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Primary Gear Health Check


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#1 JonnyAlpha

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Posted 12 April 2020 - 05:52 PM

Hi;

 

I thought, due to its critical nature, I thought I'd post this particular question up outside of my project thread.

 

All if the questions revolve around the Primary Gear (or at least I think they do)

 

Today I have been going through the various containers of parts from my forthcoming engine build. Some of the parts have not been touched since I stripped the engine and I needed to find out which still needed cleaning / inspecting and which parts can go again or need replacing.

 

In amongst these parts (carefully packed away) was the Primary Gear. 

 

I have inspected the Primary Gear and on the outside it looks fine (I am not a mechanic, nor an experienced Engine builder).

However on the inside there is some slight marking (looks a lot worse when zoomed in though).

 

Here is the Primary Gear:

 

BURwTvN.jpg

 

And on the inside there are some visible rotation lines, the one towards the rear can be felt with a finger:

 

IPudCOH.jpg

 

KPLnTRf.jpg

 

Questions:

 

Before we embark on the bushing I need advice on the following:

 

Flywheel / Primary Gear Compatibility (No of Teeth)

I bought a MED Engineering ST1 Verto Ultra Light Flywheel and Clutch Kit which meant I needed to change from an Inertia Starter Motor to a Pre Engaged Starter Motor. The reason for change was that the original Flywheel had a different amount of teeth than the MED Ultra Light one. The ultra light flywheel has 129 Teeth designed to marry up with a 9 Tooth Pre Engaged Starter. The Inertia Starter from the Metro Engine had 10 Teeth (can't remember how many teeth the original Metro one had).

 

Will this change in Flywheel now mean that the Primary Gear is no longer compatible - and what about the drop gearing (if that's what it's called)?

(whilst eating my dinner I was trying to picture how it all connects and the teeth on the flywheel are no where near the Primary Gear :-)

However does it still make a difference? 

 

Primary Gear Bushing

I have read this 3 year old post regarding Primary Gear bush damage, if the Primary Gear is compatible, in your expert opinion is this bushing OK or if not, can it be replaced? E.G. by fitting a new 'floating' bush

 

Oil Inside the Wok

Not sure if this is an associated or separate issue, I recall that when I first stripped the engine to move it to my garage, when I removed the Wok, the inside was coated with blackened oil. I understand that oil in the clutch housing = major problems, but what would have caused this and what should I do to ensure the problem does not manifest itself during the rebuild.

 

Reading Kieth Calver's article on Primary Gear Problems here, a failed / failing bush / problem Primary Gear Bushing can cause oil to move through the primary gear, but I guess this will only leak into the transfer case and not into the Clutch Housing? So what's the probably cause of oil in the clutch housing?  

 

Here's a pic from when I first stripped the engine, you can see the oil (the engine had not been run for about 15 years):

 

8WTVR65.jpg

 

Help and advice needed on all of the above - thanks


Edited by JonnyAlpha, 12 April 2020 - 06:05 PM.


#2 alex-95

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Posted 12 April 2020 - 06:50 PM

The primary gear should be fine for compatibility as it's the clutch that goes onto the splines on the gear.

 

The bush I think needs replacing, would need to be checked for size compared to the crank to see if it's still within tolerance even if the bushes looked good. I've used the minispares bushes thats not recommended by mokespider :o (bought and fitted before that thread I think), Just from my experience they seem to be ok. They need to be bored out on a lathe, not sure on the sizes but you'll need to have the crank measurement to be able to get it done.

 

The oil in the wok could be from the primary gear being scored or oversized and then seeping through the gear into the wok side, more than likely just the seal. where the seal runs on yours, it looks a bit rough? If it's not dead smooth that that will cause it to leak.



#3 DeadSquare

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Posted 12 April 2020 - 08:01 PM

The primary, or Diva gear, only rotates on the crank tail when your foot is on the clutch, so I wouldn't worry too much about the marks in the rear bush, but the mark made by the red oil seal is a more serious problem as it is very likely that the life of a new seal will be compromised.



