Piston rings

marinatlas · Feb 3, 2015

Hi, it happens to me too , with Hasting rings ........then I googled that , and found many people , mainly with cars , got same trouble , some of them trim the expander , some don't .....so what to do trim or fit asis, or buy another brand of rings ? which one fit the JCC , according the one piece , supplied sometimes is an easy fit but a real crap ......!

baz · Feb 3, 2015

i too had to shorten an expander ring on a special piston in a BSA b44 engine ,,,,,,,,,,,,,,,,,,baz

Hobot · Feb 3, 2015

If the bores are to spec ID and the piston ring lands profiled right then then rings sets should fit fine off the shelf so I'd complain to ring suppler to see if a better fit on hand before trimming. I've broken rings hand fitting and compressor band shoving with surprisingly little force applied just right, click. I now perfer to hand fit pistons into cylinder then lower on rods then slip pins through, if pin fit loose enough to allow w/o banging on them.

kerinorton · Feb 3, 2015

marinatlas said:
Hi, it happens to me too , with Hasting rings ........then I googled that , and found many people , mainly with cars , got same trouble , some of them trim the expander , some don't .....so what to do trim or fit asis, or buy another brand of rings ? which one fit the JCC , according the one piece , supplied sometimes is an easy fit but a real crap ......!

Sounds like a bloody bad sale pitch on the behalf of Hastings, as when you do have a problem, they will find out you have modified their rings and, they can legally walk away from the warranty.

Make the bastards supply the right parts or go somewhere else. They will argue with you over it but stick to your guns. They will appreciate your effort in the end. They may even learn to get things right [ that's provided they got things wrong in the first place ].

Would you continually run your tyres at say 10 PSI, or even 100 PSI. You wouldn't would you. Because if you did, and something went wrong, the tyre company could tell what the caused the fault in their product, and negate the warranty.

Never meant to cause offence, but I was offended by the comments referring to shortening expanders.
Dereck

Beach · Feb 3, 2015

Don't be offended Dereck....Everyone is not going to agree all the time....Nothing personal..BTW....Not sure about any warranty on ring sets..If there is, good luck with anything more than another set of rings...

Biscuit · Feb 3, 2015

The ring set last fitted to my Norton at .020" over were Hepolite as were the pistons. It was awhile ago and from reading here, apparently Hepolite rings have fallen out of favor because of quality issues. At any rate, the Apex style three piece ring had a pink end and a green end. You needed to see both colors to insure the ends were butted correctly as it was pretty easy to overlap them, however the ends were specially constructed to butt against each other and trimming them would have resulted in miss-matching ends that would never have butted squarely. Are Hasting rings not like this?
I also wonder why those who seem to feel it's fairly common to have to trim Hasting rings continue to fit them. This really seems like a quality issue.
One other thing come to mind though. Is it possible some of the after market pistons have varying ring grooves? A groove too shallow could cause an expander to become bound. Maybe it's not the rings but the pistons.

marinatlas · Feb 3, 2015

One other thing come to mind though. Is it possible some of the after market pistons have varying ring grooves? A groove too shallow could cause an expander to become bound. Maybe it's not the rings but the pistons
Yes , that could be the solution, as they were not the same brand, who is doing the "kwolity" control ............?

mkmachine · Mar 6, 2016

I've been putting together a 750 with +40 pistons and rings and it didn't seem right, so I looked up this thread.
I have a set of AE Rings, bought locally, who sourced them from Coventry. The gaps on all the rings are good except the expander ring. The expander rings just simply don't fit in the bores.
I don't know if I'm going to shorten them or buy new rings, but I thought I'd try and upload a picture

https://flic.kr/p/Epu1GH

rings by studio2434, on Flickr

Beach · Mar 7, 2016

On my 750 I had to trim that ring...It has caused no problems...My rings were Hasting but I guess this could happen with any ring set...As for the Hastings , I won't use them again because of this, they should be correct when you buy them...Just my 2 cents worth..

Biscuit · Mar 7, 2016

mkmachine,,,In your photo you can see that if you trimmed that expander to eliminate the right hand (smaller) tower you would have no pressure at all upon assembly. That whole piece is made to flex and compress within the bore ONLY when held captive by the two oil scrapers and consequently within the piston groove.

lcrken · Mar 7, 2016

Interesting topic. Not a problem I've encountered, but interesting. Googling "trimming oil ring expander" and "oil ring expander gap too big" brings up exactly the same question as this thread, on multiple related forums. Many of the discussions target Hastings rings, but not all. Mahle is another manufacturer that is mentioned regularly. The answers are all the same as here, and there is really no good consensus on the subject. Most posts are some variation of "DON'T TRIM THE EXPANDER.", or "I had the same problem, and trimmed the expander.", or "it's clearly a case of poor quality control. Send them back." Several cases of people concerned about the apparently too large expander, who finally decided to just assemble it and see, and it worked fine. Also some examples of people who trimmed the expander and had massive smoking problems, and some who didn't. I don't have any answers, just wanted to point out that you have plenty of company on this problem.

FWIW, the people who contacted Hastings and Mahle about their concerns seem to have received good support from them.

Ken

kerinorton · Mar 7, 2016

Here we go again.
La de la de da.

Biscuit is right.

lets face it. if you are not capable of fitting rings correctly, get a proper mechanic to do it for you.

