18 replies to this topic

[grahama]

Hi,

I have had a look at the rings and was wondering what the end gap should be





I take it I am measuring it correctly ??

What are the problems if it is too big or small ??


Thanks,

Graham

[Cooperman]

Ring gap shold be a minimum of 0.003" per 1" of bore diameter and a maximum of 0.006" per 1" of bore diameter. Too small and it could close right up and snap a ring when the engine gets really hot. Too big and it can reduce the compression seal and lead to 'blow-by'.
Yes, you are measuring it correctly.

[grahama]

ok, based on the fact that my gaps are just over max, ( middle rings 3 tho and top rings 6 tho ) I might need some new rings. However the rings I have are non existant.

this the top ring profile



middle ring profile



I can find rings to fit my pistons but the profile is totally square, with no bevels. Does this matter ???


Graham

[Cooperman]

Don't quite understand the gaps you have. At 0.003" per 1" of bore diameter, the min gap shound be 0.009" whilst at 0.006" per 1" of bore dia the max gap should be 0.018" (based on calling the bore 3" dia.
Before re-fitting with new rings the bores must be honed. New rings are available from F.W. Thornton of Shrewsbury if ou give them the piston part number and bore size (standard or overbore size as stamped on piston top).

[grahama]

Hi,

just measured the bore diameters and they are 2.539", (standard bore diam), therefore multiplied by the max .006 it should be 15 tho ish max. I have given the bores a deglaze/hone and I have 21 tho on the top rings and 18 tho on the middle rings.

The pistons are proving difficult to find rings for, (flat top circlip 20528 G49A), FW thornton didn't recognise them !

I don't have the spare cash to buy a full piston set up and am thinking of putting them back in and praying !!

How bad is a bad end gap ?

Thanks again,

Graham

Edited by grahama, 17 January 2012 - 09:05 PM.

[Cooperman]

0.021" is a bit of a large gap really. I wouldn't want to re-fit those. Check the gap about 3/8" down from the top of the cylinders and again at mid stroke. Is the gap the same? If it's greater at mid stroke then the bores are very worn and you do really need a re-bore and new pistons. But, if you can't afford to do the job, then you really have no alternative but to re-fit what you had and hope it will not burn too much oil and will perform OK until you can do an engine build.
Good luck with it all.

[dklawson]

Also, when making the measurements be sure you use a piston to push the rings down the bore so they are inserted "square". If the rings are not fully perpendicular to the bore your readings will be off a bit.

That said, when I bought my last set of AE pistons about 5 years ago the gap was close to what you measured. I was not happy about it but used the rings supplied with the pistons and have not had any ill effects.

[Cooperman]

Doug, do you think that ring gaps have increased 'as supplied' over the years. I can remember in the 60's and 70's having to linish a bit off the ends of rings to get sufficient gap. I've not had to do that for years. On the 21253 pistons I recently fitted to a 1330 engine (newly bored and accurately done) the average gap was about 0.015".

[grahama]

Will try again tomorrow and test all the way down the bore with the piston as a guide. Should everything be oiled up first or is it better to do it dry??

Graham

[Cooperman]

Will try again tomorrow and test all the way down the bore with the piston as a guide. Should everything be oiled up first or is it better to do it dry??

Graham

It doesn't really matter so long as, as Doug points out, the rings are absolutely square in the bores at each position measured. Use a piston to push the ring down the bore once you get the ring into the bore.

[bmcecosse]

I would just use them - but surely the stepped ring is the TOP ring - designed to be a 'ridge dodger' ?? Be sure to space the gaps out round the circle by 120 degrees from each other.

Edited by bmcecosse, 17 January 2012 - 11:44 PM.

[Frisco]

Its apart now so why not do it right?

If the bores are not new they may be oval and you would need an internal mic to check it properly. At least push the rings down further in the borse and measuer the gap there rather than at the top

[dklawson]

Doug, do you think that ring gaps have increased 'as supplied' over the years. I can remember in the 60's and 70's having to linish a bit off the ends of rings to get sufficient gap.

I only worked on a couple of engines back in the 1970s as those were my teen years. At the time I did not have any tools to speak of so I had the machine shop check the ring gaps and even fit them to the pistons for me. So I don't know if there is a trend for looser gaps or not. Larger clearances on components are a fairly common practice now to minimize frictional losses and gain fuel economy.

Over the years several people told me how to sand/file the ring gaps and what to hold them to. I remember being surprised that I did not have to sand/file the ring gap wider on the Mini with the 21253 pistons. At that time I wrote K. Calver to ask his opinion on the gaps I measured. His advice was the same as Roy's... since this was a street engine, just run them.

[Cooperman]

A guy I know raced in a one-make category (not in a Mini) and they had to use all standard components. The get better compressions without cheating, they used to fit rings from +0.020" oversize to standard bore pistons, setting the gaps to 0.002" for each 1" of bore diameter.
I've used some rings for competition from a company in Phoenix, Arizona, called 'Total Seal' rings. These have a 'gapless' 2nd ring and certainly improved performance and reduced oil consumption. I fitted them to Karl Schmidt pistons which were at +0.020" oversize.

[bmcecosse]

Blimey - KC and I have NEVER EVER had the same opinions...........