Feeling your pain
 

Your last post got me thinking, you may want to make sure you re not missing any air cleaner or butterfly plate screws, Just a thought to go with the statement of finding something in the combustion chamber.

I understand the statement of bugging you every minute. These little beast seem to do that to you when somethings not right with them.

Can't give away all the secrets before the bets are made! :biggrin2::biggrin2:


You are right about timing though Frank. It is possible.

I'm sticking with valve issue.
(Just so it's clear, that's a non-specific claim..... ANY issue found with valves is my bet. Not just "out of adjustment"...)

Not knowing just asking.
Does that engine have an "Automatic Compression Release"?

Yes. :beerchug:

I think since the stakes on this bet are so high I'm going to ask for more than just valves.:biggrin2:
Since it was just rebuilt I'm going with not enough stem to guide clearance, maybe the reamer they use had reamed too many guides and was worn.
It's just a guess though. And I'm usually wrong!

You play it safe...:biggrin2:

This included the valves, valves seat, valves guide, valves spring and even the small levers on the camshaft that trip open the exhaust valve at low turning speeds to reduce compression.

Smart bet:beerchug:

:biggrin2::biggrin2::biggrin2::beerchug:



So far I'm the only one who says valves, so we'll see if I'm right.

Yup. Valves it is. :BB&YS:

Had a little time to poke around the cub this evening. My feeler gauges went AWOL, (I have 3 boys and share property with grandpa, common problem), but I don't need them to see what's going on.
Basically, the exhaust valve is slightly opening during the compression stroke!
Watching the valves and the piston (through the peep hole) with breather removed, turning engine clockwise (from drivers seat):
1. Intake valve opens as piston moves downward (aka intake stroke)
2. Piston moves upward (aka compression stroke) but about halfway through the stroke, the tappet presses on the exhaust valve, slightly opening it (observed at tappet and through spark plug hole)
3. Power stroke seems normal
4. Exhaust stroke seems normal

I'm not an engine expert, but I'm pretty sure it's not supposed to work like that. As stated, the engine acts like there's no compression, now I can see that is exactly the case.
I took video, but no idea where to put it or how to post it.

So, what's next?
1. Is it common (or not so common) to have a cam (Lifter? Roller? I have not got that far in studying these engines...) slightly out of round, and a proper valve adjustment will compensate for the difference?

2. Should I stop messing with it, stop turning the engine, learn how to tear down and rebuild and then do it before I screw something up?

Still irked about the whole situation. It would be one thing if I bought the cub from Joe Shmoe with a yard sale sign, but this came from an IH Dealer/Family, I drove it out of a barn full of cubs (talked with the owner about making a future offer on a broke down 108 shoved in a back corner), one of the guys ran back to the dealer shop to grab the 4" binder full of every manual I could want, I spoke with the guy who had just rebuilt the engine, claimed he'd done it for the shop all his life. I never imagined I was driving 2 1/2 hours and paying good money for a cub that would blow up 10 min after I got home...

In other news, blew a pretty bad oil leak in the 680 while mowing today. It was too hot to mess with so I haven't even pulled the engine shrouds off to see where it's coming from.
Apparently, my comment about 5 K series engines and never having to do any internal engine work is coming back to haunt me...

Why does that feel like deja-vu?:biggrin2:

http://www.onlycubcadets.net/forum/s...ad.php?t=36455

Read posts 5 and 6.