drove it around the yard....works great!! Hydraulics are tight and snappy, tranny sounds good. Now I need to go through the maintenance schedule and change fluids etc and then give it a good workout. I'll keep you posted. I sure got lucky with this one. Cheers Paul

Wow, you did really well.
Give it a good flogging then change the oil.
Surprised it started on 90 PSI, i thought they mostly need 180 psi or so, good news all the same, so simple too.

 

[kilohertz]

Wow, you did really well.
Give it a good flogging then change the oil.
Surprised it started on 90 PSI, i thought they mostly need 180 psi or so, good news all the same, so simple too.

Hi Tazza, Yes, that's my plan. I put in a little ATF and Wynn's tune up to free up things. I'll run it for a while then do the change and load it with fresh 15/40. Now, I have another question. I have looked through the service and owner's manuals and can't quite figure out if there is one or two oil resevoirs for the hydraulics and hydrostatic drive. The books say you can use 10-30 or 15-40 oil instead of the Clark oil but I have never heard of using 10-30 in hydraulics. I can only see reference to one hydraulic filler, the plug on the left side of the frame, to fill hydraulics. Could you clarify for me, what fluids this beast needs and where to add them. Cheers Paul

 

[flyerdan]

Hi Tazza, Yes, that's my plan. I put in a little ATF and Wynn's tune up to free up things. I'll run it for a while then do the change and load it with fresh 15/40. Now, I have another question. I have looked through the service and owner's manuals and can't quite figure out if there is one or two oil resevoirs for the hydraulics and hydrostatic drive. The books say you can use 10-30 or 15-40 oil instead of the Clark oil but I have never heard of using 10-30 in hydraulics. I can only see reference to one hydraulic filler, the plug on the left side of the frame, to fill hydraulics. Could you clarify for me, what fluids this beast needs and where to add them. Cheers Paul

There should be a real filler tube in the engine compartment like in the picture. The 1/4" plugs on the side are for level checks, it would take a long time to fill using them. The drive and lift share the same system, mine had hydraulic fluid in it so that's what I use. We did have a 743 at work that used 10W30 for hydraulic oil, but it was quite a bit newer.

Hydraulic fill is opposite the fuel fill on mine

 

[Tazza]

There should be a real filler tube in the engine compartment like in the picture. The 1/4" plugs on the side are for level checks, it would take a long time to fill using them. The drive and lift share the same system, mine had hydraulic fluid in it so that's what I use. We did have a 743 at work that used 10W30 for hydraulic oil, but it was quite a bit newer.

Hydraulic fill is opposite the fuel fill on mine

They use heavier oil for hydrostatic transmissions. It needs to be thicker to keep lubricating the pumps. Stick with the ehavier weight oil, i thought the same when i bought my first machine, a 731. The seller told me it ran engine oil, i thought i knew what was causing the problem that was the reason it was being sold, turns out the oil was right, it was a plugged filter.

 

[kilohertz]

They use heavier oil for hydrostatic transmissions. It needs to be thicker to keep lubricating the pumps. Stick with the ehavier weight oil, i thought the same when i bought my first machine, a 731. The seller told me it ran engine oil, i thought i knew what was causing the problem that was the reason it was being sold, turns out the oil was right, it was a plugged filter.

Hi Tazza, FlyerDan, Thanks for the replies. Well, my oil resevoir hole is right at the top of the tank on the left side, has a 1" pipe thread plug in it, right in the drivers compartment. Nothing like your fancy tube beside the engine. Okay on the oil weight. I will drain some and figure out what is in there, then top off as required with the same. My biggest concern right now is, after running around the yard today, I find the engine is bogging down when moving forward at high speed. Bucket and lift arm functions are quick and snappy but when I try to move forward at full speed, either low or high range, it drags the engine down severly, almost stalling. I put in new spark plugs and will change out wires, points condensor in the next day or so and report back. I cleaned out the carb and set the governor spring in the 11th hole. Haven't checked compression again since I got it running but suspect it still to be about 90 PSI. any thoughts on this new development? Cheers for now and thanks for the help. Paul

 

[Tazza]

Hi Tazza, FlyerDan, Thanks for the replies. Well, my oil resevoir hole is right at the top of the tank on the left side, has a 1" pipe thread plug in it, right in the drivers compartment. Nothing like your fancy tube beside the engine. Okay on the oil weight. I will drain some and figure out what is in there, then top off as required with the same. My biggest concern right now is, after running around the yard today, I find the engine is bogging down when moving forward at high speed. Bucket and lift arm functions are quick and snappy but when I try to move forward at full speed, either low or high range, it drags the engine down severly, almost stalling. I put in new spark plugs and will change out wires, points condensor in the next day or so and report back. I cleaned out the carb and set the governor spring in the 11th hole. Haven't checked compression again since I got it running but suspect it still to be about 90 PSI. any thoughts on this new development? Cheers for now and thanks for the help. Paul

