120 replies to this topic

[Cooperman]

AE pistons are now made in Germany by Nural, so the quality will drop as they only see it a s piston for 1275 63bhp engines....... so it was over engineered (

Yes, the old 21253 was a greatr piston and capable of running to some serious CR's and revs. However, presumably we now need to find an alternative for higher powered engines. The Karl Schmidt ones seem to be NLA. Maybe the Omega range will be OK or do Hastings do a piston for the 1275?

[1977 Loud_Mini]

Right to answer a couple of questions. The pistons that are currently in the block are the AE20659 which are listed as Powermax pistons on the minispares website and they have new rings. I will obviously be taking these to check ring gaps and also if they are in the correct 3 stage if you like intervals around the pistons.
I have located a cylinder head which uses 37/32 valves but are cut down slightly to 36.5/31.5 so am i right in thinking these will be sufficient. The head is also apparentely very well ported and well suited to the 296 cam and 1.5 rockers if wanted to add them.
I will be running higher octane fuel to keep pinking and detonation at bay. I was thinking of putting in a 3.6 final drive with the standard gearbox ratios and in time upgrade to a sc/cr one. But have seen cars running very nicely with a 3.44 final drive and keeping on cam between gear changes. I'm currently renewing the gearbox bearings as they were shot.
Maybe i won't put an ultralight flywheel on the car but i like the idea of revving up quickly and better throttle response.

Evan.

Edited by 1977 Loud_Mini, 04 November 2010 - 07:23 PM.

[MRA]

Evan the pistons you have will not last at anything higher than about 6500rpm...... and th ecam you have won't really start to work until about 4500rpm.

You really would be better off changing to Omega pistons or changing the cam to a 276.

[1977 Loud_Mini]

Evan the pistons you have will not last at anything higher than about 6500rpm...... and th ecam you have won't really start to work until about 4500rpm.

You really would be better off changing to Omega pistons or changing the cam to a 276.

Ah thats a shame about the pistons, i don't think i have enough in my budget with the other parts to afford the Omegas as much as i would like to have them. The 276 may be a bit to tame for me as my 998 had a 266 in it and felt just like my standard 998, so the 276 in a 1380 would feel like similar to what i felt in the 998 as the lumpyness/lairyness of the cam will be reduced the higher cc you go?
Would the pistons only handle 6500rpm because of the compression ratio?

[Cooperman]

What Martin is saying is that the pistons don't have the strength to allow the engine revs to get high enough for the cam to reach peak power. That makes the engine unable to perform properly.
Why anyone would want a 296 cam in a road going car is quite beyond me, and I've been driving modified Minis since 1961. I would not even have a 296 in a very hot international spec rally Mini where power is essential. I run a 286 in my 'S' and that falls-off the cam sometimes even in competition and on the road, even with a 3.9:1 diff it is really not nice to drive any distance. It seems as though you have evolved a specification without regard to the application, rather than evolve a specification for a defined use. At the sort of revs you are aiming to use, like 7000+, it won't last very long and if a piston lets go it could well scrap the block in a worst case.
A 296 cam in an engine which can only run within the rev range of a 276, like up to 6400, will not be as good as a 276 as the 276 will give its power and torque lower down.
To repeat, you seem to be intent on building a track-only engine and hoping to drive it in normal day-to-day use on the road and it's not clear why you want to waste all that money building such a 'fussy' and 'cammy' engine which you won't actually be of use for daily driving. It will virtually be a racing engine only, but with fragile pistons and a well-built 1275 with a softer cam and a nice head will be quicker overall on the road.

[MRA]

The 73.5mm Powermax pistons will be fine, used to run the AGSP cam from MED with mine, regularly to the 'P' in rpms at the bottom 7000rpm rev counter (thats about 8000rpms). Plus they've been in three different incarnations of the same engine over the last twenty years.

You may have been lucky with your set of AE pistons, however the new 20659's are no where near the quality of the old version if you want to risk it then that is fine, but the old asdage "don't gamble with what you can't afford to lose" springs to mind..

Peter, a 296 can be a fun cam on the road it wouldn't give you the best of service for an international rally where low down torque is also a requirement, however if built to a good spec using good parts they can perform very well, not to everyones taste....... but neither are SCCR's and loads are used in daily drives throughout the country / world.

[Flat6]

AE pistons are now made in Germany by Nural, so the quality will drop as they only see it a s piston for 1275 63bhp engines....... so it was over engineered (

AE pistons are now made in Germany by Nural, so the quality will drop as they only see it a s piston for 1275 63bhp engines....... so it was over engineered (

Yes, the old 21253 was a greatr piston and capable of running to some serious CR's and revs. However, presumably we now need to find an alternative for higher powered engines. The Karl Schmidt ones seem to be NLA. Maybe the Omega range will be OK or do Hastings do a piston for the 1275?

There's a lot of misinformation in the last few posts of this thread, but what I can confirm without doubt is that the AE pistons may have been rebranded Nural, but the pistons are made to the same spec, and to the same drawing as in the past. The quality won't drop because "they only see it as piston for 1275 63bhp engine". That's just nonsense.

