Rings don't fit the pistons... Pistons don't fit the rings..

[reynard]

I have a 71 Plus 2 mutt that came to me with a Tallblock conversion already done. The clutch slave (concentric) needed to be replaced, and one greasy dirty thing led to another and now I am in the middle of a frame off rebuild. One of many problems I have run into is that although the Tallblock kit came from Dave Bean twenty years ago, and that they were certain that they had a set of rings for it (I even sent a detailed, measured technical drawing of my pistons) and they sent a set of Deeves rings... the top compression ring will not fit. It is too thick.

I cleaned out the grooves with a chase, and even so gently filed those areas that were sticking, but the rings simply would not go into the groove all the way around on all four of the pistons. I placed them in the cylinders and checked the end gap, and it is perfect. My measurements show a .0620 top ring groove, and my old rings measured .0615, but the rings that came in the set were .0620 or thicker and would not fit. The piston are marked "FORGEDTRUE" and are 3.276" (at wrist pin) in a 3.289" (83.55mm) bore

I have to admit that I broke one of the rings attempting to check the fit (rolling the ring around the outside of the piston) so the idea of using the old rings looks better and better as my vacation time, set aside to finish the car, is evaporating and no solution from Dave Bean (he didn't have any idea what to do other than to grind off the necessary amount on a stone) is forthcoming.

The old rings only have about five hundred miles on them (and then twenty years in storage) so I am tempted to re use the top ring as they do fit and the end gaps check out.

Any idea of where I might find the correct ring set? Or any thoughts on using the old top ring? Or any idea where these pistons may have come from so I can track down some rings ASAP.

And no, I don't want to grind them down on a stone.

As always, thanks for your help and time. Elans don't run on gas, they run on favors.

Andy Anderson
Fort Worth, Texas US

[lotuselanman]

Hi,
Take the rings and pistons to an Engine Machinist and he should be able to machine the piston ring groove to suit.
This is not unusual.
Ask him to also ensure the ring depth is correct for the rings, would be prudent to get him to check all the rings and grooves. Cheap insurance.
Les.

[reynard]

Thanks. That was my first thought, but that assumes I have a full set of rings, which I don't, thanks to my hamfisted "test fit". I 'll keep it as a backup plan, as I was hoping to finish the engine this week while I am on vaction and the machinist I use (and trust) Arlington Automotive Machine, is backed up for a month. I am on the way to see about a set of rings here in town that are listed to fit, but who knows?

This is the first time in almost forty five years of building engines that I have had this particular problem.

Thanks again, I'll keep you all posted.

Andy

[Tonyw]

Andy,

If the original rings are OK that is they are not worn, chipped or broken then there really is no reason why you should/could not re-use them, you have three altogether, one assumes the piston to bore fit is OK so if your top rings are fine and you use the new second and oil rings I cannot see much risk for you.

Regards,

Tonyw

[reynard]

Tony,

I appreciate the advice. I think I'll head in that direction while I wait to see if other, thinner, top ring sets become available.

Take care.

Andy