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Old 7 Jan 2009, 09:40 (Ref:2366881)   #1
Al Weyman
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Too heavy a clutch. could this be causing my engine problems?

I have lost several engines (small block Chevrolet) in recent years due to crankshaft failure usually the crank snapping, this I have been putting down to oil surge despite having a good sump fited (except on one occassion but on that engine I was using a different clutch unit).

Well I have just pulled an engine down after only about 6 races because of a severe oil leak from the rear of the engine and to my disappointment have found that the rear main is shot on the thrust surfaces also damaging slightly the journal although this should clean up OK. The thing is the engine was still showing a reasonable oil pressure and sounded OK so if it had'nt been for the leak I would have carried on using it which leads me to believe this is why I am getting the crankshaft failures. On this engine/car I have been using a triple plate Tilton clutch and I am just wondering is this thing just too damned much for the thrust bearings on this unit as I have no use but to slip the clutch getting it around the paddock and into the workshop as the car is so heavy.

Has anyone else had any experiences of thrust washer failures due to using over heavy clutches on either the Small Block Chevy or any other engine?
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Old 7 Jan 2009, 13:04 (Ref:2367007)   #2
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I have never had any thrust bearing problems but have suffered 3 engine failures due to an out of balance clutch. These have been rear bearings and a broken crank. I now use a Quartermaster triple plate clutch and haven't had any problems apart from a broken a crank last year which I think was related to something else........I hope.
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Old 7 Jan 2009, 15:10 (Ref:2367079)   #3
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http://www.atiracing.com/products/dampers/101/index.htm
Al I have cured this on big engines by fitting a damper.
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Old 7 Jan 2009, 16:34 (Ref:2367124)   #4
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Got one already Gordon, SBC has as standard and this was a steel comp one on this engine. The other engine that let go early last year and uses the same clutch is still in the yard, I think I will pull the rear cap off and have a gander see if the same has happened. The engine I use with a McCloed twin plate is perfect on the thrusts dispite a lot of races.
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Old 7 Jan 2009, 17:16 (Ref:2367149)   #5
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Al. I guessed an old codger like you would have one, but you would be surprised how many people that "play about" with engines don't understand the forces involved. Especially old Mowog 3 bearing junk MGB engines.!!!!!

Incidentally do they snap in the same place ?

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Old 7 Jan 2009, 17:35 (Ref:2367162)   #6
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Yes usually between 3rd and 4th main bearing. The cranks were all balanced as well, maybe I will just have to either put a lighter clutch in or learn to push the thing around the pits and into and out of my workshop.
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Old 7 Jan 2009, 18:55 (Ref:2367212)   #7
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Al, I have run a lot of small block chev cars with tilton clutches never seen a crank snap! as for thrust wear I would be checking your clearance on the release bearing and also making sure the clutch isn't going over centre, I always run a pedal stop and set it up so it just fully releases and no more.
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Old 7 Jan 2009, 19:55 (Ref:2367244)   #8
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I will recheck it thanks.
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Old 7 Jan 2009, 20:22 (Ref:2367260)   #9
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Go to the Tilton web site and look up the release bearing install manuals from memory you should have 0.200" between the clutch fingers and the release bearing with the bearing rite back.

Other thing to check is your damper have heard of them ****ing themselves.
Also what flywheel do you run I always run a tilton. Check that its balanced for your crank some flex plates have a big weight on them!

What brand of Crank?
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Old 7 Jan 2009, 20:41 (Ref:2367267)   #10
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I am using an auto trans flex plate so no flywheel as such maybe this is one of the problems. I am also using the stock Camaro mechanical clutch linkage so plenty of play there. It may be going over centre though as I dont have a stop on it. I just had a look at the old block and crank that broke in the yard and I don't think it was the same problem as the thrust face is undamaged on the crank so maybe I am barking up the wrong tree here, any other suggestions why the thrust faces should be mullered like this.
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Old 7 Jan 2009, 20:51 (Ref:2367278)   #11
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on Jaguar engines if you spin the car without dipping the clutch it puts the clutch cover out of balance which then breaks the crank at a later date . Dipping the clutch or keeping full power solves the problem.
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Old 7 Jan 2009, 20:54 (Ref:2367282)   #12
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Other thing to do is get a tilton bell housing alignment tool and redo the dowels in the bellhousing face (this can cause big issues with a triple plate)
What brand of bearings do you use?
What do you use for a spigot bearing in the end of the crank?
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Old 7 Jan 2009, 21:22 (Ref:2367297)   #13
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I use a needle roller bearing in the crank, actually you have just reminded me of something. I took this engine out of my older car as I have damaged the front bodywork and it had only done half a dozen races I stuck it in my black later model IROC-Z the engine for that is being rebuilt, but when I pulled it out the older car the needle roller spigot bearing had broken up, I wonder if this caused the problem? I only ran it for about 5 slow laps in the later car which has a McCloud clutch which I did change over without rebalancing but was told that it was statically balanced and should'nt really have been a problem on the internally balanced SB Chevy.