At full speed it will bog down a fair bit if you just try and throw the sticks forward. If you get it up there fast, but not instantly it shouldn't stall.
I'd start with ignition, check the carb that its ok, fuel filters/lines then look at the govenor. I think they have their own oil, if its not changed in a while or leak they can lock up. It would explain the bogging down under load. The drive will use the most HP, the lift/tilt will only use a little, that's why it still lifts easily and fast.
How does it start? does it take some work?

 

[kilohertz]

At full speed it will bog down a fair bit if you just try and throw the sticks forward. If you get it up there fast, but not instantly it shouldn't stall.
I'd start with ignition, check the carb that its ok, fuel filters/lines then look at the govenor. I think they have their own oil, if its not changed in a while or leak they can lock up. It would explain the bogging down under load. The drive will use the most HP, the lift/tilt will only use a little, that's why it still lifts easily and fast.
How does it start? does it take some work?

Well, a little news to report. First, I figured out how to post HTML and get the proper spacing in my paragraphs, which has all been jammed up into one paragraph.
Test.
So I finally found all the ignition parts today at our local NAPA. I have only changed the cap and rotor so far as I ran out of daylight. The points and condenser look shiney new so I am going to leave those. I have new plug wires to install tomorrow. The cap/rotor got rid of the little bit off random popping and she runs smoother but stills bogs right down to a stall when trying to get up to full speed, even easing into it. I have cleaned out the carb and installed an externally mounted replaceable canister style fuel filter. She starts right up quick and runs under no load just fine.
I have several things still to do as I found tonight, when I replaced the cap, that someone over the years has rotated the distributor 90 degrees and I had a hard time getting it going again and had to fall back to finger in #1 and watch the rotor trick to find #1 on the rotor. Runs great now. So, remaining after changing the wires is to check the advance weights, check the timing and now, thanks Tazza, find out where to check the govenor oil and change that out. The machine sat outside in the sun and weather for the last 4 years, so who knows what needs to be replaced or checked.
I am pleased with what I found buried in the service manual...some receipts for work done in the last 12 years. The whole engine was rebuilt in 1998 at 200 hours indicated, as it had spun a bearing. Was bored .030 over and .010 under on the crank. $3790 worth of work. Then in 2003 at 900 hours indicated, all drive chains were changed and whatever else was needed, remove and flush the gas tank, etc to the tune of $3000 and now it has 1390 hours indicated so there are just over 1000 hours on the rebuilt engine. I don't know how that rates in machine world, is it low or high? Seems pretty low to me. I'm guessing the clock has gone around once.
Once I get the engine running right, I will dive into the maintenance side of the hydraulics.
I think that's it for now.
Thanks again!!
Paul

 

[Tazza]

Well, a little news to report. First, I figured out how to post HTML and get the proper spacing in my paragraphs, which has all been jammed up into one paragraph.
Test.
So I finally found all the ignition parts today at our local NAPA. I have only changed the cap and rotor so far as I ran out of daylight. The points and condenser look shiney new so I am going to leave those. I have new plug wires to install tomorrow. The cap/rotor got rid of the little bit off random popping and she runs smoother but stills bogs right down to a stall when trying to get up to full speed, even easing into it. I have cleaned out the carb and installed an externally mounted replaceable canister style fuel filter. She starts right up quick and runs under no load just fine.
I have several things still to do as I found tonight, when I replaced the cap, that someone over the years has rotated the distributor 90 degrees and I had a hard time getting it going again and had to fall back to finger in #1 and watch the rotor trick to find #1 on the rotor. Runs great now. So, remaining after changing the wires is to check the advance weights, check the timing and now, thanks Tazza, find out where to check the govenor oil and change that out. The machine sat outside in the sun and weather for the last 4 years, so who knows what needs to be replaced or checked.
I am pleased with what I found buried in the service manual...some receipts for work done in the last 12 years. The whole engine was rebuilt in 1998 at 200 hours indicated, as it had spun a bearing. Was bored .030 over and .010 under on the crank. $3790 worth of work. Then in 2003 at 900 hours indicated, all drive chains were changed and whatever else was needed, remove and flush the gas tank, etc to the tune of $3000 and now it has 1390 hours indicated so there are just over 1000 hours on the rebuilt engine. I don't know how that rates in machine world, is it low or high? Seems pretty low to me. I'm guessing the clock has gone around once.
Once I get the engine running right, I will dive into the maintenance side of the hydraulics.
I think that's it for now.
Thanks again!!
Paul

1000 hours on a petrol engine isn't much, diesels generally do 6,000 before needing freshing up. So it seems to have a lot of life left in it.

