Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - ARP Rod Bolts and Cam Clearance.

Hello all.

My engine is apart, cleaned and ready to go off to the machine shop and I am now doing a bit of research into the parts. All the research so far has suggested that ARP rod bolts are a worthwhile investment, however four of them need to be chamfered to clear the barrel on some camshafts.

So, I have a couple of questions:

Firstly, has anyone used a Piper HR285 billet cam with these bolts, and did they experience the clearance issues?

Furthermore, am I correct in assuming that if this needs to be done, it will need to be before everything goes to the machine shop, for balancing reason?

Thanks for any advice.


18V engine
piper hr285
Burgess FRBV head
R Howard

HI Richie

I thought the rod bolt fouling was the early angular split ones when using arp bolts.


Peter Burgess Tuning

Richie and Peter. I had this problem, on an 18V engine, when using a County brand cam of standard profile. The diameter of the shaft (areas where there were no lobes) was .035" larger than the original BL cam diameter. This was sufficient, combined with the larger head of the ARP bolt, to cause the two to interfere with each other.

ARP advised that the heads of the bolts could be carefully ground down to properly clearance them. By "carefully ground down" they stated that the head of the bolt should not show heat coloring from the grinding. Hence, a pan of cold water and a single pass on the grinding wheel between dipping the bolt in the water seemed to work just fine and the engine has been in operation for over ten years now.

Yes, it would be best to have the con rods balanced after the bolt heads have been modified. But, I did not and my daughter's car has run well since the rebuilt. I suspect this is because I took pains to balance the weight of the bolts when doing the grinding with caused minimal, if any, change in the balance of the big end of the rod.

Les Bengtson

That's interesting Les, the Piper blanks are quite narrow, saves money I suppose :)


Peter Burgess Tuning

hi i've ran into this before with stroker cranks
got over it by reducing the cam diameter it felt safer tto me than grinding the tops off bigend bolts
there would be a need for rebalancing as well after grinding the bolts off
also not relevent here but---
if running a high lift cam with a big stroker four lobes have to have a tiddle off the side of them to clear the side of the conrod near where the top of the bolt is
William Revit

It is a common problem when using the ATP rod bolts although mainly with the early slant rods. Just grind off the outside top corner of the bolt for a 060" clearance. These bolts were made for other engines and just happen to fit our MGs be it sometimes with a bit of a grind.
You can do it without losing strength. It comes up often on the MG Experience sight and is an easy fix. Denis

I have just measured a Piper cam at 0.865" diameter. OE Leyland Special Tuning cam 0.970" with one ridge at 1.015" exact centre between two lobes!!!


Peter Burgess Tuning

I have only once come across this problem and that was with a Piper 285 and the diagonally split big ends.

I generally use the very late conrods (without the balance pads) with high spec engines and ARP bolts and find there are no clearance issues with the billet cams.
Chris at Octarine Services

Looks like problem is with OE diameter cams Chris....especially the one with the ridge!

Peter Burgess Tuning

hi guys
on my last stroker engine i didn't use arp bolts for this reason ended up using std replacement bolts
it's not going to be revved past 6 1/2 so i'm keeping the fingers crossed there
still had to reduce the cam to .780 dia to get .40'' clearance with later straight cut rods and the std style bolts
i ran a 45 dellorto and then 2'su's on this thing before but going with a 50mm weber for a try this time
can't wait sold the midget that it was in and having trouble getting motivated enough to finish off a shell for another althou there is a t type frame there that keeps looking at me so the latest lean is towards that
i think willy
William Revit

Thanks for the replies (and the research!), chaps. I think on this basis I will suck it and see.

Peter - I need to give you a call this afternoon.
R Howard

This thread was discussed between 02/03/2014 and 06/03/2014

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.