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giorgio67

PISTONS/RINGS PROBLEM....

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Hi guys,

start to check pistons rings gaps today.

Everything is fine with the compression rings on all pistons but while trying to fit the oil control rings I've noticed a big issue,

I have Mahle HC grade B pistons

I have SJ rings for 912 HC NA engine  from DEVES, these are 4 pieces oil control ring set-up.

So installed the EXPANDER first just to discover that there is no more space on the piston groove to install the upper and lower steel rails!!

The expander has no clearance in the groove so there is no way to install the other two rings and the SPACER-C on the groove.

Measured the groove and found that is 6.20 mm, my old LC pistons have a groove of 6.70 mm.....

Does anyone know the groove size for the 912 HC Mahle pistons?

The fact is that or I have a bad pistons batch or SJ sent me the wrong rings but how to check?

Also, the oil control rings from DEVES are pre-gapped at the factory and they dont need to be checked for gaps but I have try to see the gap of the two steel rails and these are totally out of specifications as reported on the manual, some rails have near 1.00 mm gap...?

Please help

Here the link of the Deves oil control ring set-up:

http://www.deves.com/oilring_inst.php

 

Thanks

Giorgio

 

here some pics of my pistons

do you see something wrong?

 

 

post-3419-0-31070000-1367151947.jpg

post-3419-0-63170100-1367151966.jpg

post-3419-0-41353400-1367151977.jpg

post-3419-0-96544300-1367151983.jpg

Edited by ghe67

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Upgrade today to remove Google ads and support TLF.

The groove size is 3.40 mm on the Mahle not 6.20 sorry for the mistake.

The lc piston has a groove of 4.00 mm.

Also, found that original Lotus oil control rings are one expander and a single ring, so what's the matter to use a four pieces control ring..?

Thanks

Giorgio

Edited by ghe67

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Hi,

does anyone know the correct parts number of the oil control rings for the S3 NA HC 912 engine?

On the parts list (S3 turbo) there is no mention about NA engine and I have not any reference to check, maybe are the same of turbo engine?

Thanks

Giorgio

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SJSportscars list for S3, Pre 1988 & 1988 to 1992: OIL CONTROL RING   A910E2195F

 

 

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HI John, thanks.

I saw them but they are completely different from mine and I would like to know the ring wideness to be sure they will fit my 3.40mm groove.

Giorgio

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Uhmm... so received an answer from SJ Steve about the rings.

He said that the stock he has it's perfect and that the oil ring gaps of 1.00 mm is normal...maybe for DEVES rings I hope...

he suggest to send back mine and he will send a replacement set to me but...Garry, very kind as always, told me that the DEVES rings are very very tight on the piston/liner assembly and he does not like them at all.

Also I made a mistake while trying them.

The two steel rails of the control rings don't needs to be fitted completely in the piston groove,  once the Expander is fitted they go over it, up and bottom not in contact with the piston groove bottom wall, the spacer go between the two rails.

This in fact is really a tight fit, I cannot see how can I put the pistons inside the liners with the compressor ..but I would try prior to send them back.

Other option are the OEM Lotus/Mahle rings set for 300 GBP... I don't know what is better to do.

Advices?

Giorgio

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Giorgio,

Under no circumstances force the piston in, if the rings are tight in the groove.

 

When I bought my pistons and liners from Lotus, I asked if the rings would need gapping, and they said 'no'. However, I still checked them and found that they did - albeit ring tend gap, and not groove gap as you are experiencing.

 

However, all ring gaps are very important - if there's little or no gap on a cold engine, there will be even less on a hot engine.

A tight ring will break very quickly, and extensive engine damage will follow. 

As a suggestion, keep the Deves compression rings, and just buy the Lotus OEM Oil Control RIngs separately - this should be more cost effective.

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Hi Paul,

sorry for my english technical terms but for rings-gaps-groove I mean that the rings are too thick to sit properly in the groove.

The rings gap are correct and abundant...so no problem here but as the rails go OVER the expander it would be difficoult to compress the rings also with a 1.00 mm gap as checked in the liners alone.

 

Here some diagram and pic I've found on a site about the DEVES rings and the same issue I have:

 

Black = Piston
Green = Spacer
Red = Expander
Blue = Rails

 

the guy comments:

Firstly the rings are very difficult to compress, secondly there is enough space for one of the rails to 'go under' the expander but not the the other, this doesn't seem right to me, Is my groove to big!  I've emailed Deves but not had a reply.

 

So he made the same error trying to fit them...as on the DEVES site is clear that the two rails can not go under or between but OVER it.

This will end with a such tigh fit that I think I will follow your advice to use the compression rings only and the OEM oil control set to be sure....my engine cost me a fortune and I don't want to risk anything.

Giorgio

 

 

 

post-3419-0-24665900-1367342140.jpg

post-3419-0-08234600-1367342149.jpg

Edited by ghe67

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Hi Giorgio, I understood what you are referring to, and apologies if my mention of ring end gaps caused any confusion.

However as I mentioned, would it not be possible for you to use the Deves compression rings and just buy some Lotus oil rings separately. That way you should have a resolution that is cost effective, and shouldn't require any trial and error.

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Unless you know for sure that the LC ring grooves are the same as the Mahle - I would cut your losses and use the correct Mahle rings.   One other thing to consider - Are you using HC pistons in an Iron bore?   In which case my advice will be wrong, as rings for a chrome bore, are unlikely to be conpatible with an iron bore.

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Hi Steve,

yes, I'm using Mahle HC pistons on standard iron liners.

For what I know there is no problem doing this.

Giorgio

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Giorgio,

It maybe worth checking out Tim Engel's advice on the use of Mahle's with Iron liners.

His detailed missive describes exactly the piston/liner clearances you need to have (about 0.006 (inches) IIRC).

 

I can't recall if this also covers the use of certain rings though.

 

Have you had the liners machined to suit?

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Hi Paul,

already had a chat with Tim about that, also Garry told me it's a common practice to use Iron liner and Mahle forged pistons.

The termal expansion is quite different but I have 0.13mm clearance in the piston/bore and Garry told me that is quite usual to have this gap mixing HC and LC parts, so no probs here, he told me also to keep the rings gaps as for HC tolerance NOT LC.

My liners comes from SJ and as I have grade B Mahle piston they are within specification as is (0.13mm), so I had been  lucky they does not need any rebore job.

Today I've finished to install con rods and rings to pistons in the correct way as reported on the Deves site, SJ email me and told me that the 1.00 mm ring gap for the oil rings, even if too big compared to the measure reported on the manual, is normal for the Deves ring, so I would trust him...

I will try to fit the pistons with the compressor to see how they works and if I would not happy with the Deves, I will buy an OEM set oil control rings.

Giorgio

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Hi Giorgio, looks like you've done your home-work on this.

 

I also understand that in some circles, the iron liner/Mahle piston combo is preferred in high performance applications.

 

Hope the rest of your build goes well!

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