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Old 28-01-15, 03:32 PM   #21
nickh
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Originally Posted by Lee C View Post
(snip) With regard to the new piston rings that I intend to fit, they fit the grooves precisely, i.e. the outer face of the rings are flush with the side of the piston.
How flush - dead (probably ok), slightly under (definitely ok) or slightly over (not good)? + Are you sure you have removed all the carbon from the bottom of the ring grooves?

NHH
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Old 28-01-15, 04:45 PM   #22
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I guess a picture paints a 1000 words, what I meant is that I have no free gap in the depth of the new rings when fitted to the piston, i.e. the rings will bottom out on the groove.
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Old 28-01-15, 05:08 PM   #23
martinpaff
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Lee

I get that you are measuring those thicknesses, but what with?
Ruler? No good! Depth micrometer? Probably okay...
In which case, if the ring groove depth is 3.00mm (not 3mm) and the ring is 3.00mm then you will just about be all right. If you cannot measure to that degree of accuracy then you haven't got enough space for those rings.

I'm surprised that they are 3mm deep - are they not 3.175mm (ish) or 1/8"?

MP
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Old 28-01-15, 06:07 PM   #24
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D type compression rings are 1/8th, with a (I think?) 3/16th oil ring.

Pete.
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Old 28-01-15, 06:53 PM   #25
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Sorry, the 3mm was for illustration purposes only.
I measured the gap by just sloting the ring in the groove, (see pic) When it is slotted in as far as it will go, the ring is still flush with the piston wall.

(really sorry if this is simple stuff and I'm being incredibly thick but because this is all new to me I want to be sure I don't wreck the engine.

Thanks
Lee
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Old 28-01-15, 07:07 PM   #26
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You're not being thick at all - everybody has to start somewhere!

We ask difficult questions because we're very keen to give you the right answers, so that you don't wreck your engine...

Fit one ring to the (immaculately clean!) top groove of the piston. Press the edge of a steel rule down the side of the piston. Can you still (even slightly) move the ring? If so then everything is fine. If the rule is resting on the ring and it's trapped solidly then the ring grooves aren't deep enough.

MP
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Old 28-01-15, 07:29 PM   #27
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Quote:
Originally Posted by martinpaff View Post
You're not being thick at all - everybody has to start somewhere!

We ask difficult questions because we're very keen to give you the right answers, so that you don't wreck your engine...

Fit one ring to the (immaculately clean!) top groove of the piston. Press the edge of a steel rule down the side of the piston. Can you still (even slightly) move the ring? If so then everything is fine. If the rule is resting on the ring and it's trapped solidly then the ring grooves aren't deep enough.

MP
Handy hint for cleaning ring grooves - break one of your old rings in half and use the sharp edge to clean into the bottom of the groove.

It could be that the piston is badly worn undersize. How much slack is there if you put the piston down the bore (without rings fitted)? You can use a feeler gauge to measure the gap, you will need a set anyway to set the gap on your new rings.

Dan
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Old 28-01-15, 08:02 PM   #28
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Thanks for the replies, this is all very good stuff, I didn't think about the piston being undersize, that doesn't sound good. I will get some answers for you all tomorrow night.

Good little hint about snapping one of the old rings, I like that

thanks for all your help so far.

Lee
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Old 28-01-15, 08:17 PM   #29
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Another 'handy hint' here as well Lee, in this cold weather run the new rings under the hot water tap for a while (after you have gapped them etc) as they are less likely to break while fitting them to the piston.

Having said that, I see you live in Bournemouth so cold weather is something you wont know much about!!

Pete.
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Old 29-01-15, 08:28 AM   #30
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Thanks Pete!
It did dip to -7C last week, that's the coldest it has been for a long while.

Cheers
Lee
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