Hello peps,

Just starting to put my cossy lump back together but could do with a liitle help. I have a slight lip on the bores top and bottom on both of my blocks. I obviouslly know i can have it honed but with the price of pistons for a YB being about £500 for +0.5 i dont really want to spend out if i dont have to.

I have taken some rough measurements of the lip at the top of the bore with a digital variner caliper being 90.82 - 90.88 ish. This indircates a standard bore with ware. The pistons are obvioslly standard i think these where 90.82mm from new.

So my question is what can i hone out to without changing the pistons or cant i? I have also seen this it called a " Ridge Reamer " lol

I would think it would be fine with new rings. I wouldnt bother reaming the ridge off either, just use a honing block to re-hone the bores and thats it. The ridge wont hurt at all.

Thanks for the info, whats a honing block? I have a de-glazer, same thing?

quote:

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Originally posted by DixieTheKid
Thanks for the info, whats a honing block? I have a de-glazer, same thing?

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To contradict Richard a little, if the rings on the old pistons have worn or if you rev a bit higher than before then the new rings could hit the ridge breaking a piston land.
Remove ridge, light hone whole bore, measure bottom of piston skirt, measure bore, find piston to bore clearance limits.

quote:

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Originally posted by snapper
To contradict Richard a little, if the rings on the old pistons have worn or if you rev a bit higher than before then the new rings could hit the ridge breaking a piston land.
Remove ridge, light hone whole bore, measure bottom of piston skirt, measure bore, find piston to bore clearance limits.

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most new piston rings have the top ring L shaped or barrelled to avoid colliding with the wear ridge.
ncoll

Ok ive just nipped down to the yard to answer your question.

The skirts of the pistons i have measured as near as dam it 90.74 - 90.75mm. <- now corrected

I thought i would check the block again, bear in mind a only have a vernier caliper but i think the lip is approx 90.78mm and the warn bored is approx 90.82mm.

So i have 0.07mm tolerance?

Thoughts please.

EDIT: Pics


yb piston
Above picture shows the incorrect way to measure a piston lol

yb bore


[Edited on 5/11/11 by DixieTheKid] - Piston measurements

[Edited on 5/11/11 by DixieTheKid]

quote:

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Originally posted by DixieTheKid
Ok ive just nipped down to the yard to answer your question.

The skirts of the pistons i have measured as near as dam it 90.28 - 90.29mm.

I thought i would check the block again, bear in mind a only have a vernier caliper but i think the lip is approx 90.78mm and the warn bored is approx 90.82mm.

So i have 0.53mm tolerance?

Thoughts please.

EDIT: Pics


yb piston

yb bore


[Edited on 5/11/11 by DixieTheKid]

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Ok, so what is my best option? Take the block over to the engeering company, have them measure it and then make a dicision?

Because i took the block and crank over there today but then asked what i wanted doing with the bores i hit the stumbling block. Then the £500 pistons got mentioned i put the block back in the van and left them with the crank.

Say for instance the block measured at 90.85 and my pistons measure 90.75 could i get away with a light hone just to take the lips of off the bores and install new rings? What are the tolirances rule of thmb?

You would do better taking the block to an engine machining company who will have a measuring instrument that makes 3 point contact in the bore, to provide a precise measurement and should also have a honing machine that will give better results than an electric drill driven hone.

Yes sorry, thats what they are. Thay have all the specialist equipment for re-grinding, honing and all sorts of other stuff such as CNC cutters. My crank is being reground with them at the moment.

The main stumbling blocks to successful fitting new rings are the rigid at the to of the bore, the surface finish of the bore and oval or scored bores. There are other potential problems such as worn grooves (lands) in the piston and ring gaps but the these are less common.

While there is little you can about badly worn bore except re-boring unless the the bores are badly worn getting rid of the ridge by honing and ensuring the bore has the right surface texture to retain oil while the rings bed in is sufficient.

The classic description of the bore finish is a 45 degree cross-hatch but the really important thing is the finish (surface texture) requires to be relatively coarse so as it wets properly and retains oil while the piston rings bed in. a highly polished bore is death to new rings.

[Edited on 5/11/11 by britishtrident]

There used to available a wrench driven (manual :-) "ridge reamer' of simple design and low $ cost.
Also a Flex Hone from http://www.flexhone.com/... welll doh!.. is a time proven truly Excellent hone ( affordable if bought direct) on a decent condition bore mind you and yes, it's drill driven :-) and dead simple to use correctly.
Seriously recomended.

Seems an awfull lot of $$ for a set of pistons ? Are these somehow special or unique?
Best get a few more quotes, if going that route.

quote:

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Originally posted by Bare
There used to available a wrench driven (manual :-) "ridge reamer' of simple design and low $ cost.
Also a Flex Hone from http://www.flexhone.com/... welll doh!.. is a time proven truly Excellent hone ( affordable if bought direct) on a decent condition bore mind you and yes, it's drill driven :-) and dead simple to use correctly.
Seriously recomended.

Seems an awfull lot of $$ for a set of pistons ? Are these somehow special or unique?
Best get a few more quotes, if going that route.

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Found on the PEC site and as a guide only.

oring and Honing.
1. Boring should be carried out in several steps leaving enough material stock for honing to size (approximately 0.080mm/0.003”).

A very rough guide of 0.01mm per 1mm of bore width i.e. 90.8 bore 0.091mm clearance