compression mystery?

[Paulhenry]

Hi guys. I'm in the process of putting a second hand 125cc lifan into one of my pitty's.
The right side crankcase had a crack in it so I took one off one of my old engines (exactly the same motor ) and put it on. Only problem was that once it was on, the motor had no compression.
I took it off and the compression was back. It seems that once I tighten up the bolts, I loose compression.
I can't see anything wrong but assume that the clutch might have something to do with it?
Any ideas or suggestions would be greatly appreciated. Cheers, Paul.

 

[motodevo]

My guess would be clutch, take off the stator cover and see whether the flywheel is spinning up when kicked over or whether it is slipping. You probably need to back off the clutch adjustment on the cover and then set it once you have the cover bolted on

 

[Paulhenry]

The motor actually kicked over when I had the crankcase off. When I put it back on, I slowly tighten up the bolts and it still has compression, then as they get tighter, it looses compression. Is it possible that the crankcase is squashing the clutch, causing it to engage? My old motor wouldn't kick over with the clutch held in.

Sorry, I just got what you meant by backing off the clutch on the cover. I'll unscrew the cover tomorrow and see how I go. I don't know why I didn't think of that. I'm pretty sure that is what the problem is. Thanks heaps Motodevo. I'll post up if I can solve the problem.

 

[Paulhenry]

You were right on the money, Motodevo. I backed the clutch adjuster off inside the cover and then tightened up the bolts and had compression again. Win for me.

Refilled the oil then kicked it in the guts and she fired straight up. Another win for me.

Gave it a few decent revs and then noticed oil coming out of the top valve cover. Damb it!!!

Tried to tighten the bolts up on the valve cover ( checked every bolt, nut and cable tie I could find ) and kicked it over again. Oil leaked out of it again.

Took the cover off an old engine to compare it with my new ( also old) motor but they look identical. Swapped caps hoping that is all it will take to fix it.

Kicked it over and didn't see any leak. By this stage, it was starting to get a little late so I didn't give it a decent rev so I'll have to wait until tomorrow afternoon to test it out.

Thanks again Motodevo for taking the time to reply. It's people like you that help mechanically challenged people like me, enjoy websites like this . Cheers, Paul.

 

[motodevo]

Good to hear you got it running, hopefully you solved your oil leak too

 

[Paulhenry]

Yep. All sorted. On proper inspection, it was a damaged gasket. Now I have to sort out the muffler. I wasn't able to screw one of the studs in far enough and now it sounds like crap. Any body have any suggestions on how to solve this. I was thinking of chocking the bolt with some washers? Is there any type of heat resistant silicone that I could use. One of my other pittys exhausts had a black rubber like stuff used to seal it up a bit.