gt 80 piston small end wrist pin bearing and big end

[sp1ke]

main bearings feel loose like the bearings are a size too small or something on both of them there was some grit like a bit of sand i had to clean out and the bearings skipped over it easyly they got cleaned and greased better ones would be ideal

i also noticed that on one side the bearings seated with almost no pressure so definatly a cheap knock off but ill make it good

the up n down movement was very noticeable on the small piston bearing

 

[Street Ryderz]

No I'm sorry but that's not correct, there are definitely 2 different sized bearings used in these motors, question is how often... I will dig through the paperweight box and see if I can get this out there.

I have built,worked on every variation of these engines literally 100's of them over the last 16 years and have never seen a different size other than length,This is what I do for a living and trust me I am always looking for ways to improve these !

 

[Street Ryderz]

main bearings feel loose like the bearings are a size too small or something on both of them there was some grit like a bit of sand i had to clean out and the bearings skipped over it easyly they got cleaned and greased better ones would be ideal

i also noticed that on one side the bearings seated with almost no pressure so definatly a cheap knock off but ill make it good

Yes I would replace them!

 

[sp1ke]

lol thought so so next question is what exactly am i looking for do u know the dimensions ? and what were the other bits about clearance and ball size rateing ? i saw them somewhere here i think




http://motoredbikes.com/threads/how...cc-66cc-last-forever.33746/page-3#post-423205


Change main bearings for to skf 6202


someone said

changing the crank bearings over willy nilly can sometimes do more harm than good.

theres a little extra numeral on the end, called "clearance"... you want c3 or c4 bearings for crankshafts, they start a little loose, so they get tighter as things start heating up, etc. (this is not the ABEC number, that is simply how ROUND bearings are. 3 being lousy cheap nasty ones, 11 being really expensive...)

run c2 and they WILL seize. run cn, the standard bearing off the shelf, theres a possibility they will seize.

all reputable manufacturers run c4 bearings on cranks. one of the reasons OEM bearings are expensive, besides dealership markups, is that they are produced in small lots for specific purposes. C4 is not a common tolerance...

also an idea to run sealed bearings and pop the inside seal off, 2nd line of defense considering how pathetic the crank seals are in the HT engines...

im not saying not to change the bearings, but to be careful if you DO.

this in mind am i forgetting anything other then dimensions

 

[Street Ryderz]

most likely a 6202 c4 or 6203 if a 17mm crank you will have to measure to make sure!I just take one with me to the supplier and tell them its for a crank then they will show you the spec's

 

[Steve Best]

Crank bearing sizes:
Older motors were 6202-C3, they are 15mm x 35mm x 11mm
Newer motors are 6203-C3, they are 17mm x 40mm x 12mm
C3 is the clearance on the balls.

The clutch/sprocket shaft on all take 6202-2RS sealed bearings.
2RS stands for 2 Rubber Seals.
Shielded bearings come in most of the clutch shafts, but I would recommend the sealed bearings.

All these bearings cost between $5 and $15 depending on manufacturer and where you buy.
Be careful that there are some specialty 6203-xx bearings that have oddball characteristics.
I was sold some at my local small-gas/lawntractor place that had 5/8" bores.

 

[sp1ke]

so if 17 mm 6203 otherwise 6202 15mm

Z (metal ) C3 SEALED BALL BEARINGS
from what i can see avg size would be
17mm ID x 40mm OD by 12 wide

 

[sp1ke]

thanks for all the great help everyone i know far better what im doing now

 

[Street Ryderz]

Crank bearing sizes:
Older motors were 6202-C3, they are 15mm x 35mm x 11mm
Newer motors are 6203-C3, they are 17mm x 40mm x 12mm
C3 is the clearance on the balls.

The clutch/sprocket shaft on all take 6202-2RS sealed bearings.
2RS stands for 2 Rubber Seals.
Shielded bearings come in most of them, but I would recommend the sealed bearings.

All these bearings cost between $5 and $15 depending on manufacturer and where you buy.
Be careful that there are some specialty 6203-xx bearings that have oddball characteristics.
I was sold some at my local small-gas/lawntractor place that had 5/8" bores.

I just bought a tube of 10 6202 bearings from bocca bearings for $28. singular go for $4.60 or something so bulk price is almost half.worth it to me!

 

[Steve Best]

There is no need for "Z" bearings I believe.
While they might keep bits out if you have a piston or cylinder failure, they also impede the flow of air and oil which will lead to overheating.

While into your case: I drilled an oil supply hole to the bearing from the transfer port trough:

When I pulled my well worn engine apart I found the oil in and around the crank bearing baked from heat and lack of flow.

I have no proof this oil passage works to improve flow, but it is pretty much a standard feature in most Hi-Perf 2 strokes.

I don't know if I can recommend the epoxy recommendation on this picture.
I did it and it didn't seem to improve the piston port engine.
It may work better with a reed valve engine, but at this point I'd suggest don't wasted your time.

Steve