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Primary Gear Issue Cause And Prevention


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#1 unburntfuelinthemorning

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Posted 02 February 2020 - 07:25 PM

I've been having clutch drag issues and have been chasing and fixing different things but the drag came back worse than ever even with the external mechanism appearing to be working normally now. 

 

Took the engine out to investigate and found I could hardly turn the primary gear and oil seal was leaking despite both parts being almost new.  Primary gear was quite hard to remove and had what looks like conjealed oil inside.  Crankshaft thankfully looks fine.  Cleaned the oil out and it slides back on no problem and turns properly however the bush closest to the block has had it. 

 

What has caused this and how do I make sure it never happens again?

 

B3SJLpj.jpg

 



#2 Moke Spider

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Posted 02 February 2020 - 07:42 PM

What's the other bush look like ?

 

<edit: can you post up a photo of that and the tail of the crank ? >


Edited by Moke Spider, 02 February 2020 - 07:48 PM.


#3 sc-em

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Posted 02 February 2020 - 07:55 PM

Looks like it has been scoured. Any filings in there? Does the idle gear spin okay with the end cover on? Failing that, it's a faulty bush. They are only soft but should not look like that.



#4 absx2

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Posted 02 February 2020 - 08:40 PM

I picked up a NOS primary gear and cooked it in clean engine oil at 75 degrees C for a few hours, I believe that`s the best thing to do with Deva bushes but i`m not sure if new primary gears use the same material although its not going to hurt anything.

Even at the lower clearance spec the primary gear can seem a little sloppy as a lot of heat can go through them when revving the car with the clutch in but that one looks like it was tight and dry. 



#5 pogie

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Posted 02 February 2020 - 09:02 PM

The bush on my straight cut primary drop did the same.  Apparently they are notorious for picking up and spinning in the gear and the advise from MED was to to remove the damaged bush and fit a floating one.   https://www.minispar...px|Back to shop


Edited by pogie, 02 February 2020 - 09:03 PM.


#6 unburntfuelinthemorning

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Posted 02 February 2020 - 09:14 PM

What's the other bush look like ?

 

<edit: can you post up a photo of that and the tail of the crank ? >

Other bush is fine, crank is discoloured but totally smooth.

 

62J0P4E.jpg

 

iytAdB2.jpg

 

Looks like it has been scoured. Any filings in there? Does the idle gear spin okay with the end cover on? Failing that, it's a faulty bush. They are only soft but should not look like that.

No filings.  I'll try idler with the cover on but I did set the clearance properly.

 

I picked up a NOS primary gear and cooked it in clean engine oil at 75 degrees C for a few hours, I believe that`s the best thing to do with Deva bushes but i`m not sure if new primary gears use the same material although its not going to hurt anything.

Even at the lower clearance spec the primary gear can seem a little sloppy as a lot of heat can go through them when revving the car with the clutch in but that one looks like it was tight and dry. 

Mine too was NOS and cooked in oil although I'm wondering if I got the oil too hot.  It span lovely when I put it together a few months ago.
 



#7 Moke Spider

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Posted 03 February 2020 - 07:22 AM

Cheers for the photos.

 

It looks to me like the clearance on that bush was on the tight side from the start and with a bit of extra temp, it's picked up. Do you recall what it was ?

 

Cooking them in Oil is the way to go. You wouldn't have gotten it too hot in the oil - unless the oil was on fire ! I let mine soak at about 80c for about 4 hours.

 

You ca re-bush that end OK. The original Glacier Bushes for that end are still available.



#8 ACDodd

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Posted 03 February 2020 - 12:35 PM

As Moke said clearance too tight.

Aim for 0.005" with the modern bushes.

Ac

#9 unburntfuelinthemorning

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Posted 03 February 2020 - 02:26 PM

Well I think I cocked up checking the clearance.  I have 2 thou written down and I don't know why as I asked the question last May in this thread and found out the clearance should be 3 to 4 thou.

 

Was it common to have to machine new primary gears before use?

 

Not sure whether to use one of the old gears if it's serviceable. 



#10 Moke Spider

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Posted 03 February 2020 - 06:25 PM

Well I think I cocked up checking the clearance.  I have 2 thou written down and I don't know why as I asked the question last May in this thread and found out the clearance should be 3 to 4 thou.

 

Was it common to have to machine new primary gears before use?

 

Not sure whether to use one of the old gears if it's serviceable. 

