34 replies to this topic

[unburntfuelinthemorning]

What make pistons do people on here have experience of for small bore engines?

 

Which ones would you buy, which would you avoid and why?

 

 

[DeadSquare]

Are you asking about 848cc, 997cc, 998cc or 1098cc ?

 

Are you thinking of standard size or oversize ?

 

Are you going to use the engine for competition or simply day to day motoring ?

 

Finally, to answer your questions, I would buy 68,25mm ones, if they were available, and I would avoid ones that are too large or too small because they won't fit properly.

 

I hope that helps.  Lol.

[unburntfuelinthemorning]

998cc

 

Probably +0.020", maybe more.

 

Day to day motoring with a moderate performance increase over standard - say 998 Cooper type of output.

[DeadSquare]

Assuming that your Mini is an 80's or 90's and not a near the end of production engine;  for that sort of specification, the pistons are not going to be under undue stress, so for simplicity I'd go for Minispares fully floating plus .020" or plus .040" flat tops.  Although there are also low drag flat top pistons available, I'd avoid them because they use a press fit gudgeon pin which require a different con rod,

[BaronVonchesto]

be sure of what type of mounting your current pistons use, circlip or press fit. Press fit replacement pistons for the 998 are hard to come by.

[Cooperman]

I built a good 998 engine a few years ago for my Grandson. I bored it to +0.080" which gave a capacity of 1060 cc. I used Hastings flat-top pistons, a Cooper 'S' 510 cam (my Grandson found it in a box of cams I have!), a 12G295 gas-flowed head, an HS4 on a Howley alloy manifold, a 3-into-1 ex. manifold with RC40 exhaust and a few other nice bits. It was great to drive on the roads, gave 65 bhp at around 5700 rpm and had a 3.2:1 FDR.

 

After selling it about 7 years ago my Grandson has traced it to the guy to whom he sold it to and has just bought it back. I have to go to Scotland to collect it in a few weeks, bring it back to Cambridgeshire, re-restore it (it needs some work as it has been neglected, but has done very few miles) then ship it to Vancouver where he is now living. We will be putting it on 10" wheels and may fit Mk.1 rear lights.

 

This is the car which was featured on the BBC 1 TV show 'Car Booty' when we were raising money to build it in the first place.

[unburntfuelinthemorning]

Assuming that your Mini is an 80's or 90's and not a near the end of production engine;  for that sort of specification, the pistons are not going to be under undue stress, so for simplicity I'd go for Minispares fully floating plus .020" or plus .040" flat tops.  Although there are also low drag flat top pistons available, I'd avoid them because they use a press fit gudgeon pin which require a different con rod,

It's a 1984 A+.  So you're recommending AE/Nural pistons?  What sort of oil control rings do these use?

 

be sure of what type of mounting your current pistons use, circlip or press fit. Press fit replacement pistons for the 998 are hard to come by.

I can use either as I have both types of rods.  Minispares do pistons for interference fit pins.

 

I built a good 998 engine a few years ago for my Grandson. I bored it to +0.080" which gave a capacity of 1060 cc. I used Hastings flat-top pistons, a Cooper 'S' 510 cam (my Grandson found it in a box of cams I have!), a 12G295 gas-flowed head, an HS4 on a Howley alloy manifold, a 3-into-1 ex. manifold with RC40 exhaust and a few other nice bits. It was great to drive on the roads, gave 65 bhp at around 5700 rpm and had a 3.2:1 FDR.

 

That's the sort of thing I'm aiming for. 

 

Are Hastings pistons currently available?  What sort of rings do they use?

 

I heard three piece oil control rings are the ones to have.

[Cooperman]

I got my Hastings +0.080" pistons from Mini Spares. they are 3-ring type. Good quality pistons for a reasonable price. I don't know whether they are still available.

 

A 998 over-bored to 1060 cc is a better bet than a 1098 as it does not have the long stroke of the 1098 and it can really rev if so desired.

[Spider]

I've used Hypertec Pistons (these may in fact be the ones Cooperman is referring to ?) The finish, accuracy, quality and that they take imperial rings is quite appealing to me.

[Minigman]

I’ve heard good things about the Russell ones available through Calver ST. Not used them myself though.

[Cooperman]

I just looked and I can't see those +080 pistons listed. 

[unburntfuelinthemorning]

Right so we have:

 

AE/Nural             Possibly what Minispares supply

 

Hastings             Have 3 piece oil control rings

 

Hypertec            Good level of finish, accuracy and quality with imperial rings

 

Russell               Supplied by Mr Calver

 

I haven't heard much about the different rings used.  I'm particularly interested in why some oil control rings are better than others?

 

Also are these cast pistons as I don't really want forged ones.

[Spider]

Russell               Supplied by Mr Calver

 

These are in fact Hypertecs, only re-boxed and roughly marked up by 4 times.

[unburntfuelinthemorning]

Are all these pistons that have been mentioned cast pistons?

[DeadSquare]

I haven't heard much about the different rings used.  I'm particularly interested in why some oil control rings are better than others?

 

For hundreds of years, men shaved with a single blade razor.  Razors now have up to 5 blades.   ...   Why ?

 

A 3 piece ring tries to get 2 oil rings into the space of 1, but as oil rings have done a superb job for 50 years, the only reason, in my opinion, for fitting a 3 piece is because the bores need reconditioning;  and, jf 3 piece rings in a new bore cuts down the lubrication, the bore will wear more quickly, but that is just my opinion.

 

As a rough rule of thumb, pistons bought 'off the shelf' will be cast.

 

As you have a set of press fit rods, you could use minispares pistons.  I had heard good reports about them, and helped a local guy to build his engine about 5 years ago and it has withstood 5 years rallying.

 

I think that you are worrying too much.  A friend had an 850 mini van that did 1/4 million miles, most of them commuting from Bromsgrove to Bristol at 70+ MPH on the M5.