Jinma 354 valve lash adjustment makes engine run much hotter

[Tim Berframe]

Hi all,

I've spent far too much time pulling wrenches lately and I'm not sure I'm getting any closer. After changing timing gear case and pump driver I decided to do the recommended head retorque and valve lash adjustment. Never done it and machine has maybe 300 hours on it (guessing as the hour clock is stuck at 18 for years now).

The head bolts were very tight except for two which were noticeably looser. The valve lash was all over the map. The intakes were 13, 9, 12, and 0 thou. The exhausts were 16, 16 18, and 0 thou. It looks like #3 never relieved all of the tension on the valve springs. I did them twice to make sure I wan't mistaken. The book says to set intake at 8-10 thou and exhaust at 10-12. I set at 10 and 12.

The engine runs a little better at high rpm. Before I would never run it at 2200rpm, that felt like serious abuse. It now actually increases in vehicle speed with throttle advance after 1900rpm.

However, the engine runs hot. It came up to 80C just idling and is just under 100C when working it for only a couple minutes. I know it is a hot summer, and the cooling system is doing its job so far but this is different than before. The hot air blowing under the cab onto my lap is not enjoyable (it might in January).

Does this sound right? It appears that the lash was larger before or I have serious wear in a short time which I don't think so. How does this adjustment affect running temp?


Not sure if it is related but I also have exhaust coming out of the engine respirator on the right side of the block. I don't recall ever seeing that before. Why is this happening?


Tim

 

[quicksandfarmer]

I'm thinking your head gasket is leaking. The exhaust is coming out of the crankcase vent, which means one or more cylinders are leaking, either through the rings or through the head gasket. Head gasket would also explain why you're running hot.

 

[Tim Berframe]

I'm thinking your head gasket is leaking. The exhaust is coming out of the crankcase vent, which means one or more cylinders are leaking, either through the rings or through the head gasket. Head gasket would also explain why you're running hot.

Not disputing what you said; just trying to understand the 'how' :

I see how bad rings or scored cylinder would allow hot gasses to blow into the base. How would a leaking head gasket allow gasses to reach the base? Pressurize the valve cover and blow down the push rod holes?


The looser head bolts were at #3 and the over tight valve lashes were at #3. I'm guessing that's the trouble spot. I would think that if the valves never released their spring tension, then the valves may not have ever fully seated and could burn. If I had a burnt exhaust valve would that allow back pressure into the head and down the push rod holes into the base? Will a compression test diagnose this without having to remove the head for inspection?

Thanks for your knowledge, you are most helpful

Tim

 

[quicksandfarmer]

Oil flows up from the crankcase under pump pressure and back down under gravity. If exhaust gas gets into the oil passages it will exit through the crankcase. The oil passages go through the cylinder head and head gasket to the engine block. If the head gasket is leaking exhaust can get into the oil passages.

I hadn't thought about a completely burnt valve. I suppose that could introduce exhaust into the oil but the valve guides would have to be completely gone -- with the valve stuck open the exhaust path is the same as with the valve normally open. Also, the gas wouldn't really be under pressure so it's hard to imagine it making its way to the crankcase.

I think a compression test is going to tell you what you already know -- you've got one or more leaking cylinders. My hypothesis is you had a cylinder that wasn't firing at all because of the valve settings. Now you've fixed the valves and it's firing and the head gasket is leaking.

The good news is that replacing the head gasket isn't that hard, I've done it. The toughest part was finding the right gasket.