9 replies to this topic

[germini30]

Looking for rings for an early mg metro 1275cc engine in std size.
I've been in contact with fw Thornton but they couldn't help.
There are 2 compression rings and a 3 part oil ring.
The compression rings measure 1.55mm and the oil ring 3.90mm. The oil ring is 2.7mm deep, and fw Thornton say that the only oil rings they list are 3.7mm deep so they won't fit fully into the piston groove.

[Spider]

I'm pretty sure these take a Grant either P1280 or C1280. The difference between these is the P set is Plain Cast Iron and the C set have a Chrome face on the upper compression ring. Up to you which you'd like, just be sure the bore is finished appropriately and that you also run them in the right way. These sets have 3 compression rings and of course the oil control set, just leave out 1 of the compression rings.

I have been using these rings for a long while now and have been extremely impressed by them. They have a superior design Oil Control ring to the originals that should keep oil consumption down for a very long time.

Hastings will also have rings for them, their P/N is either 6802 or 4731 - you'll need to check (I think it's the former). These too are great rings, I have used a few sets of these when the Grant's haven't been available, without issue.

[germini30]

Cheers for the reply.
I was looking at grants online listing yesterday and found a few part numbers that may fir, one of which was the number you've mentioned.
I'm going to give the UK distributor a call now to see what they say.

[germini30]

Grant sizes are good. Only thing is my second ring has a step, which would act a bit like a scraper I guess and theirs is plain. But saying that I guess if the oil rings are better than standard that wouldn't matter.

[Lplus]

Grant sizes are good. Only thing is my second ring has a step, which would act a bit like a scraper I guess and theirs is plain. But saying that I guess if the oil rings are better than standard that wouldn't matter.

Second ring?  I've heard of the top ring having a step to miss the ridge at the top of the bore of a worn engine, but not the second ring.

[germini30]

Yes, top ring is tapered on the inner circumference, second ring has a step facing downwards. Then there's the oil control ring

[Spider]

There's a good many commercial ring styles. Some are designed for fresh bores, some for worn but honed bores and others that are a straight out re-ring (and I would suggest not wasting your time with the later);-

 

 

What I would suggest is important here is firstly, that they are designed to work as a Pack, so for you and me, just follow what ever instructions the manufacturer has available and you'll likely have good success. Be sure the Pistons and in particular, the Grooves are not worn and are 100% clean. Make sure your selected Machine Shop finishes the Bores to the Ring Manufacturer's recommendations. Check their Honing doesn't have a Uni-directional cut or boas to it, that usually occurs when their Honing Head is worn, but there can be other causes. This will cause the rings to spin and that'll wear the Piston Grooves in short time.

On assembly, check the Piston to Bore Clearances aren't excessive and the Ring Gaps aren't tight. Don't fret if they end up on the large size. 

[absx2]

Top marks for your very detailed answers as usual Spider.

I don`t suppose you have a picture of a bad hone compared to a good one by any chance ?

 

" Check their Honing doesn't have a Uni-directional cut or boas to it, that usually occurs when their Honing Head is worn, but there can be other causes. This will cause the rings to spin and that'll wear the Piston Grooves in short time.

 

On assembly, check the Piston to Bore Clearances aren't excessive and the Ring Gaps aren't tight. Don't fret if they end up on the large size. "

[Spider]

Thanks for your kind words there absx.

I'm not much of a photographer I'm sorry, so while I have seen them and tried to snap of meaningful pics, I've not done well on that front I'm sorry.

This is from one of my old text books though - it really shows a server case on Unidirectional Honing;-


 

 

Here is one I dd manage a photo of though with a different defect.

This one was bored too close to the finished size and didn't leave nearly enough for a Honing Allowance;-

 

I've put the red line around where in the photo / angle, you can still see the machining from the boring operation. It was right around this bore, but with my limited photo skills, that's just where it's most visible.


This one;-

 

 

I'd call that as very acceptable. The minor longitudinal marks are just from removing the boring head, nothing to worry about.

[absx2]

Excellent again Spider and thanks for putting in the time and sharing your huge wealth of knowledge on a daily basis.

I think we all enjoy reading your in depth answers on the forums, pictures say a thousand words and you certainly go the extra mile.

I`m pleased my blocks have all come back looking like your last picture