QuestionQUESTION: Hi
The system wouldn't let me ask another question last time. The model number is 71-52118-1 Serial number is 101991-1296 Craftsman 8hp 25in wide snowblower. I have taken the cylinder head off and have piston at top dead center both valves are open. Intake valve is carboned up and exhaust is white in colour. What is the next step? Thanks
ANSWER: You can remove the valves and clean them but you really should lap or cut the seats to make sure they are sealing. I used to just lap before I had a cutter...lapping works just fine but it takes more time. Once lapped or cut, you will have to re-gap the valves.
There are several You Tube videos on lapping valves.
https://www.youtube.com/watch?v=6BX5ab12-Wk
If the URL does not work just search You Tube for "valve job on tecumseh engine part 4".
What is the clearance on each valve?
Eric
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valves
top dead center piston
QUESTION: Hi
I have attached pictures.I can't get the feeler gauge in between the valve stem. The first picture shows piston at top dead center and both valves open and I can turn them with my fingers
ANSWER: Is the piston at TDC on the compression stroke? Just turn the engine by hand, follow the strokes, intake (piston goes down, intake valve opens, compression (piston comes up intake closes), power stroke (both valves closed, piston goes down), exhaust (exhaust valve opens piston comes up).
Turn the engine for a couple of cycles following the strokes. After a couple, stop at TDC on the compression stroke and check the clearance.
BTW, what you are feeling is valve overlap. Overlap is normal on all 4 cycle engines at one of the TDCs...if there is no overlap on one of the TDCs then the mechanical timing is off and the engine will never run.
I believe you are on the overlap TDC which is why you can not get the feeler gauge in to measure the clearance. You should be able to rotate to the next TDC (compression) and both valves should be closed. One valve may be open slightly, use your fingers to check, as this could be the compression release which keeps one valve slightly open so you can pull the starter to start the engine. Once running the cam is spinning so fast the compression release has little impact on the power or efficiency.
Eric
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top dead center piston
QUESTION: ok.....That makes sense I will cycle it through I downloaded two of the same pictures by mistake here is the original top dead center picture with valves up
AnswerI have not noticed that much valve overlap but I usually do not visually look at the overlap...I just feel with my fingers to see if I can rotate the valves then I know overlap is there.
I'd cycle to the next TDC and see if you have any clearance. Also, you might try using a small screwdriver and making sure the valve tappets are full resting on the can...just make sure nothing is holding the tappets up which is causing the valve to be open.
Eric
