New pistons in old bores

[Humph7ey]

I will be fitting a new set of pistons to old 2.73" bores that have a maximum of wear of 5 thou. There is a slight ridge at the top. I know I should be using ring dodger top rings but wondered if I can get by with beveling on a gringing wheel.

[stevieturbo]

[Boosted LS1]

A file would leave a smoother surface.

[RobXjcoupe]

As long as the bores are still round. Usually worn bores are slightly oval when measured

[Humph7ey]

I should have mentioned that it is not a high performance engine but a L head 1934 Austin That still has good bores but the pistons were totally knackered.

[gazza285]

Ridge reamer and a rehone would be better, unless you like the smell of burning oil.

[Humph7ey]

I am going to deglaze it before fitting the pistons. Just worried about the ridge and chamfering the top ring.

[DVandrews]

Definitely chamfer the top rings, on some older engines oversized rings are available which if correctly gapped can help with worn bores. 5 thou oversize may not be a problem for the compression rings, but the oil control rings usually have a lot less authority on the bore (depending on type) and may be compromised in oversized bores.

Dave

[dhutch]

Boosted LS1 said:

A file would leave a smoother surface.

It's a bit like trying to polish brasswork with a saw really isn't it.

[Humph7ey]

I have been advised to get ring dodger top rings or machine the existing ones.

[Boosted LS1]

dhutch said:

Boosted LS1 said:

A file would leave a smoother surface.

It's a bit like trying to polish brasswork with a saw really isn't it.

I was expecting a whoosh somewhat sooner then this ;-)

[Inline__engine]

if there is a obvious ridge you should be overboring and honing

[annodomini2]

Or if you specifically need the std bore for some reason, bored out and liners fitted.

[Humph7ey]

It had been relined and I have a new set of std pistons. Reboring is expensive here in France. If it does not run as expected then I will have to think again.

[gazza285]

I did mention a ridge reamer, do you not like that idea?

[Humph7ey]

It would be great if I had one but they are not so common in the UK. Anyway I have just machined a step in the top ring that will clear the ridge.

Edited by Humph7ey on Saturday 22 August 12:48