Oil control rings too big for bore

[Winterfield]

Hi all,

I bought some new piston rings from cruzinimage for my 400/4 (3 piece oil control rings). I've checked the ring gaps for all the rings in the barrels, and they measure up fine (usually .35).

When I try to install the pistons on the bench, I can't get the piston past the oil control ring. I've confirmed this by removing the other two rings, and can't fit the piston in the bore with just the oil rings.

It looks like the same problem mentioned here: http://www.sohc.co.uk/index.php/topic,12513.0.html

Their solution was to just use the old rings, which is certainly an option for me. But I'd like to understand if anyone else has come across this, and how they resolved it?

Cheers

[paul G]

How and in what order have you installed the three parts onto the piston.

[Winterfield]

Wavy center spacer ring first, then bottom rail, then top rail. Center spacer is butted correctly, and ring gaps staggered.

[paul G]

just a thought  back to plan 1 then

[Winterfield]

Yup, and a good thing to check... the first thing that I did when they didn't fit was hit youtube to see how I'd cocked it up

[SteveW]

I have just had a similar issue rebuilding the missus’s 1964 Vespa.
The new rings, even though they are the correct ones don’t fit.
Putting them in the bore to check the gap and they are perfect, however once they are on the piston you can’t fit it in the barrel.

I found that the new rings are thicker, ie the inside diameter of the ring is smaller so the ring sticks out further.

Checked with the supplier and they were the correct rings so no idea what was going on.

Luckily I have an engineer mate who managed to make a jig in his lathe and machined the inner diameter of the ring to the correct size.

Rings fitted perfectly after, engine runs perfectly.

[AshimotoK0]

Just had a similar issue with Genuine Honda in sealed boxes rings for my 500/4.. all rings were dead on the correct ring gap except one second compression ring which actually overlapped in the bore. So I had to get onother ring set. I calculated that the ring was in fact a +0.50mm rather than the correct +0.25mm

[Laverda Dave]

I'm going through the same problem at the moment with Hepolite pistons for the Triton rebuild. Namely the oil control ring. It fits perfectly in the bore and the gap is correct. However, once the spiral 'spring' if fitted into the Grove at the back of the ring it is impossible to compress the ring in the bore. It's not the piston but the spiral spring. The technical department at Hepolite (or should that be Wassel as that is who own Hepolite these days?) don't even respond to calls or mails!
Luckily the supplier who I bought the kit from is sourcing me some other German made rings as a replacement at their cost as they've had the problem before with Hepolite rings.
Hepolite are now only a brand name, the pistons are made by JCC in Asia for them.
Its very disappointing that Hepolite know there is an issue and do nothing to resolve it and instead are more interested in profits whilst leaving their customers to solve the problems without technical support or advice.

[K2-K6]

I'm going through the same problem at the moment with Hepolite pistons for the Triton rebuild. Namely the oil control ring. It fits perfectly in the bore and the gap is correct. However, once the spiral 'spring' if fitted into the Grove at the back of the ring it is impossible to compress the ring in the bore. It's not the piston but the spiral spring. The technical department at Hepolite (or should that be Wassel as that is who own Hepolite these days?) don't even respond to calls or mails!
Luckily the supplier who I bought the kit from is sourcing me some other German made rings as a replacement at their cost as they've had the problem before with Hepolite rings.
Hepolite are now only a brand name, the pistons are made by JCC in Asia for them.
Its very disappointing that Hepolite know there is an issue and do nothing to resolve it and instead are more interested in profits whilst leaving their customers to solve the problems without technical support or advice.

For your application Dave have you considered Mahle pistons? and if they are available in suitable match. Always  been very good quality.

Has anyone put a caliper across the ring land diameter to see if there's any machining discrepancy there that could cause the problem? The rings don't generally sit hard up against the internal diameter once installed,  so essentially floating on the piston and centralized by the bore.

[K2-K6]

For Dave, good discussion here https://www.accessnorton.com/NortonCommando/piston-weight.24435/  looks interesting within the British twins field.

[AshimotoK0]

Has anyone put a caliper across the ring land diameter to see if there's any machining discrepancy there that could cause the problem? The rings don't generally sit hard up against the internal diameter once installed,  so essentially floating on the piston and centralized by the bore.

On mine it was definitely the ring not the piston land ... when I inserted the ring into the bore there as a slight overlap.

[Laverda Dave]

Thanks for the info Nigel. The second article is very interesting, one of the contributors has a photo of a MAP piston in a Morgo barrel. I have a Morgo barrel to but having to use modified Hepolite pistons due to the squish band built up in the head by Dave Degans (Mr Dresda Triton) when he built the engine 20 years ago. I would gave fitted forged pistons if I could have found any with the crown height I needed, unfortunately I could only find Hepolite that had the dimensions I was after.
Intresting to come across the name Mahale pistons, I put one of these in my 500 Jawa speedway bike in the early 80`s and running a 16:1 CR. It went well around Wimbledon 👍.

[Winterfield]

Dave, I'd be interested in knowing what the difference is between the two sets of rings, if you manage to measure them. I tried to figure it out with my non-existent machining skills, but couldn't measure accurately enough to see exactly what was wrong.

I ended up just using the old rings - not ideal, but I just want to get this engine running while I rebuild a second engine I have (this time properly... I hope).