10 replies to this topic

[croc7]

A friend is looking to get 50-55 HP, at the wheels, from a 1098 that he is building. He asked me if I thought installing a center main strap was a good idea. My reply was that unless he planned sustained high Rpm, one wasn’t necessary but couldn’t think of a downside for doing so. Welcome any comments.

[Dusky]

Fit hardened moly washers under the main cap bolts. Works better than a strap and considerably easier and cheaper.

[mini13]

I dont see the point of machining a load of material off of the strap, risking making it out of round and then bolting a lump of steel on that may or may not be flat.

 

I would either leave well alone or replace with a 4 bolt main.

[Cooperman]

I dont see the point of machining a load of material off of the strap, risking making it out of round and then bolting a lump of steel on that may or may not be flat.

 

I would either leave well alone or replace with a 4 bolt main.

Agree 100%.

For relatively low output engines such as proposed, there is no need for any reinforcing of the centre main cap.

It is a good idea to have a 1098 cc engine fully balanced as it makes it so much smoother.

It is easy to get well over 65 bhp from a 1098 without any need for huge revs and they are excellent road engines.

[Midas Mk1]

If you watch the med youtube vid it’s also to do with taking a stress riser out the cap.

If your there might aswell do it - cheap caps no, decent ones like the kad or med ones are the way to go.

[croc7]

The MED center strap video convinced me, I steered my friend in that direction. Good product, thanks for the tip.

[GraemeC]

Don’t forget a line bore is needed after fitting the MED cap

[PoolGuy]

The centre main cap isn’t the weak point of a 1098. Dusky’s suggestion is spot on imo.

[Midas Mk1]

Med centre cap doesn’t need line boring, it fits as any other cms except uses arp studs rather than bolts, it’s not a replacement main cap.

[GraemeC]

The MED cap needs line boring, the MED strap may not (although the standard caps can distort after machining and assembling with a CMS so it may still need boring).

 

As said though, for a 50-55bhp 1098 a CMS really isn't needed.

Edited by GraemeC, 27 August 2021 - 09:39 AM.

[Spider]

I really wouldn't be fitting a strap to an A Series Engine. They just simply can't make enough power no matter how much boost you may want to use, to warrant a strap. Fitting one on all but Cooper S Engines only weakens the cap, as a fair chunk of material needs planning off the cap to give a smooth surface for the strap to sit against and the strap, while might be adding material, is a separate part and so add no strength to the cap itself.

Certainly an increase of circa 55 HP at the wheels, that's only about a 15% increase in output from the engine and keep in mind, I don't think your friend will be on the loud pedal that hard all the time, ringing out the revs in every gear, even if he was, again, it's not warranted.

 

The only cause of broken caps I've ever seen on these engines had been from mal-adjusted clutches that over-throw. When first released in 1959, our Minis didn't have over-throw nuts (or even a thread for them), but by early 1960, they had them. I did come across a technical bulletin on this and it was an item the dealers were supposed to swap over when the cars came in for service.

I'd need to check to be 100% sure, but Matt Read (he's probably the top man we have in these parts) doesn't use anything but standard caps, with standard bolts, the only mod being decent washers, on boosted small bore engines likely putting out circa 100 Flywheel HP.