Export thread

Hi folks I ran out of daylight and didn't get a chance to pull the valves to have a closer look. I did manage a few pics and am hoping some folks here could have a look and suggest/comment on what the picture reveals about what all may be needed. My plan was to do a leak down test but I couldn't find TDC (even though it's suppose to be marked on the flywheel) With the head off you would think it's easy to find TDC but there are 2 positions where it appears either could be TDC. Could anyone offer advice on which is which ?
Thanks

joejames said:

Hi folks I ran out of daylight and didn't get a chance to pull the valves to have a closer look. I did manage a few pics and am hoping some folks here could have a look and suggest/comment on what the picture reveals about what all may be needed. My plan was to do a leak down test but I couldn't find TDC (even though it's suppose to be marked on the flywheel) With the head off you would think it's easy to find TDC but there are 2 positions where it appears either could be TDC. Could anyone offer advice on which is which ?
Thanks

Click to expand...

Yes, I believe I can offer some advise.

The reason you are having trouble finding TDC, as you've discovered and disclosed, you don't fully understand a 4 stroke engine.

As the piston advances toward the head on one of its travels ( turning the flywheel the direction of operation ) the exhaust valve will be open and that valve will close as the piston reaches TDC on that stroke. That just completed the exhaust stroke of the 4 strokes.

The next time the piston advances toward the head both exhaust and intake valves will be closed the full duration of the piston movement toward the head. This time the compression stroke has just been completed and you just found TDC on the compression stroke. The one you are looking for.

With the head off and both valves closed you can check for valve leaks by putting about a half teaspoon of water around them.

Thanks! So basically you're saying once you see the intake go from opened to shut as the piston comes flush to the top, then that is TDC. Easy enough! Thanks for your help. Another question I have is dealing with cleaning up the carbon on both the head and the piston/top of jug. What is the best/easiest method to remove all that carbon?

joejames said:

Thanks! So basically you're saying once you see the intake go from opened to shut as the piston comes flush to the top, then that is TDC. Easy enough! Thanks for your help. Another question I have is dealing with cleaning up the carbon on both the head and the piston/top of jug. What is the best/easiest method to remove all that carbon?

Click to expand...

No, I did not say that.

Your quote: "once you see the intake go from opened to shut"

When this happens the piston will be near the bottom of its stroke after just completing its suction stroke. As the intake closes the piston will then advance toward the head on its compression stroke. At the top of this compression stroke is the TDC you are looking for.

I understood what you meant, I just did a poor job of interpreting in words. I said, "once you see the intake go from opened to shut **as the piston comes flush to the top , then that is TDC

joejames said:

I understood what you meant, I just did a poor job of interpreting in words. I said, "once you see the intake go from opened to shut **as the piston comes flush to the top , then that is TDC

Click to expand...

Yes, that's correct. The piston just completed the compression stroke when it got flush at the top.

Joe, Since you have the head off put a prick punch mark at tdc. This can be very precise, but probably not needed on a 3000 rpm unit with no ignition advance curve. At tdc there is a dwell period where the piston does not move as the crank turns. The pros probably will tell you "hey its a tractor motor, so find tdc with a screw driver or something and get on with it." My Intek tdc is right where the f wheel magnet meets the leading edge of the coil, but don't rely on it. And the fan shroud must be removed to see that setting - time consuming. Also the base circle of the cam is very "long" in degrees, which does not require perfect tdc for valve adjustment. I suggest spending the time on other things like assuring the engine is not eating dirt.

Why are wanting to do a "leakdown" test? What is your problem? Just take a good wire brush and clean off that carbon, check your valve adjustment and put in a new set of points and condenser and you should be good to go. Maybe do a correct valve job while you have it down this far, with it torn down, a competent shop shouldn't charge too much to correctly cut your valves and seats.