Damn Crank!

[Dreamcar86]

Last week I posted a thread thinking my cam sensor interrupter ring broke causing a nasty backfire. After pulling the engine it looks like the crank gave creating the problem.
Anyone know where the best place to find a block would be? Also what crank would you use moving forward?

Check out the crank, block, rod and piston.

 

[Dreamcar86]

Few more pics.

 

[jasjamz]

I can tell you from experience you will want to have your builder find it if he is out of state. I shipped one that was no good due to a hairline crack in the main web. $200 wasted. He got me one from Grumpy. I am about to go out and put it to use right now...

 

[TurboBuRick]

Holy smokes!

 

[Boost231]

sorry to see this,

what kind of #'s where you running in the 1/4?

 

[Dreamcar86]

sorry to see this,

what kind of #'s where you running in the 1/4?

Funny you should ask. At 18lbs of boost 11.30's. I was going to shoot for high 10's this season however it will not happen with that engine obviously. Looks like we'll have to build a stronger one that will.:biggrin:

 

[Dreamcar86]

I can tell you from experience you will want to have your builder find it if he is out of state. I shipped one that was no good due to a hairline crack in the main web. $200 wasted. He got me one from Grumpy. I am about to go out and put it to use right now...

Good advice. That would only upset matters worse to buy and unusable block. I have really thought about heading to the salvage yard to see if there are any 3.8 blocks that are usable.

 

[2QUICK2B6]

18#'s built engine hmmm

 

[Dreamcar86]

18#'s built engine hmmm

Not sure what that means but that was the original stock crank. That was stupid on my part to have rebuilt it with a stock crank and now I paid the price. 24 year old parts will give.

 

[2QUICK2B6]

The stock crank can and has taken alot of abuse ... i would think u had serious knock. jmo ... I rebuilt an engine with a stock crank looking to go low 10's

 

[Dreamcar86]

The stock crank can and has taken alot of abuse ... i would think u had serious knock. jmo ... I rebuilt an engine with a stock crank looking to go low 10's

That was not a race related break, I was getting onto the highway on an acceleration lane. Not sure till I tear it down what caused the problem. Initially I thought it jumped time due to a broken interrupter ring on the cam sensor now I am thinking differently. Need to look at the bearings and see if there was a problem there.

 

[jasjamz]

Yeah, I took my engine out running and it had a studded 109, stock crank, TRW pistons, caps on 1,2, and 3, like you. It was onlny a matter of time before that crack caused a major issue. I did have 5 bent stock rods too. I had a cam sensor failure in that engine the previous year.

 

[Boost231]

makes me wonder. i guess its all in luck. i have about the same build, 109, .30 cp pistons, 212/212, 2 billet caps, arp's throughout, etc stock crank, stock rods. i guess time will tell. 11.00's right now at 23psi

 

[TurboDave]

That was not a race related break, I was getting onto the highway on an acceleration lane. Not sure till I tear it down what caused the problem. Initially I thought it jumped time due to a broken interrupter ring on the cam sensor now I am thinking differently. Need to look at the bearings and see if there was a problem there.

Cam sensor doesn't have anything to do with timing. Just sets up the injector firing sequence. Wonder what could have caused the crank to break so badly. It should have been able to take what you were throwing at it. Unless it had a crack and just kept getting worse over time. Did you mag it before re-installing it?

 

[qwknuf6 jr]

Cam sensor doesn't have anything to do with timing. Just sets up the injector firing sequence. Wonder what could have caused the crank to break so badly. It should have been able to take what you were throwing at it. Unless it had a crack and just kept getting worse over time. Did you mag it before re-installing it?

A broken cam sensor ring will throw timing off , as it rotates out of postion it will cause a major backfire . Common issue with a roller cam motor. Not sure that is what cause the damage , will need to look at all the damage after full teardown.

Mark

 

[TurboDave]

A broken cam sensor ring will throw timing off , as it rotates out of postion it will cause a major backfire . Common issue with a roller cam motor. Not sure that is what cause the damage , will need to look at all the damage after full teardown.

Mark

Not saying it wont cause a major backfire(from fuel puddling) but.... Crank sensor controls ignition timing. Cam sensor merely syncs the injectors to the crank reference.

 

[ijames]

Not saying it wont cause a major backfire(from fuel puddling) but.... Crank sensor controls ignition timing. Cam sensor merely syncs the injectors to the crank reference.

I know this is a little picky, but you are correct but don't go quite far enough. If the cam sensor moves enough so that the crank sensor sync jumps to the next window the timing will jump 120 degrees which will cause everything from a miss to a backfire, and technically this is a timing error caused by the cam sensor . I have seen one engine in my life where the timing chain would stretch just enough to cause this every now and then. Took a long time to find because everything always looked good engine off, idling, or even revved up sitting still. Go for a drive and under a load it would miss and pop. Finally got just bad enough we could get it to pop making a little boost against the footbrake, and then the timing light clearly showed the jump. We just moved the cam sensor a little farther over and problem solved.

 

[qwknuf6 jr]

Not saying it wont cause a major backfire(from fuel puddling) but.... Crank sensor controls ignition timing. Cam sensor merely syncs the injectors to the crank reference.

WRONG

backfire is not from fuel puddling , it is an ignition backfire , I will let you draw your own conclusions as to why the engine backfires when the cam sensor ring breaks and moves inside the cap

Mark

 

[qwknuf6 jr]

I know this is a little picky, but you are correct but don't go quite far enough. If the cam sensor moves enough so that the crank sensor sync jumps to the next window the timing will jump 120 degrees which will cause everything from a miss to a backfire, and technically this is a timing error caused by the cam sensor . I have seen one engine in my life where the timing chain would stretch just enough to cause this every now and then. Took a long time to find because everything always looked good engine off, idling, or even revved up sitting still. Go for a drive and under a load it would miss and pop. Finally got just bad enough we could get it to pop making a little boost against the footbrake, and then the timing light clearly showed the jump. We just moved the cam sensor a little farther over and problem solved.

You are on the right trail , how would the crank sensor know when to start ignition sequence with just three windows .....hmmmmm

Mark

 

[Blazer406]

You are on the right trail , how would the crank sensor know when to start ignition sequence with just three windows .....hmmmmm

Mark

Once the engine is running..... it will stay running fine..... even with the cam sensor unplugged. As previously stated....cam sensor doesn't directly effect the ignition timing.....unless you are far enough off like Carl says......


dunno.....

FWIW - some stock cranks live into the mid 9's without issue. I know of one personally....... however.....detonation or pre-ignition....... could happen at any time...... or could have "almost" broke on a previous "blast" and actually come apart later..... like in this case.... merging on the highway....

IMHO.... if you can afford it..... get the good stuff...... if you can't.... be prepared to listen to the music when it lets go...... (I'm building a low 10 sec capable combo with stock rods and crank ) Mine could "blow or go".....

With that said.... high dollar forged cranks or rods are not immune to detonation caused damage either....

Good luck with your next build....keep us posted....