 

[kilohertz]

1000 hours on a petrol engine isn't much, diesels generally do 6,000 before needing freshing up. So it seems to have a lot of life left in it.

Okay, well all new ignition high voltage side, timing correct, governor working fine, no improvement, so back to basics.
I decided to recheck compression on the original problem cylinder (#2) and found it was down to 20PSI when hot, the rest are about 75 when hot. The engine was running fine with light load and I played around the yard moving some snow into a pile for my son to play in. It ran fine. So now I know why it boggs down easily, one cylinder is basically dead.
So now.....I put a little ATF and MMO in the crank, same into the gas tank and ran it around for a little while then removed the pipe thread plug on the intake manifold and ran it at about 1500RPM then killed it with ATF into the intake. I will let it sit for a day or two and see if that does anything. The chambers were quite carboned and I pulled as much out with my fingers as I could, then blew out the chambers and put the valve cover back on when I got it running a few days back. So I know the valve is free but probably not seating properly. I put a tablespoon of oil in the cyclinder and rechecked with no improvement so I am going to assume the rings are still okay.
Question, will I damage anything by running it like it is for a while to see if the valves find their happy place again? I am hoping not to have to pull the head and valves, but it's not a big deal if I need to. I would rather just see if it fixes itself. Remember, this unit crapped out 4 years ago and the guy let it sit outisde for 4 years so it may need some time so run in again.
Your thoughts?
Cheers
Paul

 

[Tazza]

Okay, well all new ignition high voltage side, timing correct, governor working fine, no improvement, so back to basics.
I decided to recheck compression on the original problem cylinder (#2) and found it was down to 20PSI when hot, the rest are about 75 when hot. The engine was running fine with light load and I played around the yard moving some snow into a pile for my son to play in. It ran fine. So now I know why it boggs down easily, one cylinder is basically dead.
So now.....I put a little ATF and MMO in the crank, same into the gas tank and ran it around for a little while then removed the pipe thread plug on the intake manifold and ran it at about 1500RPM then killed it with ATF into the intake. I will let it sit for a day or two and see if that does anything. The chambers were quite carboned and I pulled as much out with my fingers as I could, then blew out the chambers and put the valve cover back on when I got it running a few days back. So I know the valve is free but probably not seating properly. I put a tablespoon of oil in the cyclinder and rechecked with no improvement so I am going to assume the rings are still okay.
Question, will I damage anything by running it like it is for a while to see if the valves find their happy place again? I am hoping not to have to pull the head and valves, but it's not a big deal if I need to. I would rather just see if it fixes itself. Remember, this unit crapped out 4 years ago and the guy let it sit outisde for 4 years so it may need some time so run in again.
Your thoughts?
Cheers
Paul

Hopefully its just chunks of carbon getting stuck under the valve as when you had the valve free the compression was constant across all cylinders.
Not sure if it will find its place in the head, valves are made to be able to rotate, so there is no garantee that it will always find its spot that seals correctly.

 

[kilohertz]

Hopefully its just chunks of carbon getting stuck under the valve as when you had the valve free the compression was constant across all cylinders.
Not sure if it will find its place in the head, valves are made to be able to rotate, so there is no garantee that it will always find its spot that seals correctly.

Hello all,
Well good news to report this time. I started it this morning and burned out all the ATF that was sitting in there then took it for a good ride around the yard and moved some more snow. I emptied the fuel filter of all the water that had collected in the last few days, will probably take a few tanks to get all of it out but once gone, will put in a new canister filter. I then put on a vacuum gauge to see what was going on and sure enough, I could see the needle swinging around like mad, indicated sticking valves. Then, I did some internet research about ATF and carbon and found lots of hot rod info from 50's-70's about cleaning combustion chambers without pulling the heads. There were many references to spraying small amounts of water and ATF into the carb while the engine is at about 2000 RPM, letting it sputter and loosen up the carbon and spit it out. So I rigeed up a vacuum hose to the hole on the intake and made up a mix of snow melted water and ATF , then let the engine drink it up slowly, took about 5 minutes to suck up 16 oz. It sputtered a few times while doing this and caught up then when it was done, I took it out for another spin with the vacuum gauge still attached and noticed a big improvement in the gauge reading and the the power the machine had. It continued to get better and by the time I quit, about 1/2 hour, I shut it down and checked the compression again and found it now to be 50PSI, big improvement from yesterday. So it's soaking in ATF again and will repeat this afternoon and that should have it!! Yeah.
I'll keep you posted.
Cheers
Paul

