top end overhaul 81 marathon - is it worth it

[jmaxwell47]

well I fixed the no running issue, as easy as taking the fuel filter out between the pump and carb as it must have been clogging so now its running "fine"

My question now is when do you know its time to replace/overhaul the top end.

the full kits are relatively cheap and looks easy enough but my question is how do I know I need to overhaul. Do I need to get something to test my compression to know for sure, if its sluggish running and uphill prob only gets to 8 mph, assuming that's a pretty good indicator??

Open to hear any opinions and watch outs if I decide to redo the top end.

[jmaxwell47]

can't find the delete post button

[Dabble Inn]

Need more info, are you premixing? Is the Gov still hooked up? Use an NGK BP5HS spark plug gapped at .028-.030....

Yes a compression test is a great idea, get one and let us know what you have and we'll go from there.

I will say, even if compression is low doing just a top end may not fix the problem. The correct thing to do is also split the case and replace the crank bearings and seals, especially the seals. Worn seals will make it run very poorly.

[cart around]

It could be a belt or clutch issue too.

[jmaxwell47]

Originally Posted by Dabble Inn

Need more info, are you premixing? Is the Gov still hooked up? Use an NGK BP5HS spark plug gapped at .028-.030....

Yes a compression test is a great idea, get one and let us know what you have and we'll go from there.

I will say, even if compression is low doing just a top end may not fix the problem. The correct thing to do is also split the case and replace the crank bearings and seals, especially the seals. Worn seals will make it run very poorly.

1 - premixed gas at 1oz per gal (the oil tank was deleted already when I got it

2- dont think governor is "on" if that's the cable that runs beneath the throttle around and over to the drive clutch

3 - spark plug in it now came in a tune up kit so prob not an NGK but ill snag one when I grab the compression tester from oreillys

4 - there's a decent clunk when in Forward/Reverse in the time it takes a minute to engage after putting foot on the pedal...while im at it what should I be looking at to "fix" that

I'll get a new spark plug in it and test compression while swapping and see how that works. thanks for feedback

[Dabble Inn]

Correct on the mixture, sounds like the Gov is indeed unhooked if you mean the cable that goes to the 'driven' clutch.

If I'm thinking of the same slight clunk noise when changing direction it's a normal noise....

Keep in mind what 'Cart Around' above suggested too

[jmaxwell47]

Compression test - not sure if I’m doing it right but unhook fuel line and screw in tester into spark plug hole; when I step on pedal to turn it over, if I let it turn over 2 times it’s reading 60 and when I hold the gas pedal down to turn over 5-6 times, the highest it gets is about 80-85.

Gonna put the new plug in and see if it helps any but guessing that compression is a little low and may be worth a top end rebuild…

Not sure I have a comfort level to split the case and redo the seals but looks like I’ll be YouTubing a few hours to see what I think I’m capable of.

Any thoughts suggestions??

[cart around]

Hold the pedal all the way down and let it spin. It's only going to go as high as it will. You can't over test.

120 is new. 100 is perfectly acceptable. 80 is getting low. I don't think it will run less than 60.

You only split the case to replace the crankshaft bearings. To replace the seals, you remove the clutch and flywheel.

You never said anything about measuring how wide the belt is, or if you can squeeze the plates together with one hand on the driven clutch. It should be very stiff. You should not be able to make the plates lean towards each other by squeezing.

A new belt is 1 3/16" wide. Anything less than an inch is junk.

After reading your original post again, I have two questions.
How big is the hill?
How much do you weigh?