Piston slop - lmao

killercanuck

killercanuck

New Member
Okay, a little preface before I get into this. On one of my bikes for the past couple of weeks I've been fighting some grinding on my clutch cover. The slop in my large gear was causing the gear to 'grind' on the cover at high rpm. I could clearly see where it was hitting the cover. So instead of replacing the whole clutch unit(and those 57-3mm bearings), I got out the Dremel and had at it. Just to give the gear more clearance, I added a couple more gaskets for good measure.

But I was still hearing the grinding sound.... So I double checked my cover, which I permanent marker'd the inside(after dremel) so I could see if it was still hitting, but there wasn't a scratch.

Uh Oh...


Plus I was starting to lose power...



Double Uh Oh!!



So I decided to pull my head off and have a look:

Aww Crap! What are those dings in the head from!!??


So off the jug came......

Good lord almighty! There was a 'little' play in the wrist pin, and I say little like mount Everest is a molehill:

It spun from here:
piston-pos1.jpg


To Here!!:
piston-pos2.jpg



That ain't right, is an understatement.

So I got the wrist pin out with a little persuasion and...

The bushing was completely gone! And it still ran! Not well, but it got me home...
bushing-lol.jpg



And all that play caused the piston to chew on the transfer ports:
T-portchewed.jpg


And both sides of the piston:
Piston-chewed.jpg




I'm baffled that it still ran.





So anyways, I know I'll at least need to replace the top-end. But how much lateral play should there be in the connecting rod? I've got about a 1/4" side to side at the top. Should I just junk this engine? Or is it salvageable if I can get the bushing chunks out of the bottom end?
 
You should have a few hundredth of an inch of side to side play in the connecting rod. A QUARTER INCH!?!

Just goes to show you that there is no such thing as "precision engineering", since it ran that way. Who needs close tolerances? ;)
 
Few hundredth, D'oh! Well I just measured and its only 3/16" play, but still... it friggin ran like that, boggles the mind.

Anyone have an extra engine kicking around? I'll pay for shipping and a couple boxes of beer for ya :p
 
where are the snap rings from the ends holes of the wrist pin hole(?)
and the parts of the missing bearing?
are the in the main case and main bearings?
 
I pulled the G-clips, all that was left is what you see in pic #3. I set the pin back in to show the amount of play it had. The bushing was completely disintegrated. Pics 1 & 2 show the amount of play. I'm still baffled it actually ran and got me home tonight.

It just goes to show the resiliency of these little motors.
 
Holy missing bearing! I'm amazed that the thing was turning at least 3k rpm with that! How long have you had that engine? If your bottom end is not torn up, replace the top end and put a quality needle bearing in the small end of the con rod and go!
 
1k if I was lucky, the 'grinding' was horrendous! lol I didn't push her because I wanted to get home without pedalling.

I would've went for just a top end, but there's 3/16" play at the top of the connecting rod. So it's only a matter of time before the bottom bearing goes too.

I got the engine/bike used off of Kijijji for cheap. Now I know why... when I got it- the bottom of the intake gasket was gone, and the plug was pure white. Who know's how long they ran it like that for... But I figure that's why the bushing ended up in the bottom end, lol.

Luckily scotto- hooked me up with a clunker of his, mounting bolts chewed and whatnot. but the internals are good, so I should be able to scavenge the top end and the crank to throw in this case. It should be on its way anyday :)
 
1k if I was lucky, the 'grinding' was horrendous! lol I didn't push her because I wanted to get home without pedalling.

Thats rediculous!!!!

I guess the engine was starved of oil and the guy sold it cuz it was running like crap, figures. Pull out the mounting hardware from the new engine with two nuts and replace it with 10.9., unless you are really attached to your old case. Glad to hear you got another engine so quick, finding one is easier than finding Schwinn S-7 tires and thats whats holding me up right now.
 
It ran great for a few weeks, then it ran better for a few days before it crapped out. Like my dad always told me "Engines always run better just before they die", so I'm inclined to believe the sentiment, even though the outcome sucks!

Oh yea, the last owner wasn't even aware that the bottom of the intake gasket was missing. So it was running 'mad' lean (ie. plug was white as paper :( ). I replaced the gasket after I got it and gave it a 'once over', but the damage was already done.

I don't really trust the bearings on the end of the crank either, they could crap out 20k after I change the top-end...

so...

The replacement case that's coming has had extensive work done on the rear mounting studs, so I could try it, but in the end I think that's unreliable compared to a decent case. Plus I've never cracked a case open before, so I'm looking forward to swapping the crank(and bearings) actually.

I wish I had the money for one of FourEasy's balanced cranks while I had the case open! But that's just not feasible at the moment.

Thanks for the interest and suggestions guys! :)
 
Hey juliman, Foureasy makes and sells balanced cranks(with real bearings) for around $100, drop him a line via pm for more info.
 
killercanuck said:
Few hundredth, D'oh! Well I just measured and its only 3/16" play, but still... it friggin ran like that, boggles the mind.

Anyone have an extra engine kicking around? I'll pay for shipping and a couple boxes of beer for ya :p
Click to expand...

The " sideplay"in the lower rod bearing isn't checked by how much the top of the rod wiggled. Even a new one will wiggle a lot that way.

The sideplay is checked bt using feeler guages between the rod journal and the flywheel.
the running clearance of the bearing is measured by using a dial caliper or dial indicator and push and pull the rod for a reading
 
Hmm, sounds like my experience with my last engine. I kept hearing a squeaking noise at low speeds. I figured it was clutch dust and junk in the case, or maybe bearings. It started running fine again, though. I thought maybe the gas had just been a bad mix. The next batch was carefully measured. I wound it up to 35 and it was running hard like before the squealing. Then BAM. i had to check my nuts. Still there.... But the top end was locked up. Shattered piston, rings broken in multiple pieces and shot into the cylinder ports and walls, top piston connection wasted. Strangely enough though, the bottom parts seemed fine. The connecting rod can be moved by hand and the bearings seem ok with no extra play or noise. I just boxed it for spare parts though. Not worth $50 worth of stuff for the cylinder head and parts, when it might crap out again.

re: It ran great for a few weeks, then it ran better for a few days before it crapped out. Like my dad always told me "Engines always run better just before they die", so I'm inclined to believe the sentiment, even though the outcome sucks!
 
I think it self-destructed from lack of back-pressure. A friend of mine who is into dirtbikes and motorcycles said the drilled out muffler I had used killed it.

I didn't port it. I only took the top off after engine break in (no trouble then) to loctite the studs and check for scuffing. Everything looked good, so I reassembled it with a light grease and ran it for months with no trouble. I think the combo of the low gear (44t wheel) and WOT runs all the time, with the crappy gas here, and the open muffler, did waste one of the rings, and when it stuck in the port, that was all she wrote. That would explain the intermittent squealing, and the sudden lock-up.
 
I think that engine was pretty wet. I used 2cycle oil in it at about 32:1 after break in. It never had burned plugs. I just chalked it up to a broken ring, and got another engine for $80.

Oh well, the next muffler I used (on new engine) has much more pressure. The engine runs well, and the 36t sprocket seems to do better. I run 8oz oil: 1 gallon fuel. Hope this one lasts longer!
 
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