7 replies to this topic

[The Principal]

Wanted to share my experiences of uprating standard main caps from standard to the new generation of steel caps particularly the MED 4 hole Centre cap, nothing new I hear you say but there are some hidden issues to consider before shelling out your hard earned money.

So I am not going to debate the rights and wrongs of the purchase that's for you guys to decide but to comment on the work involved and give an idea of the costs associated.

Current MED Charges -

Centre Main Cap - £80 plus P&P
All 3 main Caps - £200 plus P&P

Focusing on the centre main cap for this topic, the kit comes with new bolts, washers and of course the new cap, first impressions are very good. To install the new centre bearing cap the block will need to be drilled to accommodate the additional two bolts, straight forward machine shop job at first glance however......

and this is where it gets expensive........

First thing to say is the MED kit is first class and highly recommended

To drill two additional holes and tap for the new main cap - £80 (all these prices are my experience at today's rate)

Now here's the twist and I rang all the usual Mini suppliers in the South and they gave a similar quote to be fair - the dreaded LINE BORING costs, once you have installed the new cap/s the alignment has to be spot on reason being when the crank is installed with the shells any misalignment could bind the crank and or prematurely wear the main shells or worse. The rates for line boring in my experience are based on the potential wear and tear to the machine shop cutters circa £160 upwards.

Your probably thinking hmmm this is adding up and yup your right but there is something else to consider - the timescales for all this work. Again in my experience the best machine shops are very busy especially this time of the year when Racing teams are preparing their cars so allow plenty of time for the work to be completed (2 weeks-ish) - its the old adage quality suppliers are always busy and charge the going rate.

So far we have new holes for the main cap bolts and the alignment is fine following the line boring, what about your crank thrust washers I hear you say? well the thrust faces on your new shinny centre cap may need machining too and that's another £65.

in summary -

MED steel Caps excellent
Timescales - longer than you think
Costs - plenty
Results - amazing, crank spins without effort

There are other options - A centre strap which saves on the line boring costs but check your gearbox webbing clearance as the MED kit only just clears my A-Series box by a fag paper

I am confident that someone will post a comment about how they can do the work cheaper and that's fine but bear in mind a quality job costs.......................

Hope this helps

TP

[MRA]

2 points, the cost for line boring is due to the setup, it has to be very accurately aligned, as you are taking so little out of the caps and ideally nothing out of the block.

Any modifications to main caps will at the very least need to be checked for alignment and roundness ! Including fitting a main strap.

[The Principal]

MRA - absolutely agree and the results are stunning when done riight

[MRA]

They are, but lets keep it a secret shall we I have heard of lots of people building engines with a centre main strap without even checking the roundness let alone the alignment etc... :-(

[MRA]

Including fitting a main strap.

You don't fit a main strap to a 4 bolt centre main...........

Not really sure what you are asking but nonetheless I'll answer it the best I can.

That is true, however you can fit a centre main strap to a standard main centre cap, modified to suit, however my point is still valid, the bearing MUST be checked and rectified if any irregularities are found, unfortunately most people will not have the required measuring equipment to do this and it is best left to a capable machine shop.

Edited by mra-minis.co.uk, 25 March 2013 - 09:08 PM.

[Cooperman]

If you need a 4-bolt high-grade steel centre main you are clearly building a very high-performance engine, so a few hundred quid for a quality job is unlikely to be an issue.

[MRA]

That is certainly true

Edited by mra-minis.co.uk, 25 March 2013 - 11:39 PM.

[Cooperman]

There is an old Mini tuning book by the late Clive Trickey. in it he describes how to fit a centre main bearing strap and that a 0.003" 'pinch gap' should be allowed at each end of the strap by machining the cap down to give that step. If you do this, when the bolts are tightened it 'pinches' the main bearing and stops the crank from roataing properly.
When fitting a main bearing strap, the cap should be machined and ground flat across the top so that when the strap is fitted it simply adds to the total depth and thus reduces distortion. Any tightness in rotating the crank must be investigated thoroughly or main bearing failure will be likely.
As Martin and others say, if fitting a high-grade steel main bearing cap the main bearings must be line honed and it is advisable to machine a small amount off of the other two caps and have all 3 line honed to ensure concentricity and accuracy of bore diameter. In particular, the main bearing bore accuracy can be a bit 'iffy' on the late cars, especially the MPI's.