what would causes this?
i think i heard something about the Gila piston not being made for a right turning crank. ????ANyone
hard riding over a long time
poor quality wristpin bearing and or worn wristpin bearing
poor quality wristpin steel
slightly mismatches part tolerances
or a combo of all of the above.
i think its bad/worn parts man. For example i have noticed that some cranks come with higher quality (feeling and looking only not other way for me to tell) needle bearings than others. Its been my experience that needle bearings (not necessarily on cranks) tend to fail faster than most other types bearings.
dude u ride is fast and breaks shit like all the other fast bikes lol
Ya the piston pin offset is made for the other roatation but thats not his problem. To get that pin out of the piston you must have scratched the pin boss in the piston some. It's curious to say the least. It appears your roller brgs are intact. It may be inferior metal in the pin otherwise the rollers would be fucked also. Even if the piston bosses have scratches in them I would try a different pin and new roller brg and see what happens. Your piston is staying cool. No carbon on the underside. If detonation was banging the bearing surfaces I would expect the piston to suffer first. Anyone have a answer to this?
i fucked the piston up getting it out, the pin on a previous stock crank busted the the bushing loose and the pin was seizing inside this piston i slightly sanded the pin down and fit smothly inside bearings/piston.
the needle bearings are still intact and turn fairly easy but do feel wonky white turning it in the crank with a pin.
Yeah, all part of the fast bikes tearing shit apart club.
Probably just has to do with the parts we are using not being meant to be put through the kind of abuse we put it through.
That or the builder just didnt know what he was doing ;)
80 kits going 30 is how i roll
Yeah the big end of my con rod did the same thing , 7occ power and 50cc parts make for a short life . Well and its pretty old too .
problem: insufficient lubrication
Solution: drill extra oiling holes in the small end of the connecting rod, similar to a brass bushing oiling hole.
may be difficult to drill with a simple cordless as the metal is super hardened. make one on the exhaust side and one up top. less than an 1/8 inch.
i also drill holes where the wristpin enters piston. see stock puch piston for example.
gila piston has oiling holes.
look at pick above. it does not. i'm talkin about where the wristpin goes. check out old 49cc stocker and you'll see buddy.
Race cranks don't have the holes either, again, see stock counterpart.
Whoa, my gila piston totally has holes. I have two gila pistons and they both have oiling holes. I dont know why his doesnt.
The dmp stuffed crank has an oiling hole too. Its the only crank I know of that does.
poo poo head
wierd. no holes for him. wonder what crank he had?? is the hole on the exhaust side?
Yeah, I believe its on the exhaust side. Wonder if he used a metra piston? I've had two gila pistons and they both had the holes.
sometimes they have holes sometimes they don't, i have drilled them before guess i really need them and small end has no holes damn it!
Put a stuffed DMP in there. It has the small end holes. Cranks and damn hard to drill through and put your own hole. I know people are skeptical about the DMP stuffed, but its a damn good crank minus the slight possibility of the stuffing coming out. Hell just pop the stuff out before hand if you dont mind having a non-stuffed crank.
Thats weird that your piston didnt have the oiling holes, the one that came with the kit, and the one I bought separately both had them. Didnt know they had ones without it.
the wrist pin shouldn't be rotating in the piston at all. that galling looks like it came from too tight of a tolerance, you 'sanded the pin down'? they also usually have a precision ground finish from the factory.. when i have to re-size pins i put them in a lathe and use 400,600, then 1200 grit emory cloth to put a good finish back on them. i would guess the pin heated up and bound in the bearing.
So i popped my top end (airsal) off tonight to see why i lost like 10mph on the way back around the lake from seattle monday night, and this is what I found
whats wrong with this picture?
The pin had melted/worn one side of it's seat way out of round and off center. I can't believe i made it home. Thankfully i have a spare piston. I was reading this thread the last couple days, so I just drilled these, hopefully they will help.
I managed to come through pretty clean on the other side, and an old wrist pin slid right through, but i'm worried they might scratch the new one, any tips on cleaning up the pin bore other than some fine emery cloth?
I still have to address what I think may be the root of the problem, and that is the brass con rod bushing is worn a bit out of round, i can wiggle the wrist pin in it a little, i figured the tolerance was pretty loose to allow for thermal expansion, but how much play is too much?
And for the viewing pleasure of folks who have not seen them here are the double all the way through the side of the bore oil holes on the stock piston, i wish i had the tools to replicate these:
(#22 2hp high torque, dykes 'L' ring flush with crown)
good bushing to pin clearance is real small. .0005 inch or less. You need a micrometer and a suitable reamer and a new bushing. The new bushings specifically sold for this application may be able to be installed with little or no reaming involved, I don't know
good pix. thanks.
New bushing time for sure. Make sure that you also put a hole in the new bushing once you get it pressed into the crank.
thanks guys. was up a bit late last night, just went through the manual and it does have the details (<3 the puch manual, compare to vespa! lol). have to go to my folks to grab the good good micrometer, hopefully 1977 still has some bushings left.
Oh yea if you need to measure the ID of the bush you can use a snap gauge
so I got a new bushing in today (along with some other little stuff, thanks 1977 for the quick shipping! and stickers too, running out of room on my toolbox lol). anyway, it also has noticeable play on a brand new wrist pin, and not much less than my old bush. the old bushing does have obvious heat/wear marks so I do plan on changing it, but going to try my stock jug which i got bored, cleaned up, honed, and matched to my case over these last few days.
I also have an idea for a home made bushing extractor tool made from a couple of appropriately sized pieces of pipe, a bolt, and some washers. I will do a little wiki write up if it goes well.
p.s. commando sorry to hijack your thread, got an update for us?
gila pistons have oiling holes, the metra pistons that gilardoni co-opted do not.
to clarify: original gila pistons have the holes, ant then after they switched to metra pistons they didnt have holes. If you bought a gila kit in late summer/fall, they would be metra pistons.
Why would you need oiling holes there? The pin doesn't move. That what the bearing is for, right? I don't get it.
because bret, you just cant pump it over and over again into the same hole without lubrication. It gets hot and friction burns result.
i know what you guys that are saying the pin does not move in the piston are coming from, once everything warms and expands the piston holds it tight, but why the oiling holes then? i think these might not work like that, i know automotive pins are way harder to drive in, have to heat the piston in an oil bath to over 100 degrees F for the pin to slide around in both my VW and Mitsu engines..
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