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MG MGB Technical - Cylider Hone?

Hi,

Is there any need to hone a cylinder when fitting new rings if a cross-hatch pattern is still clearly visible on the bore? The engine has done about 30,000 miles and there has no wear ridges in the cylinders.

Thanks,

Steve
Steve Postins

If crosshatch lines are still visible after 30K miles, I don't think the previous set of rings ever seated correctly. Honing is done to actually leave raised, nearly microscopic pieces of metal that the rings sort of rearrange to create a seal. I would rehone them.
Ken Lessig

Ken's correct. If you're replacing rings after 30k and there's still crosshatching there then they certainly didn't bed in. Did you still have oil loss after your last hone?

I think you probably used synthetic oil on your run-in period. You need a thin mineral oil (preferably a running in oil). You will need to really hone it well to remove the problems created before.
Stuart Robson

Hi Guys,

Thanks for the comments. I should explain that I'm having to replace a piston after stupidly damaging the skirt whilst changing the cam (an embarrassing lesson, if you try to lock the crank with a block of wood whilst undoing the crank pulley, make sure the pistons are well out of the way). It's an overbored engine and compression has always been good (170ish) with no oil use.

I didn't have the car until it had covered 15K so don't know about the running in, but in view of the crosshatch still being very present (you can just feel it with your finger nail) how about just using running in oil for 500 miles to bed everything in fully and save taking out the crank (time is of the essence)?

Regards,

Steve
Steve Postins

Compression sounds OK to me and no oil use so I'd be inclined to go for what you suggested. If it doesn't work you could always hone it afterwards...It's a bit risky but if "time is of the essence" You're only changing the rings on one biston, yes?
Stuart Robson

That's right, the other rings are staying in place for the time being. I could really do with getting the car running again before my wife pulls the jack away whilst I'm under it. I have just spent a few weekends going through the whole engine rebuild process with my Roadster, and I don't think she bought the "I'd best do the GT whilst it's fresh in my mind" line!

Thanks,

Steve
Steve Postins

Steve,

I would fit the old piston rings to the new piston and leave the bore alone - make sure they are in the same ring grooves and the same way up!

It is not uncommon to still see the honing marks - especially if a honing tool rather than stones were used - the tool is a whole bunch of carbide burrs on a sort of squashed up chimney sweeps brush. These leave deeper marks and you can have perfectly seated rings even with the marks still visible.
Chris Betson

Thanks Chris,

I'll try to get the old rings back from Oselli - they're balancing a new piston against the old for me at the moment.

Best regards,

Steve
Steve Postins

I've seen crosshatch on 100000 mile motors, if they are put together right and the oil is changed every 3K this would be normal, not odd. Use new rings do a light hone you are on the road.
Ric
Ric

Steve:

Ric is right on all points. Cross hatching can still be visible in engines with lots of miles and the proper oil changes. You MUST do a light hone, or what's called glaze breaker, to remove the practically invisible varnish coat on the cylinder walls. Otherwise the rings may not seat properly.

G'day
Blake

You know what they say! (There's no place like Hone!!!)
Bob Thompson

This thread was discussed between 20/02/2003 and 22/02/2003

MG MGB Technical index

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