Hydraulic lock after compression test?

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MattG

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Hi folks,

Wondered if anyone has any ideas or comments on this one:

I got my secondhand 064 rebuilt a couple of months ago and it's generally been a pretty good saw. I only use it to cut the odd bit of wood up since I'm not in the tree service business. Back in the weekend I tried to start it up and it seemed pretty much impossible to pull the rope while trying to drop start. I took it back to my workshop and placed it down on the floor and tried again - but no difference.

So I took off the flywheel case and tried to turn the flywheel by hand - I could only move it slightly by a couple of degrees back and forth. I was meeting with some incredible resistance! So I removed the plug and then retried - this time I could turn the wheel and it seem nice and smooth and basically ok. Thinking "I've fixed it" I put it all back together and tried again. Still couldn't pull it round on the rope!!!

I took the plug out again, and the airfilter, and noticed a fair bit of wet around the back of the carb. Then I remembered that about a week before I'd done a compression test on the saw, in which I had I probably turned the saw over a lot, without actually starting it back up. And my mind got raceing thinking that perhaps this event was linked somehow.... After having that brainwave I tipped the saw upside down, still without the plug or filter, and pulled the saw over a bit. I believe the odd drip of fuel fell out - probably from near the carb area. Then I put the plug back in, and this time, with a lot of smoke and blubbering noise, she DID START and my smile returned. Since then the saw has been fine (I used it again the next day to check!).

I can only assume that I must have gotten too much fuel in the crankcase after the compression test, and that this resulted in a hydraulic lock in the BOTTOM of the engine somehow...

What do you guys think?

I guess I did my compression test wrong... should have unplugged the fuel line first :(
 
buzz sawyer said:
Did you have the choke closed during the test? I can't see how it could pull in enough fuel to cause a lock just from a C test. Maybe the inlet needle isn't seating well and fuel seeped past it?
Click to expand...
Hi Buzz Sawyer,

I don't think so, but I can't quite remember, I think I just had the throttle wide open. I did turn it LOADS of times, though cos I messed the test up once or twice.

(What's the right procedure for the test anyway?)

Matt
 
Actually I'm pretty sure, the choke wasn't on, cos I had the master level in OFF position. But I reckon I must have turned it over a lot cos the tester kept jumping around and getting reset. I just can't think of another explanation except hydro lock, since after starting it you could tell that it was mechanically fine.
 
lefturnfreek said:
It may need a carb kit. If the needle has gone bad, fuel is running through the carb into the crankcase causing the hydro lock and piss poor, smokey, burbly, hard start.
Click to expand...
Thanks lefturnfreek,

I did a new carb kit when I rebuilt it a few months back!

So I'm puzzled as to why it did this "lock up trick" on me. Mechanically it seems good as gold. Vac test good, starts, idles, runs real well. Just this one bit of weirdness, a week or so after I done the Comp test.
 
HarleyT said:
Check the needle, see if it holds @ 5 p.s.I..
Click to expand...
Thanks HarleyT

I'll try that later this week or in the weekend - i only changed the diaphragms and needle part when I did the rebuild, so perhaps some other part of carb is dying. (I did clean it REALLY well though).

So do you think my issue could have come from a hydro lock?

(BTW I'm at work now :-( so my replying might get patchy)
 
Don't know for sure. I don't think that your crankcase is full of fluid, as you are hinting at. As far as the flywheel not wanting to move in either direction might imply that assumption, I cannot really comment, without being there.
But it does sound like the carb is flooding.
When this happened, was the piston @ the top of the stroke, or the bottom?


On this recent rebuild, did you put in an aftermarket piston?
 
HarleyT said:
Don't know for sure. I don't think that your crankcase is full of fluid, as you are hinting at. As far as the flywheel not wanting to move in either direction might imply that assumption, I cannot really comment, without being there.
But it does sound like the carb is flooding.
When this happened, was the piston @ the top of the stroke, or the bottom?


On this recent rebuild, did you put in an aftermarket piston?
Click to expand...

I think the piston was at the bottom. However, as I said it my first message, when I first pulled the cover and the plug, I could rotate the engine by hand a couple of turns just as normal. But obviously returning the plug, w/o somehow clearing it, the lock returned.

No, it's just a regular piston, standard cyl gasket, everythings stock pretty much. When I rebuilt it I just stripped after a vac test said I was leaking at the base, fixed that with new gasket, cleaned and serviced the carb, and basically cleaned up the whole rest of it.

I wrote up my rebuild here:
http://www.arboristsite.com/community/threads/064-repair-project.288335/
 
I suppose that if crankcase wasn't full of fluid, I'm wondering if it had sufficient fluid so that each time I pulled the rope enough fuel got pushed up through the transfers into the combustion chamber to lock it up at the TOP?

I've flooded the odd engine before - but never bad enough to lock it up. I guess there's a first time for everything! ;)
 
HarleyT said:
It doesn't take much fluid to hydro-lock it.
Did you knock the carbon off the top of the piston and in the combustion chamber while it was apart?
Click to expand...

I didn't but I think it was reasonably clean (the leaking base it used to have could 've made it run lean and kept it free of excess carbon - not that thats a good thing).

I guess I can put my misadventure down to a flooding incident, if it does not happen again (in an unconnected way). Just hope that I didn't harm the seals with this accident. (Back in december they vac-tested good).

Thanks for your help/interest!

Matt
 
No, excess carbon can cause hard pulling, because it increases the compression ratio, but it wouldn't come and go. I was just asking for more info, so we can come up with ideas on what your problem is.
 
HarleyT said:
No, excess carbon can cause hard pulling, because it increases the compression ratio, but it wouldn't come and go. I was just asking for more info, so we can come up with ideas on what your problem is.
Click to expand...
Yeah cool thanks - like I say - if this doesn't happen again any time I'll put it down to user-induced flooding. I'll check it out again this/tomorrow evening.
 
Actually it wasn't so much of a "hard pull" when it had the problem - it was impossible for me to turn it over with the rope. But was I cleared whatever the issue was (post #1) it was back to normal - reasonably ok to pull for an 85 or so cc saw.
 
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.
 

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