 

Ah, OK,well,,, that's the issue.

 

999 times out of 1000, the new factory gears would 'fit' out of the box, however some I've had, have had excessive clearances (one was 0.014" !). All the same, measure and never assume (and yes, I know you did this).

 

I know this has now made you doubtful of what to do and which way forward.

 

If it were me, I'd be happy to re-bush (fit a Glacier brand Bush), machine it to 0.0035 - 0.004" and go again. I don't think you have a lathe (?) and so you'd be going to a machine shop to have this done. They will really want to measure the crank with their measuring gear to be sure if getting it right. You don't need to use an Engine shop for this, but just a firm who does general turning work.



#11 unburntfuelinthemorning

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Posted 03 February 2020 - 06:51 PM

Ah, OK,well,,, that's the issue.

 

999 times out of 1000, the new factory gears would 'fit' out of the box, however some I've had, have had excessive clearances (one was 0.014" !). All the same, measure and never assume (and yes, I know you did this).

 

I know this has now made you doubtful of what to do and which way forward.

 

If it were me, I'd be happy to re-bush (fit a Glacier brand Bush), machine it to 0.0035 - 0.004" and go again. I don't think you have a lathe (?) and so you'd be going to a machine shop to have this done. They will really want to measure the crank with their measuring gear to be sure if getting it right. You don't need to use an Engine shop for this, but just a firm who does general turning work.

 

I don't have a lathe and don't really want the hassle of trying to find someone to do the machining.  There used to be someone in every town but that doesn't seem the case anymore. 

 

I only fitted a new old stock gear as it seemed prudent at the time but I'll make sure to get it sized and machined properly if I do that again.

 

I've just measured everything again.  Crank is 1.498" or 1.499" depending which mic I use.  Using a telescopic gauge I'm getting 1.500" on the rear bush of that primary gear which doesn't leave much clearance.  I have two old gears, one measures 1.503" on both bushes and the other measures 1.504".  I'm thinking the one measuring 1.503" will do the job.  Does that sound reasonable?



#12 Moke Spider

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Posted 03 February 2020 - 07:24 PM

I don't have a lathe and don't really want the hassle of trying to find someone to do the machining.  There used to be someone in every town but that doesn't seem the case anymore. 

 

I only fitted a new old stock gear as it seemed prudent at the time but I'll make sure to get it sized and machined properly if I do that again.

 

I've just measured everything again.  Crank is 1.498" or 1.499" depending which mic I use.  Using a telescopic gauge I'm getting 1.500" on the rear bush of that primary gear which doesn't leave much clearance.  I have two old gears, one measures 1.503" on both bushes and the other measures 1.504".  I'm thinking the one measuring 1.503" will do the job.  Does that sound reasonable?

 

As well as measuring in the way you have, I also do a 2nd 'check' with feeler gauges. I have a set that is narrowed and ideal for doing checks like these. The Feeler Gauges are not really a measurement as such, but just a means of getting a 'go - no go' for clearances and a check on the measurements made (to a point).

 

In regards to which used gear to use, I'd suggest also checking with feeler gauges for clearances. Check in a few places and plains in case the crank and / or the bushes are out of round. Also check the condition of the 'top hat' of the back bush and the condition of the gear teeth.
 



#13 unburntfuelinthemorning

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Posted 05 February 2020 - 06:37 PM

I can get a 4 thou feeler gauge between the gear and the crank.



#14 AP2020

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Posted 05 February 2020 - 06:51 PM

using a lathe for this type of bush is not the way to go,..

 

It should be honed, as honing is far more accurate and is far better at producing round holes than a lathe ever will. but also creates a cross hatch pattern that is much better at oil retention, there will always be a little oil escaping between the tail and bush.

 

The larger the clearance the more oil that can escape, so too loose and you get oil leakage, too tight and you get seizing and resultant damage. 



#15 unburntfuelinthemorning

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Posted 05 February 2020 - 07:07 PM

using a lathe for this type of bush is not the way to go,..

 

It should be honed, as honing is far more accurate and is far better at producing round holes than a lathe ever will. but also creates a cross hatch pattern that is much better at oil retention, there will always be a little oil escaping between the tail and bush.

 

The larger the clearance the more oil that can escape, so too loose and you get oil leakage, too tight and you get seizing and resultant damage. 

The new old stock gear I used didn't appear to have any honing markings on it.

 

 






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