 

[flyerdan]

Hello all,
Well good news to report this time. I started it this morning and burned out all the ATF that was sitting in there then took it for a good ride around the yard and moved some more snow. I emptied the fuel filter of all the water that had collected in the last few days, will probably take a few tanks to get all of it out but once gone, will put in a new canister filter. I then put on a vacuum gauge to see what was going on and sure enough, I could see the needle swinging around like mad, indicated sticking valves. Then, I did some internet research about ATF and carbon and found lots of hot rod info from 50's-70's about cleaning combustion chambers without pulling the heads. There were many references to spraying small amounts of water and ATF into the carb while the engine is at about 2000 RPM, letting it sputter and loosen up the carbon and spit it out. So I rigeed up a vacuum hose to the hole on the intake and made up a mix of snow melted water and ATF , then let the engine drink it up slowly, took about 5 minutes to suck up 16 oz. It sputtered a few times while doing this and caught up then when it was done, I took it out for another spin with the vacuum gauge still attached and noticed a big improvement in the gauge reading and the the power the machine had. It continued to get better and by the time I quit, about 1/2 hour, I shut it down and checked the compression again and found it now to be 50PSI, big improvement from yesterday. So it's soaking in ATF again and will repeat this afternoon and that should have it!! Yeah.
I'll keep you posted.
Cheers
Paul

Glad to hear that it's a relatively simple problem that won't require a bunch of costly parts to fix. You might think about using Seafoam on it; if the ATF loosens it up enough to run consistantly a full Seafoam oil and fuel treatment should clean out even more.

 

[ZackaryMac]

Hello all,
Well good news to report this time. I started it this morning and burned out all the ATF that was sitting in there then took it for a good ride around the yard and moved some more snow. I emptied the fuel filter of all the water that had collected in the last few days, will probably take a few tanks to get all of it out but once gone, will put in a new canister filter. I then put on a vacuum gauge to see what was going on and sure enough, I could see the needle swinging around like mad, indicated sticking valves. Then, I did some internet research about ATF and carbon and found lots of hot rod info from 50's-70's about cleaning combustion chambers without pulling the heads. There were many references to spraying small amounts of water and ATF into the carb while the engine is at about 2000 RPM, letting it sputter and loosen up the carbon and spit it out. So I rigeed up a vacuum hose to the hole on the intake and made up a mix of snow melted water and ATF , then let the engine drink it up slowly, took about 5 minutes to suck up 16 oz. It sputtered a few times while doing this and caught up then when it was done, I took it out for another spin with the vacuum gauge still attached and noticed a big improvement in the gauge reading and the the power the machine had. It continued to get better and by the time I quit, about 1/2 hour, I shut it down and checked the compression again and found it now to be 50PSI, big improvement from yesterday. So it's soaking in ATF again and will repeat this afternoon and that should have it!! Yeah.
I'll keep you posted.
Cheers
Paul

Paul Are you checking your compression with the throttle wide open? Just wondering, as this is the way you are supposed to check it. You didn't make mention of it, so I thought I would ask. I work at a tractor shop, that also used to sell Thomas skid steers. The shop foreman, who has been there for 25 years, tell me they all used 10w-30 for the hydraulics, and it is common to use this (at least in our climate). My Case 1818 uses 10w-30 for shared hydraulics and drive. The chains are also lubed with it, but separately in their own cases. Just my 2c worth.

 

[kilohertz]

Paul Are you checking your compression with the throttle wide open? Just wondering, as this is the way you are supposed to check it. You didn't make mention of it, so I thought I would ask. I work at a tractor shop, that also used to sell Thomas skid steers. The shop foreman, who has been there for 25 years, tell me they all used 10w-30 for the hydraulics, and it is common to use this (at least in our climate). My Case 1818 uses 10w-30 for shared hydraulics and drive. The chains are also lubed with it, but separately in their own cases. Just my 2c worth.

