14 replies to this topic

[Old Skool]

After finaly stripping down my 1380 engine to do a rebuild, and have found that it's got Innocenti type conrods (cast number 12G1298/9)

I can't seem to find much about them other than the fact that 'specialists' want a small fortune for them?

[danwebster]

Best rods you can get after cooper S rods. My brother used to run inno rods in his KAD motor until he bought the Arrow set he has now.

[Big_Adam]

Inno con rods are lighter and tougther than standard con rods. So they are rather good.

[Old Skool]

Not bad for nout then!

[Jammy]

I thought Inno rods were Cooper S rods? :S

[Big_Adam]

Theres a slight difference in a little I beam half way down the shank.

[Guess-Works.com]

Inno rods are similar to the cooper S but retain the 1.75" bigend journal, whereas Cooper "S" rods (and Midget) run a 1.625" big end.

[TOMMO0302]

I have a few questions as am contemplating building a spare engine just in case:

Are rods standard across the cc range?
If you were to get the cooper S rods, what do you need to get thats different to accomodate the smaller big end journal?
Anyone know what crank stroke the EN161 crank had?

Think thats it for now.

I also want to know about what internals are interchangeable between the A and A+ block, but pretty sure thats covered numerous times before so will get searching.

[mini13]

Rods...

there are 5 types of 1275 (big bore) rod,

Pre A+
A+
Innocenti
Cooper S
Midget (1275 not the 1500 thats a totsaly different engine)

The pre A+ and the innocenti are physicaly similar ( they have the big square bigend cap but the inno one is smaller) and weigh roughly the same ( the inno rod is a bit lighter) but the Innocenti rod is a higher spec steel i belive its EN19 rather than the EN16 of the Pre A+ rod

the A+ is lighter than all the other rods and made from EN15 and has rounded caps

the cooper S and midget rods are esentially the same except for the material, the miget rod is EN21 the S rod is En24, both have a 1.625" big end rather than the 1.75" of all the others.

The reason the S rod is smaller is all mini ends (850, 998, 997,1098 and S's) were 1.625 up untill the Material specs were downgraded in the 1275 engines, at Which point the 1.75" ends were introduced on the 1275's.


tomm

the 1275 1.75" rods are all interchangable, so thats a yes for A and A+

if you get S rods the crank needs to be reground/changed, also there is two lengths of S rod.

also depends what you mean by en16 crank? the small bore cranks were EN16...

all the 1275 engines (Including the S) are 81.33mm stroke

I'm not to up on the small bore engines so can't advise.

[TOMMO0302]

Cheers Mini13, very helpful!

To explain my questions etc, someone is selling some powermax pistons (71.4mm) on cooper S rods, the En16 was what he said was on the crank (i now understand that is the grade of steel as opposed to a part no.) and he said it would make a 1340cc but couldnt work this out based on Guessworks table...hence thinking that crank may have had a longer stroke to obtain the 1340cc quoted. Was just wandering if these would be a worthwhile investment or not but since you need special cranks and what not im thinking probably not.

[mini13]

No Worry's mate,

Rrom what you say it sounds like the crank was offset ground to make it 84mm stroke, with the 71.4mm bore that would make about 1340-1345cc

If your looking for pistons i'll let you in on a little secret...

http://stores.ebay.c...2QQftidZ2QQtZkm

the hypertech is a craacking piston especially for the price, also the minispares mega piston is very good too.

[TOMMO0302]

It was the rods that stuck out as opposed to the pistons to be honest. But if the A+ are lighter is it fair to say you wouldn't see any benefit from the 's' rods other than if you were acheiving very high revs?

Another question, the same person says that he used the same rods/pistons originally in a 1380 block before overheating problems, so got the 1340 block and used them just with different rings! Is that possible?

[Dan]

I don't think the maths works there.

To answer your earlier question, 998 / 850 rods are very different from 1275 rods of any type.

S rods are sought after primarily because they allow you to re-stroke the engine and are very strong.

[mini13]

theres no way he used those pistons in a 1380, 1380 pistons are 73.5mm full stop.

plus if they were used in an engine of a different size that means changing the stroke to get the new engine size, which means the pistons either end up sitting down the bore (meaning the block needs to be skimed, or the pistons stick out of the block (meaning they need to be skimed) if you went from a std stroke 1380 to an 84mm stroke then the pistons would stick out by....

84-81.33= 2.67/2= 1.337mm

All the A series rods are pretty damn strong, the A+ despite its lightness(from a strength point of view, I don't mean lightness is bad!) and inferior material grade, I've not heard of one breaking outside of racing (in fact i'm sure i remember someone using std A+ Rods AND BOLTS to over 9k rpm for drag racing), at the other end of the scale the S rod is pretty much unbreakable.

[TOMMO0302]

I actually ventured into the loft last night and found my 'yellow bible' that has been up there for about 8 years, i read that even the A+ rods with the inferior grade of steel are still over-engineered for purpose so rods are now not a concern to me. They went for £97 with the pistons by the way.

And i didnt think the Math worked out either!