I generally buy new piston sets, because they come with the right rings, and because both rings and pistons wear. If it a low revving car, like from the 50's or 60's our engine reconditioners used to machine the top ring grooves that wore, and new rings were fitted with a specially made spacer fitted on top of that top ring. If you fit new rings to worn ring grooves, the rings will probably bend and you will get blow by your breather and air filter wont cope with..

Its a no no with as higher revving machine so best to use new pistons rather than the old ones. They are cheap enough if you are worried about that. In fact new pistons are probably cheaper than the cost of machining the old pistons [ $300.00 NZ for a commando set. rings are half that ]. Why bother.

Dereck

Dereck

lcrken · Mar 7, 2016

We do seem to have hijacked Piero's original post here. Mea culpa too. He has new Hepolite pistons and rings, and as far as I can tell, is worried about using the rings, because he had one of the oil rails break in the past. I think he's asking if we think he should use different rings, and we haven't really answered that. Is that right, Piero?

My suggestion would be to use the rings that came with the pistons, and just be careful to install them properly, but what do I know? I've installed quite a few original Hepolite pistons with the original rings, with never a problem. But that was back in the day, and the design and quality might have changed since then. The only problem I've seen with Hepolites and rings was back when they had some pistons with narrow oil rings in shallow grooves, and some with wider rings and deeper grooves, and people sometimes mixed them up.

Ken

billet · Mar 10, 2016

It has always been a pleasure to read your posts, Ken.

Usually sensible and to the point, with all that experience you have(yes, there are many other good contributors here)

Sten

Madnorton · Mar 10, 2016

Apparently the advice from one UK vendor selling new Hepolite pistons that are made in the Far East, is not to fit the rings that come with them - use the ones they supply with them instead - says a lot for the latest Hepolite pistons!!

There are also many out there that get the re-bore done then get the pistons and rings - wrong way to do it as many of you will know. Even more worrying is that 'so called' re-bore specialists will actually bore without the new pistons and rings present, I would avoid these like the plague.

Danno · Mar 10, 2016

An expander pushed into the bore and held to the cylinder wall should have a pretty good gap as it is not meant to touch the bore in use, only establish the equivalent of lands for the oil scrapers. If it doesn't, it's the wrong part. You could get away with trimming it, but how do you know what the gap should be without the proper part to compare to? Sending parts back is a major pain, but nothing compared to re-doing your rebuild. If anything, it should be checked held tight to the circumference of the oil ring groove in the piston, where it should still show a slight gap for heat expansion. But, again, how much?

Biscuit · Mar 10, 2016

Danno said:
An expander pushed into the bore and held to the cylinder wall should have a pretty good gap as it is not meant to touch the bore in use,

Only part of this is correct. An expander should not ever touch the bore walls, however, if only the expander is pushed into the bore, it should NOT be able to be squared up with any sort of a gap whatsoever. If there is a gap, it is absolutely too small. The expander is a spring, if you will. The scrapers are not. The top and second ring depend their own spring pressure exerted against the wall to seal. The three piece (Apex) oil control system depends on the pressure exerted to the two thin scrapers to seal. This pressure comes only from the compressed expander. Think about it, It's called an "expander" not a "spacer". I actually wonder how many of these expanders are needlessly trimmed because they "don't fit" when in all likelihood the installer is inept. Our tires don't just jump onto the rims themselves either, are they not quite big enough?

Danno · Mar 10, 2016

Biscuit said:
Danno said:

An expander pushed into the bore and held to the cylinder wall should have a pretty good gap as it is not meant to touch the bore in use,

Click to expand...

Only part of this is correct. An expander should not ever touch the bore walls, however, if only the expander is pushed into the bore, it should NOT be able to be squared up with any sort of a gap whatsoever. If there is a gap, it is absolutely too small. The expander is a spring, if you will. The scrapers are not. The top and second ring depend their own spring pressure exerted against the wall to seal. The three piece (Apex) oil control system depends on the pressure exerted to the two thin scrapers to seal. This pressure comes only from the compressed expander. Think about it, It's called an "expander" not a "spacer". I actually wonder how many of these expanders are needlessly trimmed because they "don't fit" when in all likelihood the installer is inept. Our tires don't just jump onto the rims themselves either, are they not quite big enough?

Sorry, but I don't agree. The scrapers are made of spring steel and exert their own outward pressure. The expander is just a spacer and does not exert any outward pressure. If you look closely at the photo in a previous post in this thread, you can see the flared edges of the expander that catch one side of a scraper. The land of the oil ring groove catches the other. The underside is a mirror image. The reason oil rings do not have narrow grooves to fit the scrapers like the upper grooves fit the compression rings is the expander gives the oil a pathway to the drillings in the oil ring groove for the oil to drain back into the crankcase. Three-piece oil rings were designed to alleviate some of the friction exerted by one-piece solid oil rings.

Biscuit · Mar 10, 2016

With respect, all of that was wrong.

pierodn · Mar 11, 2016

lcrken said:
We do seem to have hijacked Piero's original post here. Mea culpa too. He has new Hepolite pistons and rings, and as far as I can tell, is worried about using the rings, because he had one of the oil rails break in the past. I think he's asking if we think he should use different rings, and we haven't really answered that. Is that right, Piero?
Ken

Hi Ken,
I keep using the New Hepolite and rings with which they arrive.
But I'd rather have a single oil ring like old GPM.
By the way, do you know the rings of Teikoku and MC?
Ciao
Piero

Piston rings

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