Re-bore ?

[Martinaston]

I have a block that could do with some new piston rings but the machine shop is telling me that if i go up by 0.25mm for the rings then i have to fit new pistons that are 0.25 bigger as well
Is this true or has the guy just got his eye on an early Christmas present ?

[Dan318-is]

if you just need new rings you dont need a rebore, just a hone.

You only need a rebore if your bores are screwed eg if they are scored or have water deposits on them. you do not need a rebore if it is jsut your piston rings that need replacing.

new rings for an m20 ar 57.00 for full set of 6 from GSF.

[Martinaston]

The rings are slightly oversize that i need to fit but the guy is trying to sell me new pistons that are 0.25 bigger than the original's. I thought that you could just fit the new rings to the original pistons

[Dan318-is]

why do you need oversized rings?

if you have the normal bore and original pistons all you need is normal rings mate!

[Martinaston]

The guys telling me the bores are too worn because of the lip at the top, but if they haven't gone oval then i assumed that i could just hone it and fit new rings the next size up. But he then said i need to fit larger pistons as well. (and then failed to give me an exact price for them)
So is he talking out of his exhaust or do i have to visit the post office with a shotgun ?

[Simon13]

there no such thing really as "re honing" a bore, they just polish them i think. Wierd. I thought piston rings have to be the same diameter as the piston. no?

[Karan]

i believe rehoning the bore is reproducing te cross hatchings on the cylinder wall that help retain oil

[bigkev]

if you 've got a lip on top of the bore you can physically see or feel its knackered and will need a rebore there is no way around it so to answer your question yes you will need .25 bigger pistons and rings but buy them yourself as the pistons will come with the rings and gudgeon(wrist) pins complete and then you can take them to your engineer and he can bore it to suit otherwise he will just buy them and charge you a mark up

[Turbo-Brown]

There is such a thing as a re-hone. It's where they re-hone the cylinders without having first re-bored them

If the wear ridge is a bit on the deep side then you may well need a re-bore and as such need new pistons which I believe are about Ԛ£90 each for the Mahle ones.

Mabey get a second opinion or something, perhaps measure the bores at several points yourself.

After 200k though, my cylinders only needed a hone and then a set of rings

[kam-325i]

i believe rehoning the bore is reproducing the cross hatchings on the cylinder wall that help retain oil

That is correctamondo....

[Apal]

I would agree with the other posts. IF there is a definate lip at the top of the bore it is shot and needs a re-bore. You will then need a new set of pistons to match.

However, be carefull that the lip is not just carbon deposist etc. Clean the top of a couple of cylinders to make sure and also measure the bore if you can. It seems to be unusual for blocks to wear this much these days.

I replaced the head gasket on my Toyota Supra 2 years ago (210,000 miles at the time and still going strong) and there was no lip (just some crud) and the bores were 'only' at the top end of the wear limit according to the shop manual. Similar story for two M20 blocks that I have been recently playing with as well.

As ever measure twice, cut once...

[bigkev]

all depends on how the car was treated most engine wear takes place when cold if crap oil is used or not serviced often enough it will wear prematurely.if you have a ridge on top of the bore and you just replace the rings you risk breaking the top ring the first time you boot it because the old rings slowly wear with the bore taking a tiny amount off the top of the top ring as it wears and then you put new rings in which are ever so slightly thicker and thefirst time you red line her the top ring hits the ridge and cracks it and you can guess the rest its just not worth taking a chance for thesake of a few Ԛ£Ã”šÃ‚£'s