Hydraulic lock after compression test?

[MattG]

I rebuilt an 064 @ 8 years ago for a customer. He brought me a Golf piston to use. After I put it back together, It would
stop at the bottom of the stroke. I compared the piston closely with the old one, and the difference was that the inner lip
of the bottom of the piston had a bevel on the oem, and the aftermarket one didn't, and the piston bottom was hitting the
counterweight. Which is why I was curious as to the saw's history.
If this was my saw, I would pull the cylinder and have a look around in the crankcase to be safe.

Yeah, interesting. I'll bear that in mind. When I next strip it.

Bad news, got back from job. Took off flywheel cover - no obstruction. Stripped off clutch, worm drive etc. - no obstruction. I didn't test the carb - have a busy night. Anyway I threw it back together and the thing was locked up again!!! I loosened the plug and turned it by hand, then reassembled AGAIN, and it's ok again. I then test started it and it was ok.

I hate intermittent faults!! I did think "well perhaps you're too much of a wimp" to have one of these saws. But when it's ok, I find it pretty easy to turn over. In fact I can usually quite easily either turn the crank a couple of rotattions by hand on the flywheel, with the plug in, or by the rope. It's just that on these odd of occasions this weird thing is happening.

The only other thing I've done lately is changed the clutch (the carrier and drum). I used stihl parts and I cant see anything obvious wrong with how I fitted them.

Harley - I'm guessing that thing you mentioned with the piston would happen all the time - not interrmittently?

 

[MattG]

I just don't get how sometimes it's real easy just too pull the rope round by hand and other times I'm pulling somemuch I'm thinking that somethings going to break soon, like the rope elastic is about to snap, or the AV joint about to rip open. Then I'm thinking "yup there's really something wrong here...".

 

[lefturnfreek]

So it locks up and it won't turn in either direction.....What I don't get is you can pull the plug and it turns over.... is the plug hitting the piston?

What happens if drain all the fuel and the carb out, and leave it sit?

 

[MattG]

So adding cause and effect to my fault diagnosis - it seems the saw was fine - never showed this issue to me, until about a week or so ago, when it did this comp test and replaced the entire clutch assembly. And like I said, once I've freed it off - it starts and runs just fine.

 

[lefturnfreek]

Hmmmm......

Get it running and drain all the fuel in the tank and run out the carb and see what happens....

 

[MattG]

So it locks up and it won't turn in either direction.....What I don't get is you can pull the plug and it turns over.... is the plug hitting the piston?

What happens if drain all the fuel and the carb out, and leave it sit?

Hi leftturnfreek,.

No I don't get it either. Clueless. I might try your idea sometime soonish though. Just wish I had more time for this
I've the usual array of domestic and car maintenance on my plate aswell right now. Just wish there was a simple answer! If anyone else has any more ideas pls let me know. I'll post back if i get a chance to conclusively figure it out.

later
Matt

 

[MattG]

Hmmmm......

Get it running and drain all the fuel in the tank and run out the carb and see what happens....

yeah cheers man... I'll try these ideas soon and post back.. I gotta dash now.. swimming night for me and my eldest kid right now. Light relief from chainsaw maintenance

 

[HarleyT]

Pull that cylinder off, make sure you don't have some bearings coming apart!

 

[MattG]

Pull that cylinder off, make sure you don't have some bearings coming apart!

Did wonder about bearings tightening. Damn weird whatever. Reckon a big strip down is a couple of months away what with my dosmestic workload

 

[lone wolf]

So adding cause and effect to my fault diagnosis - it seems the saw was fine - never showed this issue to me, until about a week or so ago, when it did this comp test and replaced the entire clutch assembly. And like I said, once I've freed it off - it starts and runs just fine.

Well take the clutch off and try again.

 

[wcorey]

At this point I'd say HarleyT is right, take the jug off and check for bearing issues, failing cages could cause this issue.
I bought a seized ms260 on the cheap and the problem was the plastic cage had separated and was jammed up between the case and crank. No other damage but if it had been a metal cage...

 

[CR888]

I am with the Wolf, I'd take the clutch off and go from there. It could be a heap of potential things but as you replaced the clutch, then the problem raised its head.

