crankshaft breaks
Thread Starter
Heel & Toe
Joined: Mar 2010
Posts: 19
Likes: 0
crankshaft breaks
Took my 87 C4 to a shop this week to have engine rebuilt because of
a knock in the lower end I was told it could be a crankshaft which is cast
that GM had problems with in this year. I'm asking for input on this
because I've really never heard of a crank breaking in half. My oil pressure
was 40-60 psi. and the engine would idle but had a scrapping noise along
with a deep knock and binging while aplying fuel.
a knock in the lower end I was told it could be a crankshaft which is cast
that GM had problems with in this year. I'm asking for input on this
because I've really never heard of a crank breaking in half. My oil pressure
was 40-60 psi. and the engine would idle but had a scrapping noise along
with a deep knock and binging while aplying fuel.
Le Mans Master
Joined: Nov 2009
Posts: 6,882
Likes: 234
From: Bangkok, Thailand
In my 30 years of being a car guy I've only seen one crank physically break in a friends car.
Much more likely that you've developed rod knock. If that's the case, you need either a complete rebuild (no point in doing it half way) or buy a crate engine.
If you go the crate engine route, don't overlook the HT 383. You can get just the bottom end for a good price considering it's an all new engine with 1 piece rear seal and hydrualic rollers. The cam is small, but it still makes great power - about 100 hp more than your stock engine. Just get your heads rebuilt and install them on that block. You could go for a bigger cam easily at that point oo if you want to, or just keep the mellow cam and enjoy the smooth driveability.
Much more likely that you've developed rod knock. If that's the case, you need either a complete rebuild (no point in doing it half way) or buy a crate engine.
If you go the crate engine route, don't overlook the HT 383. You can get just the bottom end for a good price considering it's an all new engine with 1 piece rear seal and hydrualic rollers. The cam is small, but it still makes great power - about 100 hp more than your stock engine. Just get your heads rebuilt and install them on that block. You could go for a bigger cam easily at that point oo if you want to, or just keep the mellow cam and enjoy the smooth driveability.
Melting Slicks
Joined: Mar 2002
Posts: 3,108
Likes: 126
From: S.L.C. UT
Cranks do break I have seen it happen several times. And it still can run with a broken crank. Alot of times the crank breaks at a angle, and it will still run. Probably not very good or smooth, but it will still run. It's not real common to see a crank break though.
When I used to wrench for a living, I had a late 80's 1 ton Chevy truck that the damper/pully was wobbling. Started it up and drove it in and it broke the crank just behind #1 main cap.And it really didn't make that much noise. And I had another one break right in the middle, and it ruined the block, but I drove it into the shop. It seems like it's more common with big trucks that haul alot of weight. But it can happen in our cars. A bad damper can also cause it if it's not properly controlling harmonics.
When I used to wrench for a living, I had a late 80's 1 ton Chevy truck that the damper/pully was wobbling. Started it up and drove it in and it broke the crank just behind #1 main cap.And it really didn't make that much noise. And I had another one break right in the middle, and it ruined the block, but I drove it into the shop. It seems like it's more common with big trucks that haul alot of weight. But it can happen in our cars. A bad damper can also cause it if it's not properly controlling harmonics.
Last edited by tpi 421 vette; Jun 17, 2010 at 12:04 AM.
Burning Brakes
Joined: Feb 2010
Posts: 1,013
Likes: 2
From: California City Ca
Sorry about hijacking But
I notice your from CA I have been looking to go through my motor or crate motor if I put a 383 kit in my 86 l98 motor.
With the stock iron heads and intake a little hotter cam will I pass CA smog.
I would like to run a set of headers but the precats kill that idea.
With the stock iron heads and intake a little hotter cam will I pass CA smog.
I would like to run a set of headers but the precats kill that idea.
In my 30 years of being a car guy I've only seen one crank physically break in a friends car.
Much more likely that you've developed rod knock. If that's the case, you need either a complete rebuild (no point in doing it half way) or buy a crate engine.
If you go the crate engine route, don't overlook the HT 383. You can get just the bottom end for a good price considering it's an all new engine with 1 piece rear seal and hydrualic rollers. The cam is small, but it still makes great power - about 100 hp more than your stock engine. Just get your heads rebuilt and install them on that block. You could go for a bigger cam easily at that point oo if you want to, or just keep the mellow cam and enjoy the smooth driveability.
Much more likely that you've developed rod knock. If that's the case, you need either a complete rebuild (no point in doing it half way) or buy a crate engine.
If you go the crate engine route, don't overlook the HT 383. You can get just the bottom end for a good price considering it's an all new engine with 1 piece rear seal and hydrualic rollers. The cam is small, but it still makes great power - about 100 hp more than your stock engine. Just get your heads rebuilt and install them on that block. You could go for a bigger cam easily at that point oo if you want to, or just keep the mellow cam and enjoy the smooth driveability.
Le Mans Master
Joined: Nov 2009
Posts: 6,882
Likes: 234
From: Bangkok, Thailand
There is a thread here about re-drilling the Vortec heads (you'll need to register to view it) http://www.crossfire.homeip.net/inde...showtopic=2220
BTW, there are no CA legal headers for 84-91 Corvettes - at least not that I've found yet.
