Fretting on main caps. Scrap or cross bolt?

wesbrooks · Post by **wesbrooks** » Sun Sep 25, 2016 6:11 am

Hi.

I'm going through the process of cleaning and inspecting an interim 95 3.9 serpentine engine. I can see signs of fretting and one of the caps drops right in with no force, but doesn't rattle or slide once in. Engine is from a discovery.

Plan for this lump is a torquey cam (still destined for a 4x4) and use it as a base for mega squirt development before a more performance related build in 4 or more years time.

My question is will nut and stud and cross bolts save the block or is signs or fretting terminal?

wesbrooks · Post by **wesbrooks** » Sun Sep 25, 2016 6:14 am

It's being built for an auto instalation and currently has the standard lucas fuel only engine management with a dizzy.

sidecar · Post by **sidecar** » Sun Sep 25, 2016 8:47 am

I'm sure that there are many engines out there that are runing with fretted mains, at the end of the day it would be better if they are not fretted but I think if you fit a stud kit it will be OK. If the block will take cross bolts then drilling it for them would be even better. If you go for studs then there is more debait on the torque setting to go for on the nuts.

wesbrooks · Post by **wesbrooks** » Sun Sep 25, 2016 9:01 am

Thanks. If drilled for cross bolting does it force the need for a line bore?

So studs and not over torquing the nuts could be the way forward for a stock ish power build?

DEVONMAN · Post by **DEVONMAN** » Sun Sep 25, 2016 3:00 pm

wesbrooks wrote:Thanks. If drilled for cross bolting does it force the need for a line bore?

So studs and not over torquing the nuts could be the way forward for a stock ish power build?

Before you drill and tap for cross bolts you should check for a gap between the side of the caps and the crankcase. The gap will be about 3-4 thou on the starter side of the engine and zero on the other side. If you want to preserve the existing line boring you will need to shim this gap at the point where the cross bolts goes through. Otherwise the cross bolts will pull things out of line and the crank will not rotate freely.

This gap also exists on the factory cross bolted engines but the line boring is done with the cross bolts torqued up and the gap squeezed.

sidecar · Post by **sidecar** » Sun Sep 25, 2016 5:26 pm

chucking some ARP studs in the engine is sounding better all the time!

SimpleSimon · Post by **SimpleSimon** » Sun Sep 25, 2016 8:39 pm

sidecar wrote:chucking some ARP studs in the engine is sounding better all the time!

bigaldart · Post by **bigaldart** » Mon Sep 26, 2016 5:06 pm

The major problem with fretting is that the transfer of metal can result in inconsistent positioning of the mains when removing and refitting. A stud kit alone will not prevent this, we have fretting on our non-crossbolted engines and always use studs at 90 lb/ft torque. One tip from American drag racers who always had the same problem on early type Hemi engines is to ose lanolin on the mating faces of the main caps and block. This acts as a high pressure lubricant so that if the caps move they won't transfer metal from one surface to the other. Lanolin can be bought from some chemists shops or on-line, alternatively some specialist hand creams have 70+% lanolin and can be used in a pinch.

Brutal as it sounds it was a common engineers practice to use a cold chisel to restore the registers. Simply fit and torque the cap, then use a cold chisel on the block web close to the register line and hit with a hammer, A little experimentation on how hard to hit will soon restore the register so that the loose cap fits as snugly as the remainder. With cross bolts you cannot do this so easily.

Alan