DixieTheKid
|
| posted on 5/11/11 at 10:07 AM |
|
|
Bore & Piston sizes
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
COS IT'S Worth IT
|
|
|
|
|
MakeEverything
|
| posted on 5/11/11 at 10:17 AM |
|
|
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.
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
|
|
|
DixieTheKid
|
| posted on 5/11/11 at 10:27 AM |
|
|
Thanks for the info, whats a honing block? I have a de-glazer, same thing?
COS IT'S Worth IT
|
|
|
MakeEverything
|
| posted on 5/11/11 at 10:40 AM |
|
|
quote:
Originally posted by DixieTheKid
Thanks for the info, whats a honing block? I have a de-glazer, same thing?
More or less the same thing, yes. One is more course than the other i think.
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
|
|
|
snapper
|
| posted on 5/11/11 at 10:55 AM |
|
|
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.
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
|
|
|
MakeEverything
|
| posted on 5/11/11 at 10:58 AM |
|
|
quote:
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.
Thats a good point. HAdnt thought of that, rather i was thinking of a lip right at the top of the cylinder.
[Edited on 5-11-11 by MakeEverything]
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
|
|
|
ncoll
|
| posted on 5/11/11 at 11:12 AM |
|
|
most new piston rings have the top ring L shaped or barrelled to avoid colliding with the wear ridge.
ncoll
|
|
|
DixieTheKid
|
| posted on 5/11/11 at 11:20 AM |
|
|
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]
COS IT'S Worth IT
|
|
|
daviep
|
| posted on 5/11/11 at 11:53 AM |
|
|
quote:
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]
To be perfectly honest you are wasting your time trying to take accurate measurements with a vernier caliper, so any conclusions which are arrived at
based on these measurements is more guess work than science in my opinion.
To get accurate bore measurements the bore needs to be measured at at least four places, top and bottom of the thrust faces (perpendicular to the
gudgeon pin) and same across the across the bore inline with the gudgeon pin. Highest wear may not be right at the top and your looking for ovality as
mush as wear.
The Piston needs to be measured in the same way, your looking for ovality as well as outright wear.
As per previous post if the new rings hit the lip then the ring and maybe the piston will be damaged also as above you can sometimes get stepped top
rings.
To do it right you need internal and external mic's, if you're really posh a dial bore gauge speeds up the process a lot. A set of
mic's from cromwell or chronos will not cost the earth and may save you the cost of a wasted rebuild.
Davie
“A truly great library contains something in it to offend everyone.”
|
|
|
DixieTheKid
|
| posted on 5/11/11 at 12:31 PM |
|
|
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?
COS IT'S Worth IT
|
|
|
Mal
|
| posted on 5/11/11 at 12:49 PM |
|
|
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.
|
|
|
DixieTheKid
|
| posted on 5/11/11 at 01:01 PM |
|
|
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.
COS IT'S Worth IT
|
|
|
britishtrident
|
| posted on 5/11/11 at 03:56 PM |
|
|
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]
|
|
|
Bare
|
| posted on 5/11/11 at 04:34 PM |
|
|
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 $$ for a set of pistons ? Are these somehow special or unique?
Best get a few more quotes, if going that route.
|
|
|
DixieTheKid
|
| posted on 5/11/11 at 04:59 PM |
|
|
quote:
Originally posted by Bare
There used to available a wrench driven (manual :-) "ridge reamer' of simple design and low $ cost.
Also a Flex Hone from http://www.flexhone.com/... welll doh!.. is a time proven truly Excellent hone ( affordable if bought direct) on a decent
condition bore mind you and yes, it's drill driven :-) and dead simple to use correctly.
Seriously recomended.
Seems an awfull lot of $$ for a set of pistons ? Are these somehow special or unique?
Best get a few more quotes, if going that route.
Its the Cosworth badge, ive looked all over the net, the cheapest option seems to be a set of 0.5 oversize Mahle pistons, rings, clips and gudgeon for
about £400. Could be money well spent! An least i know its done. I can even hand over the pistons and say hone to that please  Could put on old set
on ebay and get a few quid back may be.
COS IT'S Worth IT
|
|
|
snapper
|
| posted on 6/11/11 at 06:12 AM |
|
|
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
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
|
|
|
