Cylinder sleeve rebore

[Quilty]

Hello fellas wondering if someone knows the answer to this question
I have just bought a set of cylinder sleeves grime Heiden tuning standard size. They came as 74 mm sleeves with the instructions to be rebored after fitting. The question is that is the standard bore exactly 75 mm to fit 75 mm Pistons or 75.00 something??

 

[Brew]

i think it's 75.016

 

[Brew]

I would just take your jugs with installed sleeves, pistons and rings to a machine shop and have them do the measuring and cutting if it needs it.

 

[TLCbobber]

A 75mm piston in a 75mm bore wouldn't offer any clearance, it'd be tight as a drill bit in the hole it's drilling.
Cylinders are typically made smaller bore then machined to tolerance after fitting, if it was correct bore before fitting then it might be out of spec somehow due to fitting. Brew's figure sounds about right, idk what it should be exactly other than 75+thou if the piston is 75

 

[TwoManyXS1Bs]

I would just take your jugs with installed sleeves, pistons and rings to a machine shop and have them do the measuring and cutting if it needs it.

Yes, this is the proper way to go about this. The machine shop needs to have your pistons 'in hand' to get the proper clearances. Take your service manual, showing the piston/cylinder chapter, with you to the shop. They can also set the ring gaps. After machining, keep track of which piston goes into which bore...

 

[Quilty]

A wise old man suggested that it should be 75 mm plus two thousands of an inch fit the Pistons with the rings and if too tight go up to three thousands and no more. Any truth??

 

[TLCbobber]

According to my manual on bore examination and measuring wear:
"If it is possible to insert a 0.004" feeler gauge between the piston (without rings) and the cylinder wall on the thrust side, remedial action must be taken."
This is, of course, for measuring bore diameter in lieu of an internal micrometer.

Assuming you use micrometer, it also says: "Measure the bore diameter below the ridge, compare this reading close to the bottom of the cylinder bore which has not been subject to wear. If the difference exceeds 0.005" it is necessary to have the cylinder rebored and fit oversize"... etc.

I still don't know what newly machined tolerance would be, but this kinda shows it's pretty close.

 

[TwoManyXS1Bs]

A wise old man suggested that it should be 75 mm plus two thousands of an inch fit the Pistons with the rings and if too tight go up to three thousands and no more. Any truth??

A bit generalist. The service manual explains it better.
Several of us here have performed cylinder boring.
Many more have had direct dealings with the machine shops.
The experienced ones will tell you that piston diameters aren't always precise.
That's why cylinders are bored to match the pistons per clearance specifications.

The 75.00mm, 75.25mm, 75.50mm, etc diameters are nominal dimensions, used for parts referencing,
and bragging rights...

 

[kopcicle]

posted elsewhere but ...

Although YammaMama says .002 to .0022 (and I agree) the hypereutectic alloys will tolerate much closer clearances initially .

The process was to finish the bore within .002" , finish to piston size with #220 and then create necessary clearance with the softer finer finish hone (approx #320) . Finish clearance could be as little as .00075 for smaller bores and a rch over .00125" for 3 5/8" bore (kinda gave it away there) . Initial start up and following heat cycles are a bit scary . I use time to temperature as a guide . Usually and somewhat scary is the engine will heat and slow down noticeably from the usual 2K RPM and shut it off taking infrared temp at shut off . After a full return to cold iron put a stop watch and a timer on the next cycle . After several heat cycles the time to temp will increase noticeably . At this point throw the break in oil away and reload , Go out and put increasing loads on the engine .
If you get it tight you're screwed . If you get it loose it never breaks in . If you get impatient it squeaks . If you tune to the edge of detonation you'll turn a piston into itty bitty pieces . If you get it right you have a build with great longevity .

Just some more virtually useless information


~kop

 

[Quilty]

Thanks for putting the shits up me kop. I have a machinist doin the work now as we speak so we'll see. when I first run the bike am i putting it under load or just at idle for the first temperature cycle

 

[member3480]

Each piston is different and most good piston company's will supply you with the bore size that recommend . Good machine shops use the 2000 rule if not stated. You have to take into count heat and expand as motor get hot. I have done many and yes if you check each piston not only are they different in size but weight also.