SB chevy crankshaft question
Thread Starter
Instructor
Joined: Apr 2005
Posts: 229
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SB chevy crankshaft question
I have a question:
Small block 350
Two piece rear seal block from the 70s
two bolt main
cast crank
Is it possible to swap crankshafts and bearings without puliing the heads, rods and pistons? this is with the engine upside down on a stand out of the car of course.
Small block 350
Two piece rear seal block from the 70s
two bolt main
cast crank
Is it possible to swap crankshafts and bearings without puliing the heads, rods and pistons? this is with the engine upside down on a stand out of the car of course.
Melting Slicks
Joined: Mar 2007
Posts: 2,520
Likes: 11
From: Hinckley OH
I don't see why you couldn't but you would have to remove the damper and timing chain. You would want to take note of the position of the key in the crank so that you don't have to turn it to get the timing marks lined up. You would also have to take care that you don't nick the journals with the studs on the connecting rods when installing it.
Advanced
Joined: May 2013
Posts: 79
Likes: 0
From: Waynesboro PA
That's why I said no. You can do damage to the crank just by letting a rod bolt bump it or scrape it, not to mention your not getting everything clean. You might get lucky and get a few miles out of it.
Race Director
Joined: Dec 1999
Posts: 19,610
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From: Forked River NJ
Yes it is possible to do but probably not the best idea at all. Most likely there will be some damage done. If you have the engine on a stand it will come apart very easily and replace what is needed and do it right.
Advanced
Joined: Apr 2013
Posts: 63
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From: Dawson Springs KY
Back in the late 80's I worked as a mechanic. I've seen it done. I have also seen a perfectly good crank get a ruined by a rod bolt when it was attempted unsuccessfully, it wasn't me that did that, thank God. I would never take the chance but that is my $.02. Yes, it is possible, but, I'll never do it.
A few gaskets and a ring compressor are a lot cheaper than a new crank.
A few gaskets and a ring compressor are a lot cheaper than a new crank.
Last edited by KY_BOB; Jul 23, 2013 at 06:15 PM. Reason: adding
Race Director
Joined: Nov 2006
Posts: 19,445
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From: Athens GA
St. Jude Donor '12-'13, '15- '16-'17-'18-'19, '21
It will take you longer, be messier and possibly not work well with clearances/bearings than if you pulled the engine and turned it over.
I did what you want to do in a marine motor that could not come out of the hold.
Worst 4 days on my back.
Never again.
Bman
I did what you want to do in a marine motor that could not come out of the hold.
Worst 4 days on my back.
Never again.
Bman
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Team Owner
Joined: Jan 2006
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From: Crossville TN
It is possible. You would need to have some soft plastic sleeves for the rod bolts (to cover the threads and protect from damage). And you would need to measure carefully for bearing change-outs...particularly on the rod(s) where the old crank journals are damaged [I'm assuming this is why you want to change it at all].
The other issue is that an engine which has sustained some crank damage might also have sent debris throughout the oil galleries. Hence, why others say that doing this is a BAD idea.
But, you know your situation and the risks involved. So, do what you must.
The other issue is that an engine which has sustained some crank damage might also have sent debris throughout the oil galleries. Hence, why others say that doing this is a BAD idea.
But, you know your situation and the risks involved. So, do what you must.
Thread Starter
Instructor
Joined: Apr 2005
Posts: 229
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crank replace
Motor has been sitting in the back of my shop on stand for years. Was a good rebuilt motor with lots of power but started to get excessive crank endplay. I have an extra crank laying around. That is why I'm asking. I would bet it is already a 30 overbore in cylinders (I didn't do the rebuld) Rebuld lasted 80K miles in truck and it was taking NO oil when pulled and had good oil pressure. No visible metal in oil. Thanks for the replies guys.
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Sure there is...
...the situation the OP presently has. A used engine w/80K miles in decent working condition with a bad crank. The engine is upside down and available to swap the crank out, AND he has a spare crank to put in it. What's so hard to understand about that? He's not trying to rebuild the engine into like-new condition...
...the situation the OP presently has. A used engine w/80K miles in decent working condition with a bad crank. The engine is upside down and available to swap the crank out, AND he has a spare crank to put in it. What's so hard to understand about that? He's not trying to rebuild the engine into like-new condition...
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
I used 3/8" vinyl hose slipped over my con rod bolts to protect the crank. Cheap and very available at any home improvement store.
If I were the op I'd give it a go. Change bearings and put it in.
If I were the op I'd give it a go. Change bearings and put it in.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
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From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Way, way back there I was working in a Chevy dealer- in the truck shop. (Remember when Chevy had BIG Trucks?). One of the guys used to replace the crank in the tall deck 427's and never pull the engine. Did the whole thing from the bottom. HE was kind of a hammer mechanic, but he could swap a complete 427 in a C-70 pretty fast. Then spend 3 days trying to get it to run.
I want the concession for this
, call Earl, Billy Joe and Bubba
We gotta see this.
Race Director
Joined: Nov 2006
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From: Athens GA
St. Jude Donor '12-'13, '15- '16-'17-'18-'19, '21
Way, way back there I was working in a Chevy dealer- in the truck shop. (Remember when Chevy had BIG Trucks?). One of the guys used to replace the crank in the tall deck 427's and never pull the engine. Did the whole thing from the bottom. HE was kind of a hammer mechanic, but he could swap a complete 427 in a C-70 pretty fast. Then spend 3 days trying to get it to run.
Unless there is some real problem with pulling the engine such as no crane/lift/hoist why make it so hard on yourself.
While you have it out and upside down you can check a lot more carefully and not risk damage to parts with critical finishes (journals, etc.). If it is a 2pc rear main seal and you don't get it right you will have another problem to deal with next week.
I realize circumstances are not always in our control.
I did rod bearings on a 1974 Honda civic laying on a tarp in snow from under the car but only cause I had to. It was in my gf driveway in 1980.
Good luck with whatever you choose.
Bman
Le Mans Master
Joined: Apr 2011
Posts: 6,284
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From: Hermosa
I realize circumstances are not always in our control.
I did rod bearings on a 1974 Honda civic laying on a tarp in snow from under the car but only cause I had to. It was in my gf driveway in 1980.
I did rod bearings on a 1974 Honda civic laying on a tarp in snow from under the car but only cause I had to. It was in my gf driveway in 1980.
I remember changing a head gasket on a 84 Buick behind an apartment complex in the weeds. I ended up putting in two head gaskets (they were cheap back then) because the head was warped and I did not have the time or money to get it planed flat. Did the who job without a torque wrench and one cheap made in Taiwan tool set. It didn't care, it ran fine until I sold it 1 1/2 years later.
Safety Car
Joined: Mar 2007
Posts: 3,652
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From: Bridgewater nj
I've done it but my bearings were just barely knocking at low idle and a very hot engine.
My advise.
Loosen all the mains.
Pull the crank and rods down a little bit
Then tap out each main and replace.
Then do each rod one at a time.
If you come across a bad journal, scrape the whole project and pull the motor.
If I had to do it again, I would of pulled the motor and purchased a simple rering kit from summit.
My advise.
Loosen all the mains.
Pull the crank and rods down a little bit
Then tap out each main and replace.
Then do each rod one at a time.
If you come across a bad journal, scrape the whole project and pull the motor.
If I had to do it again, I would of pulled the motor and purchased a simple rering kit from summit.
Last edited by hugie82; Jul 25, 2013 at 11:46 AM.