4 replies to this topic

[minigray]

Hi all,

I'm carrying out a full strip down & rebuild of a 1980 850, which has been sleeping in the garage for a while now… I need to replace the piston rings - standard size (62.9mm) which MiniMania doesn’t appear to stock anymore. I found out that the 948cc engine used in the A35, A40, Morris Minor, etc also has the same bore but a longer stroke.

I'm guessing that I can use the piston rings from the 948, but does anyone know if the 948 pistons are the same spec as the 850 ones?

Many Thanks

Gray

[Cooper-202S]

"I'm guessing that I can use the piston rings from the 948, but does anyone know if the 948 pistons are the same spec as the 850 ones?"

There are a lot of years between the 948 and your 850, might be worth speaking to FW Thornton in shrewbury, they seem to have pistons and rings that no one else has and were very helpful.

Nice to see someone giving an 850 a new lease of life.

[mini7boy]

Hi all,

I'm carrying out a full strip down & rebuild of a 1980 850, which has been sleeping in the garage for a while now… I need to replace the piston rings - standard size (62.9mm) which MiniMania doesn’t appear to stock anymore. I found out that the 948cc engine used in the A35, A40, Morris Minor, etc also has the same bore but a longer stroke.

I'm guessing that I can use the piston rings from the 948, but does anyone know if the 948 pistons are the same spec as the 850 ones?

Many Thanks

Gray

have you had a machinist inspect the block and tell you that it can still use standard size rings?
if not, you need to have such an assessment made.
does your budget not allow installing oversize pistons/rings?
have you checked other sources? Mini Mania is hardly the be all and end all.

I don't know if pistons from another A-series engine, like those you mention, will work, but it's worth checking.
Engines with equal bores but different strokes usually have different pin heights in the pistons to compensate. This could be a problem in using different pistons.

As a last resort, you might also consider contacting one of the custom piston manufacturers. They are able to stock/order rings strictly by size without respect to type/size of engine.
If you can get them the exact bore size and ring dimensions and other specs, you may be able to purchase rings that way. To save time, you might have to ship one set of rings, along
with intended bore size, to the piston manufacturer so that they can match them up.

I'd be surprised, though, if you cannot find a source for the rings elsewhere although you may have to buy a set of pistons in order to get the rings.

[Cooperman]

I know where to lay my hands on a set of original +0.030" pistons and rings for an 850. They are brand new and in their original box.
PM me if you are interested.

[DANTOO]

I checked the ring gap yesterday on the 850 im redoing, and its supposed to be a max of .30 of a mm ish cant remember the exact figure without looking, yet I managed to fit a 1mm feeler into the gap? ....and that was with the ring at the very top where they dont reach to wear the bore..... any ideas?

p.s the engine has done a genuine 33,000 miles. all other components seem spot on.