OK, so I need to know how bad this is - broken crankcase cap

[ChinStokes]

So I was torquing down the caps, and although I had tapped them all into place before starting, one came out of the recess it needs to be in and I didn't notice until, you guessed it, the part of the cap outside the bolt snapped.

Am I totally hosed here or is there some way to make this work?

Thanks in advance.
Christian

 

[dla4567]

Crankshaft bearing cap?
A picture would help.

 

[furyus]

I wouldn't use a cracked crankshaft cap for any reason. Locate a new cap. You might have to have the block line bored with a new cap. Smarter guys on here will hopefully chime in.

 

[PurpleBeeper]

OK, good news....you didn't get the motor in the car & have it throw a rod after 5 miles, so count your blessings.

It's a pain, but if this is a performance motor, then you need to take it back apart & re-align hone the main journals after getting a new cap. For a cruiser stock-type motor, you might get away with putting in another cap. WHAT DO YOU GUYS THINK?

 

[JB400]

If it's a rod cap, you can get by with it, unless it's a performance motor, then it needs to be rebalanced.

If it' a main cap, then I'd consider replacing them all, and have it align honed as mentioned earlier.

 

[66383]

Do it right …..Now or it'll be later and you won't be doing this...

 

[Cranky]

You will be a lucky dog if you can find a main cap that will bolt in without the need for machining......but even with it not fitting, I don't see any reason to replace the others. You might get lucky.....I've seen stranger things happen. If you find one that looks good, mic it but you need to know how to use em to make sure it actually does fit right.

 

[bm02tj]

With a new main cap I would go line bore as you do not take any of the block just the cap
Strip it and see your local machinist
You may need to take to industrial shop for line bore as most auto shops just have line hone

 

[Kern Dog]

From what I read, the one that cracked did so because the surface of the main cap was not properly seated.
Many here suggested a line hone after replacing the cap. In theory, I agree. I wonder though what would happen if you tried a different main cap then checked clearance with Plastigage...? If it is within tolerances and the crank spins freely, you may be okay to run it as is.

 

[Cranky]

You may need to take to industrial shop for line bore as most auto shops just have line hone

What? The auto shops around here have the proper machinery to do the job right...and to check if things are in alignment and round. Do you know why most shops recommend align boring etc? Because they don't want to spend the time checking things first! They just rather throw it up on the table and cut cut cut. They don't want to take the time to check it and it makes them money. You bet your sweet butt that you had better be able to check their work once they are done though because most do NOT check their own machine work. The last block I got back from the shop after it was aligned bored and honed was out of round .003"!!!! Dumb asses. Took it back and told them to please do it right thank you. Wasted my time and that pisses me off. And this shop built Pro Stock engines.....geeez.

 

[wyrmrider]

new cap and line bore no other way I know
swapping caps has been tried but I've never seen it work
I've had to fix several of these DIY fixes- not pretty
screw the line hone, you are going to cut the parting face of the new cap and cut a new round hole in the cap only
with luck you will not touch the bloc
if you do you have to do all 5

 

[bm02tj]

95% of the time line hone is ok but you need to bore so not to damage block
Where I live the auto machine shop only have line hone and sub out if it needs boring
as in gear drive cams or new caps

 

[happyjackdaddy54]

With a new main cap I would go line bore as you do not take any of the block just the cap
Strip it and see your local machinist
You may need to take to industrial shop for line bore as most auto shops just have line hone

IF they have a line hone, have that done! It takes off metal than a line bore. Only line bore as a last resort If you want to fix it right replace ALL caps. Price will be the same!

 

[wyrmrider]

I can take a tenth off from where I want to take it off with a line bore
line hones usually work on upside down block so even gravity helps them take more off the block than the caps, even on the journals that need nothing removed
now what do you do with all your journals oval shaped?
Bring em in and I'll fix em (or would have before I retired)
also once you start you have to watch your cam chain and figure when you have to go to a shorter chain and bore to that dimension

 

[493 Mike]

I would spend the money and buy new heavy duty main caps and studs. Thus you will have beefed the bottom end for now or the future and made the block more valuable too. It probably costs the same to set up the machine for one or five bores.
As for line boring verses line honing: the line bore cutter can be set to just barely cut the block, removing the majority of iron from the caps thus keeping the timing chain tight or negating the need to buy a special, shorter timing chain.
Mike

 

[Cranky]

IF they have a line hone, have that done! It takes off metal than a line bore. Only line bore as a last resort If you want to fix it right replace ALL caps. Price will be the same!

I don't get the reasoning on replacing all caps. They are all going to be face cut then reinstalled and then aligned be it with a cut or a hone however, I like finding caps that are as close as possible for the machining operation. Personally, I like em honed. Been a machinist for a long time and know what I'm talking about.....

 

[JB400]

The purpose of replacing all the caps is fatigue. If you break one, what's to say others won't go as well? Replacing all the caps and adding new studs is just insurance.

 

[Cranky]

The purpose of replacing all the caps is fatigue. If you break one, what's to say others won't go as well? Replacing all the caps and adding new studs is just insurance.

I understand doing that in a high horse build but the OP broke a cap because it wasn't seated and he torqued it down snapping it. If his caps are fatigued, what's the rest of the block like?

 

[JB400]

He just needs to start from square one, and have everything sonic checked, then make decisions.

 

[wyrmrider]

Everyone would like new steel or aluminum or hd whatever caps
economics dictate a stock replacement cap on low performance engines
I would do studs if I was going to replace a cap and line bore
bottom tap, hard washers the whole 9 yards
but remember studs help most when the engine is going to be torn down on a regular basis
and the fine threads give better torque/ clamp control
if your are putting it together once for the long haul bolts work fine
example sorta (Studs We don't need no stinking studs)
on our Rambler 199 +.010 for 210 cu in we ground the tops of the caps flat and installed steel straps using stock half inch head bolts for the mains
over 1,200 hp on several pulls and over 1000 for 30 minuets never any crank problems with either stock high psi nodular iron or aramasteel cranks
60 lbs boost twin turbos, methanol, rich
on a BBM the girdles do help but you can break anything, also a short fill b4 the line bore