21 replies to this topic

[matthew_leech]

exactly what i am after thank you!

i have already got my carb in peices and am currently making those modifications.

I can see why you were voter Mr TMF, very worthy of it too :)




i am afraid i ahve even more questions now......

here goes,

Pistons. There seems to be a massive range in the price you can get oversized pistons.
Are them some to steer well clear of? and some that can be reccomonded? bearing in mind this engine isnt going to be a screamer.

Thanks alot

[Cooperman]

The best production for your application is the AE 21253. Mini Spares number is, I think, P21253-xx, where the 'xx' is the oversize with +0.020 being P21253-20. They are an excellent all-round piston, sensibly priced, strong and capable of compression ratios of up to around 11:1 and revs of 7000 rpm.
Also, if I may mention it, make sure you get a steel-backed oil pump.
Do a thorough trial-build to check all measurements and to see where the piston tops come in relation to the block deck, then have the deck skimmed to bring the pistons right to the top. During the trial build I always use standard thickness thrust bearings, then change them as necessary to obtain between 0.002" and 0.004" end float. If you need any further clarification on this just ask.

[matthew_leech]

Bit of a thread revival, but it seemed silly when this one is already fully of the background information regarding my question.

I have bought the pistons that Cooperman recomends at +20

I also have twin 1.5 Hs4s matched to a manifold.
A Morspeed stage 3 head
Switune Sw5 cam to be used with 1.5 roller rockers
turbo clutch

I am currently in contact with Rob Walker engineering regarding;

rebore +20 to 1293
crank reground, cross drilled & tuftrided
centre cap milled to accept centre strap
everything to be balanced
new cam bearings
dill and tap for 11 stud head


however, I am unsure whether to have the crank wedged and knife edged as i cant have a lightened fly as it is A+

Any advice on this matter or personal experience would be greatly received.


Thanks alot

Matt

[Cooperman]

For a road engine a wedged and knife-edged crank is probably a bit of an 'overkil'. You can lighten the flywheel on the Verto set-up and I'm sure Rob Walker will advise on that.
It sounds as though you'll have a really super engine when it's all done.

[matthew_leech]

Thank you to everyone who has conti used to this thread and helped me decide on the spec of my engine!

Cooperman, thanks for that that Is what I was thinking but looking for information on that matter was pretty difficult to find.

With regards to the fly, I was led to believe that the A+ could not be lightened?

Thanks again

[Cooperman]

The A+ uses a Verto flywheel/clutch and the flywheel can be lightened as I did it on the 1990 Cooper I built. It's a bit difficult to explain but I took it off the front face behind the clutch towards the outer edge. I'm sure Rob Walker will just do it for you. Of course, you'll need to get the assembly balanced afterwards. Personally I don't think it's worth wedging/knife-edging a crank unless you are going to be using very high revs like over 6500 sustained, but others may disagree. You are unlikely to notice any real difference on a road car and even on a track it won't make much difference to lap times. An out-and-our race engine is another matter.

[matthew_leech]

I am already having the full assembly balanced anyway, so I will ask for this to be done too.

As I hope is obvious from the spec I am going for a torquey engine rather than chasing big bhp figures. So I don't think wedging and knife-edging will be worthwhile,


Thanks again