 

[marti384]

Make sure there isn't a lot of fine sawdust in the intake tract. I had a high compression saw that became impossible to pull over when the air filter got a small hole in it and it sucked in a lot of dust. Really boogered up the bearings, they became packed with dust. I could turn it over with the plug out, but with the plug in, the combination of high compression and bearings packed full of oily dust made it impossible.

 

[MattG]

Well take the clutch off and try again.

Yeah, that's what I'm thinking. Did wonder if I put the drum on wedged a off centre, or that the big washer+e-clip was too tight against the drum. Something to do pretty easy. Just be nice to be able to repro the exact fault first!

At this point I'd say HarleyT is right, take the jug off and check for bearing issues, failing cages could cause this issue.
I bought a seized ms260 on the cheap and the problem was the plastic cage had separated and was jammed up between the case and crank. No other damage but if it had been a metal cage...

Hmm.. Which bearings I'm looking at for most likely issues? Do you mean the little end bearing at top of the rod, or the big end bearing at the bottom, or the two main bearings on the crankshaft ends? Can you actually see the main bearings well with just the jug off?
So if this theory is correct if the engine is stopped at a rough spot would it be locked up solid, but if on a smooth spot free to turn round ok. Does sound plausible.

Make sure there isn't a lot of fine sawdust in the intake tract. I had a high compression saw that became impossible to pull over when the air filter got a small hole in it and it sucked in a lot of dust. Really boogered up the bearings, they became packed with dust. I could turn it over with the plug out, but with the plug in, the combination of high compression and bearings packed full of oily dust made it impossible.

Thing is with this, is that the lockup is only intermittent, once I've freed it (so far by pulling plug and moving by hand) then it seems just fine. And can pull over plenty. I guess your issue made it hard going pretty much all the time?

Well, if it's needing major work, I'll have to rebuild again in a few months. I've too much other stuff in my life right now for this! I mainly posted this thread to see if there was an easier answer.

If the worse comes to the worse and it's a main bearing problem - can I find any threads / advice on AS for how to do bearings properly? Can I PM any of you guys for help on this subject at a later date?

thanks again for help
Matt

 

[blsnelling]

Check for radial play in your crank bearings. If the cage is gone, the balls will bunch up on one side intermittently.

 

[MattG]

Check for radial play in your crank bearings. If the cage is gone, the balls will bunch up on one side intermittently.

Thanks Brad,

Do you mean just grab the flywheel and crankshaft on the clutch and see if I can wobble it about much? Pretty sure I did all that a couple of months ago when I vac tested - and it seemed good. The saws scarcely done 2-3 hours of work since, so I imagine it's still good.

I'm gonna mess about with it this evening just to if reassembling the clutch side/drum/washer etc. re-exposes the problem - so I'll have another check for up-and-down at the crank ends then.

 

[blsnelling]

Yes.

 

[MattG]

Ok,

This is all very embarrassing.

99% sure that I have figured it out. If there is ever an award for idiot mechanical mistake then it has to go to me. There are 3 screws to hold on the shroud. See below:

[photo=large]3739[/photo]

One of the screws is larger than the other 2. I guess you are supposed to use this screw on the PTO side. You should NEVER EVER use this screw at the fixing point on the flywheel side, toward the front. If you do you find that because it's longer it goes all the way through to the flywheel and typically jams in between 2 flywheel vanes acting as a very nice CRANKSHAFT stop. After lots of taking off new clutch / putting on old clutch / replacing the shroud etc. I noticed a weird tingy noise (the screw thread scraping against the flywheel vane!) then I thought "that's odd" and checked the crank and it was locked. Then I took off the shroud and it was unlocked.

The reason why I got a couple of degrees movement when locked should be clear now! And the reason why I thought that pulling the plug (and hence the hydro lock theory) was the deal was because I usually find it easier to get the plug out this way!

I suppose that the lesson is whenever you have screws of varying lengths - question why! Anyway sorry to waste everyone's time - but hopefully the story does have some amusement value.



Thanks again for your patience and help, as usual...

 

[blsnelling]

Been there, done that

 

[MattG]

Been there, done that

Just glad it wasn't anything more serious, like the bearings!