Bobcat 600 vf4d high cylinder temps

[jinx960]

Have very high cylinder temps. I'm frustrated and ready to throw in the towel. Cylinder temps after letting it idol for 20 minutes. Starts right up and runs great. Not sure what the normal operating temp is, but I would think it would be around 250??? Cylinder 1 - 410 deg Cylinder 2 - 310 deg Cylinder 3 - 450 deg Cylinder 4 - 580 deg Engine timing is good and when over 1800rpm timing is advancing like it should. Engine tins and fins are good. Good compression. No stuck valves I took of the heads and cleaned all carbon and verified valves and cylinder where moving going up/down. No obstruction in exhaust muffler or intake. New plugs and are gaped correctly. Not burning any oil. Any suggestions would be great, thanks. chris

 

[OldMachinist]

Air cooled engine cylinder heads can reach 450F at times but 300-350F is closer to normal. High temps are normally caused by restricted air flow or a sticky exhaust valve. If you're not having other problems what made you measure the temps? Also I'd double check whatever you're using to measure them with.

 

[jinx960]

Air cooled engine cylinder heads can reach 450F at times but 300-350F is closer to normal. High temps are normally caused by restricted air flow or a sticky exhaust valve. If you're not having other problems what made you measure the temps? Also I'd double check whatever you're using to measure them with.

Thanks for the reply. Temp was taken by Laser Temperature. One more thing I forget to mention. After letting it idol for 30 minutes, I checked the oil. The oil wasn't even warm. Could I have a oil pump issue???? I do have the manual but I'm far from being a mechanic. I'm a weekend mechanic at best. thanks

 

[OldMachinist]

Thanks for the reply. Temp was taken by Laser Temperature. One more thing I forget to mention. After letting it idol for 30 minutes, I checked the oil. The oil wasn't even warm. Could I have a oil pump issue???? I do have the manual but I'm far from being a mechanic. I'm a weekend mechanic at best. thanks

Sometimes a laser guided infared thermometer is not the best way to measure cylinder head temps because depending on how far away you hold it the area it measures can include the exhaust manafold. If you want to get acurate temps buy a thermocouple that mounts under the spark plug. I use one like this http://cgi.ebay.com/Washer-Thermoco...295?pt=LH_DefaultDomain_2&hash=item19c3baa077 that plugs into my multimeter.

 

[Tazza]

Sometimes a laser guided infared thermometer is not the best way to measure cylinder head temps because depending on how far away you hold it the area it measures can include the exhaust manafold. If you want to get acurate temps buy a thermocouple that mounts under the spark plug. I use one like this http://cgi.ebay.com/Washer-Thermocouple-CHT-Probe-Cylinder-Head-Temperature-/110657970295?pt=LH_DefaultDomain_2&hash=item19c3baa077 that plugs into my multimeter.

I was told many years ago by friend with a small engine shop that you should never leave an air cooled engine to idle for that exact same reason, they over heat. At idle, there isn't enough air flow to keep it cooled effectively, it doesn't make a whole lot of sense to me either, i'd figure at low speeds air flow volume per revolution would be the same if not a tad more than at higher speeds, but he has been doing this for MANY years and knows his stuff.
Give it a run at a higher speed, see what the temperatures are like. Are all the air shields in place too?
The same goes for running your ride on mower flat out then simply stopping it when you park it. The heads warp from heat. Run it hard, fine, but allow it to cool by lowering the revs, like you do for turbos.

 

[jinx960]

I was told many years ago by friend with a small engine shop that you should never leave an air cooled engine to idle for that exact same reason, they over heat. At idle, there isn't enough air flow to keep it cooled effectively, it doesn't make a whole lot of sense to me either, i'd figure at low speeds air flow volume per revolution would be the same if not a tad more than at higher speeds, but he has been doing this for MANY years and knows his stuff.
Give it a run at a higher speed, see what the temperatures are like. Are all the air shields in place too?
The same goes for running your ride on mower flat out then simply stopping it when you park it. The heads warp from heat. Run it hard, fine, but allow it to cool by lowering the revs, like you do for turbos.

Thanks I will give that a try. The air shields are on and nothing is restricting the air flow. The reason I had it at idol is I had two aluminum cylinder heads that failed because it got to hot. Actually melted the aluminum side and lost compression. I put cast iron ones on and was scared to put it under load (high rpm).

 

[Tazza]

Thanks I will give that a try. The air shields are on and nothing is restricting the air flow. The reason I had it at idol is I had two aluminum cylinder heads that failed because it got to hot. Actually melted the aluminum side and lost compression. I put cast iron ones on and was scared to put it under load (high rpm).

If they melted it sounds like its running a bit lean.... When they run lean, they burn hotter. You may want to adjust it a little, ritchen the fuel mix a little.
To melt a cylinder you are looking at over 600 degrees C, thats rather warm indeed.