751C Pug Cylinder head removal???

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t_jones98

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Dec 13, 2021
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Picked up a non-running 751C with the Peugeot in it, has some of the details of work done over the years but I doubt all. Been sitting for the last couple. One of the invoices that I received from the previous owner was for a cylinder head replacement, but no idea why. I started the cleaning process, new filters, battery, etc. Bypassed the fuel tank (haven't had a chance to flush it yet). Bled the fuel system all the way to the injectors, appears to be getting fuel, not sure about the pressure to the injectors from the seemingly problematic Lucas injector pump. Won't start. Ok, fair enough, next step, compression testing (PSIs are approx) Cyl 1 - 325-350 Cyl 2 - 325-350 Cyl 3 - 200 Cyl 4 - 75 Leads me to two conditions: 1. Cylinders, pistons and rings 2. Due to a new cylinder head, the valves were not shimmed correctly With my "test/fix/replace the least expensive first" attitude, next step is to pull the valve cover and check for valve clearance. Followed by removing the head and checking the cylinders visually, valves and seats and such. Which leads me to my main question here... can you remove the head without removing the exhaust and intake manifolds and other items that you can't really see from the back of the machine? I'm trying to do this without pulling the engine.
 
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t_jones98

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Apologies for what looks like a massive run-on sentence above, can't figure out how to keep the format when creating a post.
 
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t_jones98

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Apologies for what looks like a massive run-on sentence above, can't figure out how to keep the format when creating a post.
Ok, so further update.. could someone check my math_______
Cyl 1 - 350psi intake clearance .005, exhaust .0105-------
cyl 2 - 3125psi intake .006, exhaust .010-------
cyl 3 - 200psi intake .006, exhaust .009------
cyl 4 psi 75 intake .006, exhaust .008______
Would those close tolerances, mostly on the exhaust valves, especially for cyls 3-4 cause such a low compression?
 

flyerdan

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Ok, so further update.. could someone check my math_______
Cyl 1 - 350psi intake clearance .005, exhaust .0105-------
cyl 2 - 3125psi intake .006, exhaust .010-------
cyl 3 - 200psi intake .006, exhaust .009------
cyl 4 psi 75 intake .006, exhaust .008______
Would those close tolerances, mostly on the exhaust valves, especially for cyls 3-4 cause such a low compression?
I don't think that the valve clearances are the problem, especially on a cold engine.
Even with small numbers, they should be completely closed and not leaking, especially on a new head which one would assume had good valves when it was built/reconditioned.
If you can get an adapter to put air into the cylinder, (like the differential compression testers have) you could listen with a mechanics stethoscope for air leaking into the crankcase.
 

Tazza

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I don't think that the valve clearances are the problem, especially on a cold engine.
Even with small numbers, they should be completely closed and not leaking, especially on a new head which one would assume had good valves when it was built/reconditioned.
If you can get an adapter to put air into the cylinder, (like the differential compression testers have) you could listen with a mechanics stethoscope for air leaking into the crankcase.
Your best bet is to set the clearance to spec, then re-test the compression, then you know they should be the same, or close to it. If any are low, i'm afraid the head is coming off and possibly slapping new rings into it. If the head is already off, there is no reason changing the head gasket alone if there is a possible valve seat issue.
The idea of putting air into the cylinders one at a time at TDC through the injector or glow plug hole will help identify if it's leaking past a valve into the inlet or exhaust manifold or into the crankcase, past the rings.
 
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t_jones98

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Your best bet is to set the clearance to spec, then re-test the compression, then you know they should be the same, or close to it. If any are low, i'm afraid the head is coming off and possibly slapping new rings into it. If the head is already off, there is no reason changing the head gasket alone if there is a possible valve seat issue.
The idea of putting air into the cylinders one at a time at TDC through the injector or glow plug hole will help identify if it's leaking past a valve into the inlet or exhaust manifold or into the crankcase, past the rings.
Can the piston rings be changed with just pulling the head though? ..and not pulling the engine? Currently working to find or have my current tappet shims ground down to spec. There did not seem to be any pressure up into the head through the valve stem seals.
 

foton

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Can the piston rings be changed with just pulling the head though? ..and not pulling the engine? Currently working to find or have my current tappet shims ground down to spec. There did not seem to be any pressure up into the head through the valve stem seals.
this is a guess but I think pretty much all of these compact diesels are designed without removable cylinders, so there is no way to remove pistons from the rods unless engine is out and the oil pan off and the rods removed from crank . I have no experience with pug engines.
 

flyerdan

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this is a guess but I think pretty much all of these compact diesels are designed without removable cylinders, so there is no way to remove pistons from the rods unless engine is out and the oil pan off and the rods removed from crank . I have no experience with pug engines.
According to the online parts catalog, the Pug has a standard block, like a car engine so it has to come out to get the pistons out.
It also show no liners, and has piston and ring sets in oversizes, so it will probably have to be punched out, quite possibly to the second over judging by the low numbers in 4.
 
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t_jones98

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According to the online parts catalog, the Pug has a standard block, like a car engine so it has to come out to get the pistons out.
It also show no liners, and has piston and ring sets in oversizes, so it will probably have to be punched out, quite possibly to the second over judging by the low numbers in 4.
Thanks guys. I'm working on sourcing a couple of those valve shims. If I still can't get it running enough to just run the engine into the ground, I'm going with a Kubota conversion. I don't think the Pug is worth the $$ to put into it further. Even if just to not have to deal with a Lucas pump.
 
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