AE was the OE supplier to BLMC, and the parts are still made in an OE facility to these drawings. (Incidentally, 21253 is also the "control" piston in the Mighty Mini's series, so is frequently used in anger with no reported reliability issues)

A number of Mini specialists are now selling pistons as "equivalent 21253" (the part number almost now being used as a generic term) and often selling their cheap imitation's with an AE ringset to lead the customer to believe they're getting an AE product. They aren't the same and I wouldn't fit them to my own engines (but sadly there are those misinformed unfortunates on these forums who will).

Another small point - 21253 has never had oil drain holes in the ring groove - always slots. Hope that clarifies a few things..

[1977 Loud_Mini]

AE pistons are now made in Germany by Nural, so the quality will drop as they only see it a s piston for 1275 63bhp engines....... so it was over engineered (

AE pistons are now made in Germany by Nural, so the quality will drop as they only see it a s piston for 1275 63bhp engines....... so it was over engineered (

Yes, the old 21253 was a greatr piston and capable of running to some serious CR's and revs. However, presumably we now need to find an alternative for higher powered engines. The Karl Schmidt ones seem to be NLA. Maybe the Omega range will be OK or do Hastings do a piston for the 1275?

There's a lot of misinformation in the last few posts of this thread, but what I can confirm without doubt is that the AE pistons may have been rebranded Nural, but the pistons are made to the same spec, and to the same drawing as in the past. The quality won't drop because "they only see it as piston for 1275 63bhp engine". That's just nonsense.

AE was the OE supplier to BLMC, and the parts are still made in an OE facility to these drawings. (Incidentally, 21253 is also the "control" piston in the Mighty Mini's series, so is frequently used in anger with no reported reliability issues)

A number of Mini specialists are now selling pistons as "equivalent 21253" (the part number almost now being used as a generic term) and often selling their cheap imitation's with an AE ringset to lead the customer to believe they're getting an AE product. They aren't the same and I wouldn't fit them to my own engines (but sadly there are those misinformed unfortunates on these forums who will).

Another small point - 21253 has never had oil drain holes in the ring groove - always slots. Hope that clarifies a few things..

So am i right in thinking the AE20659 pistons that minispares sell will be ok? I'm not sure if this is where mine were purchased from but the numbers cast into the top of the piston say: AE20659 STD BLD

[Flat6]

So am i right in thinking the AE20659 pistons that minispares sell will be ok? I'm not sure if this is where mine were purchased from but the numbers cast into the top of the piston say: AE20659 STD BLD

Yes, these will be absolutely fine. I've got these in my engine which is in a fairly high state of tune and has been powering both road and hillclimb cars for many years... Just make sure (if they're used) that everything is within tolerance.

[Flat6]

Oh, and just to add, mine's running a 286 cam. I found it the best compromise for hillclimbs, running a 3.9 final drive with 10 inch wheels. It's fun on the road, but only for very short journeys.

I'd echo Peter's comments above regarding cam choice. Think about the use of the car and the kind of roads you drive on, and build the engine/box to that. The nicest engine I've built purely for road use was in my Mk1 S, which was a 1330 using 21253+060 pistons, Minisport st4 head (from memory was 35.6/31) a 266 cam, twin 1.5 su's and a 3.4 diff with GT close ratio gears. It had a lovely spread of power, pulled from nothing, was quiet, refined and returned reasonable economy. It might not be a "fashionable" cam choice, but it was perfect for the use of the car.

[1977 Loud_Mini]

Thanks for your help. Regarding the cam that was in my engine when i bought it, i will keep it for now and see how i get on. I'm not going to be doing much town driving so thats not really too much of an issue.
Just wondering if anyone has had any experience with an AP metallic pre verto clutch (can be seen on minisports site) as i have just purchased an ultralight flywheel and backplate along with a grey clutch diaphragm with this type of clutch?

[MRA]

Interesting information, Flat6, however I have seen the difference between an AE piston made in the UK and the new NURAL pistons which apparently are no longer made in the UK but in Germany, I have seen a degredation in the gudgeon pin, and some of the machined surfaces are definately different, they obviously have been manufactured with different tooling, possibly different machinery even. But I will agree that the castings look like they came from the same moulding tools.

This only supports what I have been told about the location of manufacture, being in Germany now, however I agree it doesn't prove it. just supports it. but my supplier gets them direct from Federal Mogul who import them from Germany, are you also saying that these pistons are made in the UK and then shipped to Germany ?

Federal Mogul, are the holding company for Nural, AE, Payen, and a host of others.

[MRA]

A grey diaphragm is a little heavy for that combination..

[1977 Loud_Mini]

A grey diaphragm is a little heavy for that combination..

I was thinking the same, but the person i bought the parts from had removed them from a 1380cc race engine that had completed 3 races. I have read about that clutch working best with the grey diaphragm but could possibly be used with the orange one.

[MRA]

Are you talking about a cerametallic clutch plate (paddle type) ? if so then it will work fine with an orange diaphragm.

Clutches rely on several factors to work...

1) number of plates used
2) mean radius of the plate/s
3) clamping force... spring pressure...... or hydraulic pressure if its an auto
4) coefficient of friction

on a Mini no.1 tends to be pretty hard to change, no.2 is governed by the flywheel and or backplate, no.3 is governed by the diaphragm std, orange, grey, double grey etc.. no.4 is governed by the clutch plate material and the friction surfaces of the fltwheel and backplate, some materials will lower the resultant frictional coefficient.

Edited by mra-minis.co.uk, 08 November 2010 - 07:59 PM.