Main cap walking/fretting on stock tune.

Mickey427 · Jun 24, 2015

I have a 95 7.3 that I had to pull the motor out due to a cracked timing cover. While I had it out I decided to do a little turbo work and build a windage tray for it. While everything was apart I figured it'd be good to pull a few caps off and check bearings. I have about 30k on this rebuild where I installed arp main studs to cure the cap walk problem I thought I had from my edge evolution programmer. Truck currently has a set of beans stage 1s from ddp and his D66 turbo. Stock tuning on this rebuild since I didn't have the spare coin for a chip and it was nice not having it break down lol. My question is how can I have a main cap walking problem with arp studs and a stock tune? The rod bearings look practically brand new but the mains look as if the cap somehow got twisted in the registers a bit causing kiddy corner wear marks. I did the align hone myself on a sunnen align hone set to the lower side of the tolerance. Hopefully my pics show up. Thanx for the help!

gwunter · Jun 24, 2015

I probably don't have your answer, but did you plasti-gauge these before final assembly??

Mickey427 · Jun 24, 2015

No plasti-gauge. Used a sunnen tenth reading dial bore gauge and had .0035 clearance, give or take a tenth.

Isobaric · Jun 24, 2015

Mickey427 said:
No plasti-gauge. Used a sunnen tenth reading dial bore gauge and had .0035 clearance, give or take a tenth.

A tenth? I hope you are mistaken on your units....

Dmstrucks02 · Jun 24, 2015

Isobaric said:
A tenth? I hope you are mistaken on your units....

I thought the same thing

Sent from my SAMSUNG-SGH-I537 using Tapatalk

Mickey427 · Jun 24, 2015

Sorry, that's machinist slang. To a engine machinist a tenth is .0001 they will always say one hundred thousandth for .100

Magnum PD · Jun 24, 2015

The ARP studs won't eliminate crank walk. Block fill first then maybe a girdle or bedplate to fully take care of that.

Mickey427 · Jun 24, 2015

I don't have a 600hp truck, I have a set of stage 1s injectors which behave just like stock injectors when running stock tuning and a D66 turbo. In all reality I MAYBE have 20-30 more hp than a bone stock pickup. My question isn't how to eliminate cap walk but why is it a problem for me with basically a stock HP engine?

Magnum PD · Jun 24, 2015

Still have block flex under heavy towing.

NyCowboy87 · Jun 25, 2015

If you didn't machine the cap seats and block to cap surfaces that already had fretting how do you expect it to not move around? You have two uneven mating surfaces, big deal if you put studs in it and honed it.

Sent from my iPhone using Tapatalk

Mickey427 · Jun 25, 2015

Obviously filing the block and trimming the main caps is part of the align hone process, if you tried to hone the mains on a block straight you would be way bigger than the main bore max diameter spec and loose all bearing crush causing an immediate spun bearing.

NyCowboy87 · Jun 25, 2015

Alright my apologies, didn't see anywhere above that it was done. Can't assume anything, I've seen some pretty shady stuff from shops.

Sent from my iPhone using Tapatalk

m j · Jun 28, 2015

any pics of the block side of this?

drunk on diesel · Jun 28, 2015

Magnum PD said:
Still have block flex under heavy towing.

so you can't tow heavy with a 7.3 with small aftermarket injectors or the block will flex?

nossliw · Jun 29, 2015

drunk on diesel said:
so you can't tow heavy with a 7.3 with small aftermarket injectors or the block will flex?

120k later and my caps look nothing like that....

drunk on diesel · Jun 29, 2015

they probably won't look like that 320k later

Magnum PD · Jun 29, 2015

Mine looked very similar to them. Not every engine is the same.

elrodalexander73 · Jun 29, 2015

I would be looking very carefully at the surface where the main meets the block on the sides of the mains, as the block flexes the material is comprised all but very little and over enough time the caps move in a kind of a criss cross movement. I remember when Cummins upped the H.P on N14s and had this problem, we used to use green Loctite, NO CHIT and Loctite the main bearing caps into the block and use blue on the bolts with ample amounts of oil to torque them properly, this was an ACTUAL service bulletin from Cummins engineering dept.. This prevented some possibility of walk and worked on several engines with less than severe fretting. I prefer plasti gauging in several different places on the crank as well to see how absolutely perfect the journal on the crank it self is, how many miles was on the block before you machined it and what type of life did it exhibit is another factor.. I remember N14s in Over the road trucks were hardly ever worn badly when rods and mains went in, but on the Michigan specials we Loctite'd every cap carefully due the operational load impeded on the engines.

golfer · Jun 30, 2015

drunk on diesel said:
so you can't tow heavy with a 7.3 with small aftermarket injectors or the block will flex?

..depends on the block.

were your block bores measured with & without a torque plate installed to see what kind of flex your block has?

we see quite a big difference from 'a' block to 'another' block...

the super flexy ones go to scrap...the acceptable ones are used for stock-ish power rebuilds...and the rigid blocks are used for high hp builds.

(I believe the OP & I spoke on the phone late last week?)...but in his case, aside from the fretting, his uneven bearing wear is most likely from the main journals being line honed, not line bored...and his caps being twisted on the main journals.

We have a right angle gear drive attachment for our Rottler F69ATC which is the only method we've found to successfully and repeatedly correct factory misaligned main caps/skewed/twisted caps.

elrodalexander73 · Jun 30, 2015

I know this is off subject, but this is a question for Golfer, which blocks are the better ones too use, I know there is serial # break where they added more material around the lifter gallery bores, but which ones have you guys seen that have more flaws than other blocks. Are there a series of serial #s to avoid??