Hi Dan, Zackary,
Well, she runs quite well now, certainly enough to put in Seafoam. I came across quite a few mentions of that as well, but thought I would start with the ATF/water as that is what I have here on the farm. I'm heading to town tomorrow and will look for Seafoam. Zackary, no, I wasn't testing it with wide open, in fact, it was right closed at idle. I'll have to check it again tomorrow when cold, then run it and check it hot again. What is the correct way to do it, hot or cold. It's been years since I was doing engine tune ups like this, on my 60's muscle cars. '68 Firebird ragtop, '68 GTO, '68 Mustang FB, '70 Mustang FB etc....;-)
As for the oil, I still haven't drained any out to see what it is. Thanks for the comments on the 10W30. It's ceratinly cheaper than Hydraulic when you go to change out 20 gallons of it. I'll decide once I do all the fluid checks.
I also need to just run this and get the fuel out of the tank and then flush it a few times to get the last of the water out. Although if I can keep it running and not clog the filter, the water may help burn out the last bit of carbon.
Thanks again all. It's nice to have the sucess this easily. looking forward to summer now so I can really use it. It's kinda hard skidding around in compact snow, although my son is having a blast playing in the 7' high pile I made in the last few days of playing with the machine.
Paul

 

[mrdeere1959]

Hi Dan, Zackary,
Well, she runs quite well now, certainly enough to put in Seafoam. I came across quite a few mentions of that as well, but thought I would start with the ATF/water as that is what I have here on the farm. I'm heading to town tomorrow and will look for Seafoam. Zackary, no, I wasn't testing it with wide open, in fact, it was right closed at idle. I'll have to check it again tomorrow when cold, then run it and check it hot again. What is the correct way to do it, hot or cold. It's been years since I was doing engine tune ups like this, on my 60's muscle cars. '68 Firebird ragtop, '68 GTO, '68 Mustang FB, '70 Mustang FB etc....;-)
As for the oil, I still haven't drained any out to see what it is. Thanks for the comments on the 10W30. It's ceratinly cheaper than Hydraulic when you go to change out 20 gallons of it. I'll decide once I do all the fluid checks.
I also need to just run this and get the fuel out of the tank and then flush it a few times to get the last of the water out. Although if I can keep it running and not clog the filter, the water may help burn out the last bit of carbon.
Thanks again all. It's nice to have the sucess this easily. looking forward to summer now so I can really use it. It's kinda hard skidding around in compact snow, although my son is having a blast playing in the 7' high pile I made in the last few days of playing with the machine.
Paul

bobcat hyd oil is less than 15 per gallon. a good 10-30 is 4 per qt

 

[kilohertz]

Hi Dan, Zackary,
Well, she runs quite well now, certainly enough to put in Seafoam. I came across quite a few mentions of that as well, but thought I would start with the ATF/water as that is what I have here on the farm. I'm heading to town tomorrow and will look for Seafoam. Zackary, no, I wasn't testing it with wide open, in fact, it was right closed at idle. I'll have to check it again tomorrow when cold, then run it and check it hot again. What is the correct way to do it, hot or cold. It's been years since I was doing engine tune ups like this, on my 60's muscle cars. '68 Firebird ragtop, '68 GTO, '68 Mustang FB, '70 Mustang FB etc....;-)
As for the oil, I still haven't drained any out to see what it is. Thanks for the comments on the 10W30. It's ceratinly cheaper than Hydraulic when you go to change out 20 gallons of it. I'll decide once I do all the fluid checks.
I also need to just run this and get the fuel out of the tank and then flush it a few times to get the last of the water out. Although if I can keep it running and not clog the filter, the water may help burn out the last bit of carbon.
Thanks again all. It's nice to have the sucess this easily. looking forward to summer now so I can really use it. It's kinda hard skidding around in compact snow, although my son is having a blast playing in the 7' high pile I made in the last few days of playing with the machine.
Paul

So I ran it around again today, got stuck in the snow for a half hour, then went for a drive down the road. Seemed to be quite good. Only started to slow down on one of the little hills. I went back up to the house and checked the compression again, and it hasn't changed, still 25 PSI at cranking and 60 PSI when running on 3 cylinders. So now I think I will be ordering an engine gasket set and pull off at least the valve covers again and make sure the tappets are adjusted correctly, and if need be, pull off the head and see whats going on. Lap the valves and set the tappets. I have run about 1 liter of ATF/MMO and about 1 cup of water through the intake in the last few days, and it is definately better, but I want all 4 cylinders to be 90 psi at cranking speed. The vacuum gauge still flutters a little at high speed, considerably more at idle. Who knows, maybe the tappets are out of adjustment and the valves aren't closing all the way.
I'll keep you posted.
Paul