One more CA consideration - the EGR system. The vortech heads don't have an EGR crossover, but you could use a passenger side header from a later (aluminum head) car to get the EGR fed that way. I'm not sure of the year cut-offs for that stuff, so you'd have to do a little digging there.
Last edited by mcm95403; Jun 17, 2010 at 03:09 AM.
Cruising
Joined: Oct 2009
Posts: 10
Likes: 0
I've had 2 cranks break on me. 86 Grand National and 96 Olds 88. Both 3.8 liter v-6. An engine will not turn with a broken crank. We put a 4 ft. cheater bar on my GN's Harmonic balancer and it wouldn't budge. Olds was locked up tight too. Definitely get a second opinion. I had a 4Runner that was making the same sounds as yours. Ended up being a thrust bearing had fallen out. It was letting the crank slide back and forth, hitting the block when accelerating.
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Le Mans Master
Joined: Nov 2009
Posts: 6,882
Likes: 234
From: Bangkok, Thailand
One correction to the post above - apparently the short block does NOT include a cam and lifters, so for $900 more you get the complete valvetrain, Vortec heads and an intake manifold you can sell off to recoup some cash.
Also, check out this online dyno setup: http://www.gmperformanceparts.com/en...no.jsp?eng=383
It lets you custom build the engine from certain parts to see what it will do. The torque output of the engine as-is is awesome - total stump puller! Teamed with some (numerically) low gears, you'd have a really flexible setup.
Check out this PDF dyno run from that site. It's the dead stock HT 383 engine with 1.6 roller rockers and a single plane intake: http://www.marcmedina.com/temp1/crat...ood_intake.pdf
377 ft/lbs of torque at 1500 rpm (more than 400 between 1700 thru 4600) with a peak hp output of 354 by 4700 rpm - it's like driving a mild big block. No need to rev the snot out of it, just hit the throttle and hang on!
Also, check out this online dyno setup: http://www.gmperformanceparts.com/en...no.jsp?eng=383
It lets you custom build the engine from certain parts to see what it will do. The torque output of the engine as-is is awesome - total stump puller! Teamed with some (numerically) low gears, you'd have a really flexible setup.
Check out this PDF dyno run from that site. It's the dead stock HT 383 engine with 1.6 roller rockers and a single plane intake: http://www.marcmedina.com/temp1/crat...ood_intake.pdf
377 ft/lbs of torque at 1500 rpm (more than 400 between 1700 thru 4600) with a peak hp output of 354 by 4700 rpm - it's like driving a mild big block. No need to rev the snot out of it, just hit the throttle and hang on!
Last edited by mcm95403; Jun 17, 2010 at 01:52 AM.
Melting Slicks
Joined: Mar 2002
Posts: 3,108
Likes: 126
From: S.L.C. UT
I've had 2 cranks break on me. 86 Grand National and 96 Olds 88. Both 3.8 liter v-6. An engine will not turn with a broken crank. We put a 4 ft. cheater bar on my GN's Harmonic balancer and it wouldn't budge. Olds was locked up tight too. Definitely get a second opinion. I had a 4Runner that was making the same sounds as yours. Ended up being a thrust bearing had fallen out. It was letting the crank slide back and forth, hitting the block when accelerating.
Last edited by tpi 421 vette; Jun 17, 2010 at 02:22 AM.
Le Mans Master
Joined: Nov 2009
Posts: 6,882
Likes: 234
From: Bangkok, Thailand
I think it depends where the crank breaks, and what angle the break is. I have also seen a engine lock up with a broken crank, or worse cause a major explosion. But I have also seen and drove engines with broken cranks as mentioned. I am not making this stuff up. I was a ASE Certified Master Auto Technician, not a lube boy.
It takes a lot to break a crank.
Thread Starter
Heel & Toe
Joined: Mar 2010
Posts: 19
Likes: 0
crankshaft break
Thanks to everyone that replied to my problem I'll keep you posted
on the problem, motor is out now and should have oil pan off to check
sometime tomorrow. If it is a crankshaft break should the block be line
bored? I'm being told it should by the shop which is another $175.00 on
top of the quote now I think I'm being nickel and dimed just so they
can make more. I'm really at there mercy now.
on the problem, motor is out now and should have oil pan off to check
sometime tomorrow. If it is a crankshaft break should the block be line
bored? I'm being told it should by the shop which is another $175.00 on
top of the quote now I think I'm being nickel and dimed just so they
can make more. I'm really at there mercy now.
Le Mans Master
Joined: Nov 2009
Posts: 6,882
Likes: 234
From: Bangkok, Thailand
Former Vendor
Joined: Nov 2006
Posts: 2,482
Likes: 3
From: Carmichael ca
On the "broken" crank. 87s did not have a problem with their cranks. In 28 years as a mechanic, I too have seen broken cranks, but they are rare and usually very loud.
Thread Starter
Heel & Toe
Joined: Mar 2010
Posts: 19
Likes: 0
Just got the word from the shop knocking noise was #1 rod bearing and the rod has
damaged the crank to where they will need to weld and turn or used crank I'm go with
a new crank everything else block, heads, intake good, will bore and have
flat top pistons, cam, springs, valves etc. put in also..
damaged the crank to where they will need to weld and turn or used crank I'm go with
a new crank everything else block, heads, intake good, will bore and have
flat top pistons, cam, springs, valves etc. put in also..