Clevite bearings BTW.

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Old 7 Jan 2009, 22:02 (Ref:2367320)   #14
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I would be making sure everything I have mentioned is rite and if the problem keeps happening you may have something odd at play. We had a Trans-am car that kept breaking cam shafts in the end it was the bell housing bound up on a chassis rail what had happened was we had a flywheel explode so we got a full kit (bell housing, starter, flywheel Etc) and they had changed the bell housings slightly. When we bolted the engine in it twisted the block!!!
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Old 7 Jan 2009, 22:23 (Ref:2367335)   #15
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Thanks, I will start by getting the crank cleaned up (its a GM steel crank incidently) I will get them to recheck it for straightness at the same time and reassemble everything carefully and see how it goes, I will also try to avoid driving it around the paddock!
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Old 8 Jan 2009, 20:33 (Ref:2367883)   #16
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you havent spun at some point and stalled and made the engine go backwards have you? the forces would be quite huge.. just an idea?
think it was mentioned above, but are the clutch fingers always slightly pushing the clutch?
i suppose it could be bad harmonics, at normal operating speed the thing vibrates a lot and causes the bearing to wear?
are all the bearings inline? the one 3-4 isnt ever so slightly out of line is it? or the end one i guess?
i guess the crank runs free and easily turned by hand tho, else you wouldnt use it.
just some ideas from and engineering point of view (might be rubbish)
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Old 8 Jan 2009, 20:46 (Ref:2367896)   #17
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I did spin it and put it into the pit wall which is why I pulled it out the car and stuck into the other car but I was not going that fast and it was only a half spin maybe in the crash I may have over pressed the clutch pedal, I will put a stop on that I think. Tell you what though I have just had a new clutch put in my Chevy Blazer tow car and I swear thats as heavy as the racing clutches! I am going away a bit from the clutch theory as I have just checked the remains of the engine that broke a crank and there is absolutely no thrust face damage at all and that unit has done quite a few races with the Tilton clutch, I am going to pull the crank and have it cleaned up and checked for straightness and see where we go from here.
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Old 8 Jan 2009, 21:12 (Ref:2367912)   #18
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Silly but cheap ; get your pet machinist to make you up a spigot bush from a phosphor bronze material . Less prone to total failure than needle rollers , and much easier to change when the time comes !

I can also endorse the clutch pedal stop idea ; hex set bolt with the head against the back of the pedal , two locknuts to adjust it on its mounting plate , and set it so that the clutch just clears when the pedal is fully depressed . Also , there shouldn't be too much free play when the clutch is released ; this can lead to the release bearing being banged about by the clutch plate and the spigot shaft .

That said , I don't think this is the answer , but it does at least serve to remove a couple of variables from the equation .

P.S.: Another silly thought has just occurred to me .... try blueing up the end of the spigot shaft , and trial fit the motor to make sure that the tip of the spigot shaft is not hitting the end of the crank and thus pre-loading the latter once the motor is pulled up tight to the bell housing .
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Old 8 Jan 2009, 21:17 (Ref:2367914)   #19
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the standard Chevy spigot bush is bronze so no problem there, I paid extra to use the needle roller one as thought it was the way to go.
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Old 8 Jan 2009, 22:01 (Ref:2367929)   #20
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We used to use needle rollers up untill this year when we discovered that the spigot shaft was only just in it by 5mm gone back to Bronze, The other thing we used to use was a ball roller in the larger part of the crank.
I would also be checking that spigot length we had a jerico box once that we ordered with T10 length input shaft and it turned up 5mm to long had to make an alloy spacer between the bell housing and box.
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Old 10 Jan 2009, 21:26 (Ref:2369022)   #21
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a phos bronze bush cant break, where as a needle roller bush can.
i think that says it all really!
as long at the bronze bush gets some oil, should last ages, if it doesnt get any oil it will last less long... if u starv a needle roller of oil it wont last very long at all at a few thou revs!
still, that doesnt realy explain anything lol...
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Old 10 Jan 2009, 21:36 (Ref:2369029)   #22
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No I agree after seeing that one broke upso I will put back the standard bush, GM know best!
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Old 10 Jan 2009, 21:39 (Ref:2369030)   #23
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well i wouldnt go that far, it is made in america after all!!
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Old 10 Jan 2009, 23:07 (Ref:2369084)   #24
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Phos bronze is self lubricating, and a spigot bush can't get any oil unless you have a big oil leak from the gearbox. And that would sod the clutch up anyway ! After all its only doing anything when you push the clutch down and put it in gear.

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Old 10 Jan 2009, 23:23 (Ref:2369094)   #25
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Originally Posted by GORDON STREETER
Phos bronze is self lubricating, and a spigot bush can't get any oil unless you have a big oil leak from the gearbox. And that would sod the clutch up anyway ! After all its only doing anything when you push the clutch down and put it in gear.
its only self lubricating if you soak it in oil first , it always used to be 24 hours in a jar of oil or fill it with oil and pressure it through with your fingers either side

did you get my email Gordon?

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