Engine Rebuild Question
Thread Starter
Cruising
Joined: Feb 2006
Posts: 10
Likes: 0
From: Oviedo Florida
Engine Rebuild Question
I'm rebuilding a 67 - 327 and have a question regarding the main bearing caps for the crank. I've had the engine apart for awhile and don't remember the location of the caps - which cap went where. Does it make a difference??? All the caps have some raised markings but it's not obvious to me that these marking define the cap location. Here are the markings:
Cap 1) an arrow (which I assume means locate arrow facing towards front of engine), a F turned side ways and the following numbers 7178. Underneath this line of info is GM 3
Cap 2) Same as cap one but has GM 4 N
Cap 3) Same as cap one but has GM 14 N
Cap 4) Same as cap one but has GM 26 N or it could be 28 N (not sure if it is a 6 or 8)
Visually looking at the caps I can see no difference and can not find any other markings. What do you think????
Cap 1) an arrow (which I assume means locate arrow facing towards front of engine), a F turned side ways and the following numbers 7178. Underneath this line of info is GM 3
Cap 2) Same as cap one but has GM 4 N
Cap 3) Same as cap one but has GM 14 N
Cap 4) Same as cap one but has GM 26 N or it could be 28 N (not sure if it is a 6 or 8)
Visually looking at the caps I can see no difference and can not find any other markings. What do you think????
Melting Slicks
Joined: Sep 2004
Posts: 2,917
Likes: 13
From: NE Illinois IL
well, aside from the last cap, they are all interchangable. That said, the line bore by GM or your machine shop was done with the caps in a specific order.
If you can't figure out how you had it, try installing the bearings and crank and checking clearances and crank spin. If you are off on any, you may get some clues (i.e. #1 has a big clearance, #2 a small then switch them and repeat).
If you can't figure out how you had it, try installing the bearings and crank and checking clearances and crank spin. If you are off on any, you may get some clues (i.e. #1 has a big clearance, #2 a small then switch them and repeat).
Race Director
Joined: Nov 2000
Posts: 10,340
Likes: 664
From: Beverly Hills (Pine Ridge) Florida
Normally an engine rebuilder would mark the caps with either punch marks (1 "dit" for #1, 2 "dits" for #2, etc., etc.), or would of used numbered punches to indicate which cap is which. This would of been done prior to the cap removal.
I assume you did the initial tear down, and did not do the above.
As Joel 67 stated, if no markings, then you are playing a guessing game with trial and careful measurements.
Have to ask: Were the rod caps numbered and/or kept with their respective rods?
Plasticman
I assume you did the initial tear down, and did not do the above.
As Joel 67 stated, if no markings, then you are playing a guessing game with trial and careful measurements.
Have to ask: Were the rod caps numbered and/or kept with their respective rods?
Plasticman
Race Director
Joined: Feb 2004
Posts: 14,984
Likes: 185
From: CT
Don't second guess, or go by trial & error. If you aren't positive which cap goes to which bearing you will need to have it align bored. It makes little to no sense to get it all together and then find out it screwed up.
Instructor
Joined: May 2006
Posts: 211
Likes: 0
From: N. Tustin Ca
well, aside from the last cap, they are all interchangeable. That said, the line bore by GM or your machine shop was done with the caps in a specific order.
If you can't figure out how you had it, try installing the bearings and crank and checking clearances and crank spin. If you are off on any, you may get some clues (i.e. #1 has a big clearance, #2 a small then switch them and repeat).
If you can't figure out how you had it, try installing the bearings and crank and checking clearances and crank spin. If you are off on any, you may get some clues (i.e. #1 has a big clearance, #2 a small then switch them and repeat).
I agree with Joel, you'll have to fit and mic them. Here's what I've done, Get 8 large numbered coffee cans fill with oil and keep partsfrom each cylinder separate, pistons, rods, caps, lifters, push rods, and
pins, bearings etc. You wont have to sit and watch rust until you get time to put all back together
Burning Brakes
Joined: Aug 2001
Posts: 1,104
Likes: 1
From: Frederick Md
Wow!
I'm rebuilding a 67 - 327 and have a question regarding the main bearing caps for the crank. I've had the engine apart for awhile and don't remember the location of the caps - which cap went where. Does it make a difference??? All the caps have some raised markings but it's not obvious to me that these marking define the cap location. Here are the markings:
Cap 1) an arrow (which I assume means locate arrow facing towards front of engine), a F turned side ways and the following numbers 7178. Underneath this line of info is GM 3
Cap 2) Same as cap one but has GM 4 N
Cap 3) Same as cap one but has GM 14 N
Cap 4) Same as cap one but has GM 26 N or it could be 28 N (not sure if it is a 6 or 8)
Visually looking at the caps I can see no difference and can not find any other markings. What do you think????
