Cooper S conrods
Turbo Mini Forums

I am building a twinky conversion on a Midget block for an Austin A30.

The crank is a rare EN40B and the rods are AEG521 which I thought were Cooper S.

As it is a Midget crank it has 1.625" beg ends and I thought that the rods would be the same, but I had not checked until I came to fit them.

They have the 1.75" big ends of all the other 1275 minis

Can anyone explain this to me please ?

And if anyone has a set of Cooper S or MG Midget rods going spare let me know !

Or do I risk any of those aftermarket rods at £250 a set ?

That's very odd aeg521's should definitely be 1.625". As you say they are S rods

Is the number cast or stamped.

Numbers are cast.

Te only explanation I have heard is that it might have been possible that some forgings were machined differently - but I am doubtful that there would have been enough material.

they are different with the weight, but do the same job, but i have 2 midget rods spare pm me for details i will rake them out if you want them for a fair price

Thank you Steve but 2 will not do it I,m afraid.

I will bear in mind your kind offer.

In extremis I can break a complete Midget engine but that would be a shame.

I've a set of new un used Arrow rods, 1275 with S big ends,

absolutely no comparison to the Chinese stuff available, they weigh 495 gms with bolts ,£500 ,just in case your feeling flush


carl

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

excellent price,but im not that flush just yet.

nice that the TM crowd are so very helpful.

Another silly question I,m afraid.
Can I just knock the tops off the original cams with a grinder to avoid rod to cam interference ?
I don,t fancy trying an interrupted cut in the lathe.
Is it necessary to grind them right down ?

Knock the hard surface layer off all around with a grinder then just machine the lobes off in the lathe. you can get rid of a good chunk of the lobe this way too.

An interrupted cut is no big deal, just take small cuts until concentric

Thank you.

In the past I have broken the tip off a tipped tool when attempting an interrupted cut even on ally.

Good tip to grind off all the hard surface of the cams first.

Before you get carried away, an S based bottom end will miss the cam lobes, in fact I think some std cams will miss the 1300 rods.

Before you get carried away, an S based bottom end will miss the cam lobes, in fact I think some std cams will miss the 1300 rods.

Am I missing something here ? AFAIK there is cam to rod interference only with Mowog/Arden 8-port heads due to different valve order. With typical 5-port head cams there are no issues.

I haven´t ever heard about S rods with 1,75" big end. I can´t remember what the big end bore is but with bearings fitted it is 1,625" for STD size.

I once tried to machine the lobes off the cam for BMW 16V conversion with a lathe but the end result was not pretty. Grinding takes a long time if you do it gently.

Jukka,

the lobes are machined off so you dont have to bother timing in unused cam lobes,

Sorry to disagree with such experienced people but I did try rotating the crank and the new rods now fitted and there definitely was interference. I could always time the "old" cam to miss the rods but I will have enough trouble setting the BMW cams.

There are literally thousands of A-series engines fitted with full race cams and as long as they are timed correctly the rods and cam lobes will not touch each other. All this assuming we are talking about factory rods.

I am an old fart so naturally I do things the old way and time the cam

worth a check in case it saved you some ball ache dave! I was positive S rods should miss the cam, but its interesting that they dont in this case, what cam out of interest.


also I can confirm H beam rods miss, i gave them a good checking after I bust a belt and took out a set of 1300 rods and a cam,

Edited by Joe C on 3rd Jan, 2018.

I used to have a 970 S engine with Mowog 8-port head and 4 Amal carbs. That engine had the 8-port head version of the 649 cam. Even there there were no interference issues. 1275S definitely had, IIRC 2 rod bolts of the S rods need relieving. I am not sure whether 1071S engines did but with shorter stroke I doubt it.

Tadge, which rods are you using now ?

Jukka have you taken on board that I know that any standard cam will miss the rods IF TIMED CORRECTLY but I am building a twinky and don,t want to have to time the old cam as well as the new ones -just me I suppose.

Anyway it took me only 20 minutes with an angle grinder to make all 8 cams virtually circular and everything is now copacetic.

Joe the cam was am unknown supplied by a TM member just because I needed a slot drive and did not have one to hand

Jukka have you taken on board that I know that any standard cam will miss the rods IF TIMED CORRECTLY but I am building a twinky and don,t want to have to time the old cam as well as the new ones -just me I suppose.

Anyway it took me only 20 minutes with an angle grinder to make all 8 cams virtually circular and everything is now copacetic.

Joe the cam was am unknown supplied by a TM member just because I needed a slot drive and did not have one to hand

Yes, I read and understood you first post

It takes literally a couple of minutes to get the old cam timed. Just orient the crank and cam keyways correctly as per factory manual and you are close enough. Fine tuning is not required. But enough of that.

Edited by jukka on 5th Jan, 2018.

true, and i dont know why there isnt a timing mark on the aftermarket conversion pulleys to enable this to be done easily,

of course, if you whip the lobes off then you have the posibility of under/overdriving the oil pump, just a though

Joe please explain to me how removing the lobes can affect how the oil pump works. Surely it is just driven exactly as it was before ?

With no lobes you " could" change the tooth count on the pulley if you were so inclined.

Sorry just a random thought I had while typing,

David, I'm not sure if it is what Joe was getting at, and I'm not sure if it affects a K head conversion, but the timing of the camshaft also determines when the oil flows to the head to the rocker gear through the slot/hole in the front cam bearing and the flats on the journal. Whether it's relevant once the K head is on I don't know.

BUT, as an aside, on your Dolomite Sprint engine, exactly the same applies to the jackshaft, which is very poorly documented as it has no cam lobes so people don't think it needs to be timed (dizzy goes in afterwards so that can be timed independently), but get that wrong on the Sprint engine and the jets of oil that come out of the end of the rockers to feed the cam lobes, don't come at the right time and the cam wears very fast.....

Schrödinger's cat - so which one am I ???