#4 JonnyAlpha

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Posted 12 April 2020 - 08:30 PM

The primary, or Diva gear, only rotates on the crank tail when your foot is on the clutch, so I wouldn't worry too much about the marks in the rear bush, but the mark made by the red oil seal is a more serious problem as it is very likely that the life of a new seal will be compromised.

 

Hence the reason for me posting the pic :-)

 

I mocked up this comparison, my gear is on the left and the mark I think you are referring to is labelled with a yellow arrow. Compare it to the pic of a new gear I found online and the whole area should be smooth.

So that indentation has been caused by the oil seal, what could cause that in case it's something else I need to worry about?

 

8jeUcYv.png

 

So a new Primary Gear (or good SH one) then :-( 



#5 DeadSquare

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Posted 12 April 2020 - 08:46 PM

Someone, like Mr. Dodd might be able to lightly grind that out.



#6 alex-95

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Posted 12 April 2020 - 09:34 PM

Yeah that can be ground, maybe even some emery paper.



#7 Spider

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Posted 12 April 2020 - 10:46 PM

It's toast.



#8 JonnyAlpha

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Posted 13 April 2020 - 10:14 AM

It's toast.

 

So what are my options:

 

New Primary Gear? 

Second Hand Primary Gear?

Get mine reconditioned?

 

Also - what would have caused this damage, just to make sure I avoid it in the future (this engine has been completely stripped, rebored, crank ground and balanced etc).



#9 ACDodd

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Posted 13 April 2020 - 11:52 AM

Contact John at Guessworks he can regrind the seal surface. He can also rebush the gear.

I do rebush many gears for the trade and also make my own heavy duty front bushes. Currently not able to regrind the seal surface.

Ac

#10 Pigeonto

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Posted 13 April 2020 - 06:41 PM

You don't have to run the new seal on that groove. The seal track seems rather a long way in anyway, meaning the seal may have been fitted too far in.

There's plenty of engines get built with the seal fitted in such a way as to be running on an un-worn part of the seal surface.

Just another ( and cheaper) option 



#11 JonnyAlpha

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Posted 13 April 2020 - 09:13 PM

Contact John at Guessworks he can regrind the seal surface. He can also rebush the gear.

I do rebush many gears for the trade and also make my own heavy duty front bushes. Currently not able to regrind the seal surface.

Ac

 

Yes been in touch. He can Recon it for about £80- £90



#12 JonnyAlpha

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Posted 13 April 2020 - 09:15 PM

You don't have to run the new seal on that groove. The seal track seems rather a long way in anyway, meaning the seal may have been fitted too far in.

There's plenty of engines get built with the seal fitted in such a way as to be running on an un-worn part of the seal surface.

Just another ( and cheaper) option 

 

I cleaned it up today with some brake cleaner.

 

The groove is quite small - looks worse in the pics because its shiny and reflects the colours around it. 

 

TdUT882.jpg

 

AwRjeQu.jpg



#13 Spider

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Posted 14 April 2020 - 01:17 AM

 

It's toast.

 

So what are my options:

 

New Primary Gear? 

Second Hand Primary Gear?

Get mine reconditioned?

 

Also - what would have caused this damage, just to make sure I avoid it in the future (this engine has been completely stripped, rebored, crank ground and balanced etc).

 

 

I'd suggest finding a NOS one or a good used one.

Reginding them leaves them undersize and I've seen these give issues as a result.

 

I don't rate the current bushes. When (not if) they give trouble, they'll take your crank with it.

 

Over the years, I recall only ever seeing one Deva Bush seize on the Crank Tail. The Bush was Karput, but the crank was totally fine. These new bushes when they do lock up, will ruin the crank in no time.



#14 Ethel

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Posted 14 April 2020 - 09:00 AM

Wonder if you could make up a spacer to move the seal to run just out of the groove?

 

Don't shoot, just thinking aloud!



#15 JonnyAlpha

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Posted 14 April 2020 - 09:26 AM

I need to get my head around how it all goes back together and what presses you against what. I like to know how things work.




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