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MG Midget and Sprite Technical - 4 piston rings vs 5

Curious why the 1098 and 1275 appear to have been shipped with either. My '66 1098 was originally configured with a 4-ring configuration. When I assembled the engine this weekend, I realized that I had sourced 5-ringed pistons... I proceeded with the engine assembly, assuming that either is acceptable. However, the oil-assist scraper ring on the bottom (5th) were supplied as .20 but weren't sized correctly for .20 pistons and bore. I happened to have the same scraper ring from a .20 over 4-ring set that did fit, which I substituted after seeking some experienced advice. So much for distribution quality control.

Just wondering what the history is on the 4 vs 5 configurations.

BTW, I recall a thread where someone kept discovering broken rings after running the engine for a period. Given the brittle nature of these rings; I broke 3 of those bottom rings before I decided they wouldn't fit. Given that the scraper ring gap fits over a cog in the groove, it can only compress to the point that both ends of the ring butt against the cog, limiting how far the ring will compress. The proper sized rings would compress properly into the groove to slip into the cylinder. I can see where an overzealous individual might force the piston in and find out the consequences a few miles down the road :).




TS Smith

4 or 5 rings!
That is a lot of fricktion.
You might want to think about switching to a more modern piston with a nice low friction 3 ring set.
It realy helps with power and reliability.

No clue to why you have 4 and 5 ring pistons
Onno Könemann

What Onno said!
Deborah Evans

I want to say 4 rings was factory, and have seen photos of 4 ring pistons, ,, but havent heard of or seen 5 ring

The only thing I can imagine is for piston stability...how thick are the rings compared to the modern day 3 ring

Prop
Prop

I don't recall seeing A series 5 ring pistons but I am more familiar with B series. The 5 ring pistons sport 3 compression rings and 2 oil control rings, one of which fits below the gudgeon pin. They tend to be on the pinch bolt small end rods

Peter
P Burgess

Early A series (848cc and 948cc) I believe had 5 ring sets on occasion. As suggested, upgrade to modern pistons/rings...
James Bilsland

From Moss website:

BHM1162 RING SET (per piston), standard
Note: Suitable for 4 & 5 ring pistons
1098cc

HTH
Doug Plumb

Doug, I keep meaning to ask so I'll do it now or I've probably been told and forgotten - what does HTH mean?
N Atkins

Thanks for comments. I've come to realize that the "typical" suppliers in the US seem to present less information and selection than is available in the UK. This 5-ring configuration is a current offering and would be interpreted as the stock configuration. Where would you recommend that I order a complete set of pistons/rings and be done with it? I want the car to be a reliable daily driver. I'll take out all of the new equipment I have and try to send it back.

I appreciate your experience.
TS Smith

http://www.minisport.com/mini-spare-parts/Mini_Pistons.html

The only place i could find them now at a reasonable price.
I am sure the will ship to the US
Onno Könemann

Im a huge fan of british parts north west....awsome service, great people, and good price on parts.... And they give you hard candy in each shippment....haha.... google them, You will be happy you did.

Also I like minispares...pricy but a really great organisation with good standards...and lots of instock parts...and they do have lots of sales

They have even given me sales just because I asked, I found telling them my dog just died or it was my birthday worked the best for getting sales

Hahaha

Prop
Prop

Opps ....minispares is uk, minimania is there usa sister....so I meant minimania

Prop
Prop

Prop
Minispares is cheap!
I don't think there is a connection between minimania and spares
Onno Könemann

Prop, I called minimania; all he shows for the 1098 is 5-ring sets. Moss shows 4-ring sets; and Victoria shows both 4 and 5. I think I'll just stay with the set up I have; its' built.

Thanks.
TS Smith

HTH - Hope That Helps
Dave Price

Onno, thanks for the referral; I went to the link you provided and it looks like a 3-ring set for the 1098. Rather than just concede... I'll give them a call tomorrow and verify pricing and availability. The online ordering process indicates the pistons need to be back ordered; pending lead time, maybe I'll be patient and wait for the 3-ring pistons.

BTW, any idea whether there could be a noticable difference in performance?? Also, I assume they designed to 5 rings based on metalurgy of the era???


Trey
TS Smith

Dave, yes it did, thanks
N Atkins

minimania and mini spares are not connected financially, but they do share parts and part numbers

also, as it turns out, staff at minimania designed minispare's web site



Norm
Norm Kerr

This thread was discussed between 27/06/2011 and 29/06/2011

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