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Excessive crankshaft end play

General engine tech -- Drag Racing to Circle Track

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1972ho
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Excessive crankshaft end play

Post by 1972ho » Sat Mar 21, 2020 12:45 pm

What are the causes of crankshaft end play over the maximum and is there a way to reduce excessive end play rather than replacing the crankshaft.

Momus
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Re: Excessive crankshaft end play

Post by Momus » Sat Mar 21, 2020 12:59 pm

What is the engine?

Wear and bad grinding tolerances.

Some engines have oversize thrust bearings.

There are shaft repair methods.

jed
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Re: Excessive crankshaft end play

Post by jed » Sat Mar 21, 2020 7:55 pm

Just move the thrust cap foreword or back to get the thrust clearance you want.

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Re: Excessive crankshaft end play

Post by BillK » Sat Mar 21, 2020 8:27 pm

jed wrote:
Sat Mar 21, 2020 7:55 pm
Just move the thrust cap foreword or back to get the thrust clearance you want.
ABSOLUTELY NOT !!!!!!! You need the entire surface of the thrust bearing hitting on the crankshaft when it is being pushed forward. If you dont you will only have half the thrust surface available !!!!!
Bill Koustenis
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Re: Excessive crankshaft end play

Post by BillK » Sat Mar 21, 2020 8:29 pm

Depending on the engine type there might be overlength thrust bearings available but that will require regrinding the crankshaft to the correct size.

What type of engine and how much over the spec is the movement ?
Bill Koustenis
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1972ho
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Re: Excessive crankshaft end play

Post by 1972ho » Sat Mar 21, 2020 9:10 pm

Wow Jed what do you mean by move the thrust cap forward are backward its fixed.This a crank that has just been ground and I remember the crank grinder say he needed to kiss it a little.And it is only about .0005-to .001 from Max allowable.

65dragster
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Re: Excessive crankshaft end play

Post by 65dragster » Sat Mar 21, 2020 9:55 pm

It probably won’t help, but I lost the thrust on a 327 in a mid-11 second bracket drag car. I used a torque converter from my friend’s dragster which used an engine plate. I failed to have the mounting surface adjusted and over the course of a season, it killed the crank thrust. I was able to have it welded and remachined and it worked for years afterwards.

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Re: Excessive crankshaft end play

Post by jed » Mon Mar 23, 2020 9:40 am

There are many import engines 4 and 6 cylinder that have only 1/2 a thrust bearing usually located in the block. With a turbo these engines can make 200/250 hp per cylinder and have no thrust bearing problem. And there are modern present day V/8
and V/6 engines setup the same way with only 1/2 a thrust bearing.
Last week I put a cast iron LS 6.0L together put the main bearings in the block then dropped in the crank and checked the thrust it had .0065 thrust. I thought great t wouldent have to jack with sanding the cap thrust bearing. Not so I barley had .002. I pulled the cap measured the 4 segments of the thrust bearing side to side and they varied from .090 to .094. King race bearings. I sanded the thrust till I got .005 and let it go.
Was the thrust of the crank touching the upper or lower bearing???

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Re: Excessive crankshaft end play

Post by Momus » Thu Mar 26, 2020 2:05 am

jed wrote:
Mon Mar 23, 2020 9:40 am
There are many import engines 4 and 6 cylinder that have only 1/2 a thrust bearing usually located in the block. With a turbo these engines can make 200/250 hp per cylinder and have no thrust bearing problem. And there are modern present day V/8
and V/6 engines setup the same way with only 1/2 a thrust bearing.
Last week I put a cast iron LS 6.0L together put the main bearings in the block then dropped in the crank and checked the thrust it had .0065 thrust. I thought great t wouldent have to jack with sanding the cap thrust bearing. Not so I barley had .002. I pulled the cap measured the 4 segments of the thrust bearing side to side and they varied from .090 to .094. King race bearings. I sanded the thrust till I got .005 and let it go.
Was the thrust of the crank touching the upper or lower bearing???
Conversely there are engines that need an enlarged full circle thrust bearing if they are running a manual transmission and a high force clutch springs.

No hydrodynamic lube on a thrust bearing.

I have contemplated using high tensile bronze alloy ring screwed to the main cap/bulkhead for one engine with excessive clearance

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Re: Excessive crankshaft end play

Post by MadBill » Thu Mar 26, 2020 10:07 pm

A shop I frequent had a Trans Am Corvette a few years back that failed its thrust bearing and chewed up the crank due to a ~ 20 lap yellow* behind a pace car that was so slow the racer had to keep dipping the clutch to keep his speed down. #-o (*a broken brake rotor started a grass fire.)
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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