thrust bearing vs. end play - Team Camaro Tech
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post #1 of 10 (permalink) Old Sep 21st, 04, 04:04 PM Thread Starter
 
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I'm wondering if anyone has thoughts on this. I have a '68 El Camino that I bought a few years ago. I was told the engine had about 10K miles on it since a rebuild of some sort. It's just a basic 327. No fancy hotrod setup. The thing ran fine for me for a couple thousand miles, and then it started knocking. I pulled all the accessories and it didn't affect the knocking, so I decided to pull it and tear it down. I've finally gotten around to doing all that. Everything seemed fine with the engine. The bearings look ok, the crank, the valvetrain, the pistons, rings and rods, the oil pump... All that stuff looks fine. Then I went to check the end play on the crank and it came out to about .018, which is of course way out of spec. Out of curiosity, I picked up an old thrust bearing which I had pulled out of another engine and put that in there and checked again. With this other bearing in there, there's virtually no end play. Maybe .002 max. So at this point I'm thinking I'll just buy a new set of bearings and hope the end play specs out ok. The thrust surfaces on the crank look fine.

Anyone think this might not be a good idea? Will excessive end play cause engine knock?

'68 Sport Coupe, '70 Z28, '68 El Camino, '72 Datsun 240z
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post #2 of 10 (permalink) Old Sep 22nd, 04, 01:47 AM
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IMO, it may be a contributing factor. Loose endplay on the rear thrust bearing, larger hole for oil to leak from, less oil delivered elsewhere in the engine, a knock is heard.

Also, with .018" clearance coupled with .014-.016" of sideplay, may contribute some more.

I have never seen/read any dimensions for the width of the rear main journal. I'm sure they get beat on, especially if a heavy clamping clutch is installed behind it. The thrust bearing receives the full push/force from the pressure plate when the clutch is disengaged. You might measure the thickness of each thrust to see if this may be the case.

Crank kits are cheap and there is a warranty. Oil pump is really cheap insurance. Just be sure to check the seal surface for touchup.

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post #3 of 10 (permalink) Old Sep 22nd, 04, 02:53 AM
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Z,
First of all, did you properly "seat" the thrust bearing when you put the new one in ? If not, you will not get a proper reading on end play. You have to put both parts in just like a normal assembly to get the proper end play clearance. Without having heard the "knocking" I really have to question if the thrust was making the noise. I have seen them so bad that the counterweights were almost hitting the main webs, but still not knocking. When they do make a noise it is more like a deep "lub - lub - lub" for lack of a better way to describe it. There are measurements for the rear thrust width on the crankshaft so you should be able to measure it if you have the proper tools, a snap gauge will get you close enough.
Personally, I would stay away from a "crank kit" If you have ever measured one, you would probably never buy one again. Have a good local crankshaft regrinder check your crankshaft and regrind it if needed.
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post #4 of 10 (permalink) Old Sep 22nd, 04, 08:43 AM Thread Starter
 
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I did seat the thing properly. With everything fully torqued down I could easily slide the crank back and forth with my hands. I haven't noticed any evidence of the counterweights hitting the block, but I haven't really looked for it yet either.

How do you measure side clearance? I'm not familiar with this.

Also, what is a crank kit? Just a replacement crank?

'68 Sport Coupe, '70 Z28, '68 El Camino, '72 Datsun 240z
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post #5 of 10 (permalink) Old Sep 22nd, 04, 09:19 AM
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Typically with a crank kit, you give them your crank (core) and they give you another crank with bearings that are supposed to be right. you then install the crank in your engine.

It's basically a used crank that has already been turned and has a set of bearings that come with it.

I have a friend that in high school had a thrust problem so bad he would have to replace the timing chain once every couple months, you could grab the balancer and move it what seemed like an inch. Small block chevy in a 73-74 Malibu. I do not remember it knocking though.

[ 09-22-2004, 11:35 AM: Message edited by: camaroman7d ]

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post #6 of 10 (permalink) Old Sep 22nd, 04, 10:04 AM
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Sideplay is the clearance measured between the connecting rods and side of the journal they are bolted onto. Typically, called rod sideplay or rod clearance.
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post #7 of 10 (permalink) Old Sep 22nd, 04, 02:18 PM
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End play's important, but don't think it'll make a knock, keep looking....





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post #8 of 10 (permalink) Old Sep 22nd, 04, 03:30 PM
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Make sure the crank itself isn't scored on the thrust. If it had a manual trans behind it and was flogged they do score the crank.
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post #9 of 10 (permalink) Old Sep 23rd, 04, 07:38 AM Thread Starter
 
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I don't think it ever had a manual trans behind it, and the crank looks good.

The only other thing I can think of that could have caused the knocking is the fuel pump. Is that a possibility?

'68 Sport Coupe, '70 Z28, '68 El Camino, '72 Datsun 240z
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post #10 of 10 (permalink) Old Sep 23rd, 04, 08:47 AM
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Yes,
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