Cap 1) an arrow (which I assume means locate arrow facing towards front of engine), a F turned side ways and the following numbers 7178. Underneath this line of info is GM 3
Cap 2) Same as cap one but has GM 4 N
Cap 3) Same as cap one but has GM 14 N
Cap 4) Same as cap one but has GM 26 N or it could be 28 N (not sure if it is a 6 or 8)
Visually looking at the caps I can see no difference and can not find any other markings. What do you think????
Race Director
Joined: Feb 2007
Posts: 15,424
Likes: 8,873
From: northern california
C2 of Year Finalist (track prepared) 2019
An anecdote that may help you decide what to do:
Friend of mine had an engine built for his '58 vintage racer. After the engine was dynoed (394 HP out of a 283), his engine builder decided it would be a good idea to put in fresh bearings.
Back together and in the car, the engine lasted only a handful of laps before it began losing power. In short order the engine seized, locking the rear wheels and sending my buddy into a spin.
The post mortem showed that two or more of the bearing caps had been swapped around when the bearings were replaced after the dyno pulls.
Draw your own conclusions......
Jim
Friend of mine had an engine built for his '58 vintage racer. After the engine was dynoed (394 HP out of a 283), his engine builder decided it would be a good idea to put in fresh bearings.
Back together and in the car, the engine lasted only a handful of laps before it began losing power. In short order the engine seized, locking the rear wheels and sending my buddy into a spin.
The post mortem showed that two or more of the bearing caps had been swapped around when the bearings were replaced after the dyno pulls.
Draw your own conclusions......
Jim
Race Director
Joined: Feb 2004
Posts: 11,032
Likes: 2,587
From: Del Boca Vista FL
If you have mixed up the four forward caps an align bore or align hone is in your future prior to reassembly of the motor. I do not recommend playing guessing games with your main bearings. The align bore/align hone makes sure you are bedding the bearings and crankshaft correctly.
OR you can guess at the proper positions of the four main bearing caps and, if you are wrong, you can then spend additional money having the crankshaft reground, purchasing new bearings, purchasing another gasket set, possibly having the rods reconditioned and then have block align bored after you ruin it.
Your Call.
If you are building a performance motor have a machine shop install the splayed caps on the three center caps prior to align bore. You won't regret it. Strengthens the main webbing.
Rich
OR you can guess at the proper positions of the four main bearing caps and, if you are wrong, you can then spend additional money having the crankshaft reground, purchasing new bearings, purchasing another gasket set, possibly having the rods reconditioned and then have block align bored after you ruin it.
Your Call.
If you are building a performance motor have a machine shop install the splayed caps on the three center caps prior to align bore. You won't regret it. Strengthens the main webbing.
Rich
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Burning Brakes
Joined: Aug 2001
Posts: 1,104
Likes: 1
From: Frederick Md
If you have mixed up the four forward caps an align bore or align hone is in your future prior to reassembly of the motor. I do not recommend playing guessing games with your main bearings. The align bore/align hone makes sure you are bedding the bearings and crankshaft correctly.
OR you can guess at the proper positions of the four main bearing caps and, if you are wrong, you can then spend additional money having the crankshaft reground, purchasing new bearings, purchasing another gasket set, possibly having the rods reconditioned and then have block align bored after you ruin it.
Your Call.
If you are building a performance motor have a machine shop install the splayed caps on the three center caps prior to align bore. You won't regret it. Strengthens the main webbing.
Rich
OR you can guess at the proper positions of the four main bearing caps and, if you are wrong, you can then spend additional money having the crankshaft reground, purchasing new bearings, purchasing another gasket set, possibly having the rods reconditioned and then have block align bored after you ruin it.
Your Call.
If you are building a performance motor have a machine shop install the splayed caps on the three center caps prior to align bore. You won't regret it. Strengthens the main webbing.
Rich
Let's clear up a couple of things, if you need to align bore a block you are in deep dodo, most passenger car blocks are align HONED, not BORED then honed. Align Boring removes more material than you want to deal with.
As far as matching up the caps with the saddles using the pattern left bt the original hone, been there done that because dumb *** want a be engine builders did not stamp the caps and decided to pay to have the problem corrected.
Unless a block needs align honing then I don't do it and a little time spent here by a good machist can salvage this man made problem.