MK1 - Possible Rear Crank Gear Play

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camstevens
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MK1 - Possible Rear Crank Gear Play

Post by camstevens »

Rear Crank Gear.jpg
Hi All
I know this is a topic raised before, but I've been suffering primary side knocking and I am eliminating all possibilities. I have addressed clutch and shock absorber issues, but for good measure I though it best to check the rear crank gear whilst all is apart;

The rear gear always was much less tight than the front.....but when I removed it this time I was suprised how little effort I needed to with the puller......I realise the puller thread is fine so lots of torque, but it pulled off without having to "break" the stiction. I don't see any major evidence of fretting (but some corrosion....see pic), and the key is in good condition with no obvious sign of fretting. It is snug in both keyways. Basically i don't think there is any "slop" at all, but more a case of the interference fit not being what it used to be. It may well be a scource of knocking....

I guess I have 2 options;
1. get into the expensive game of picking and matching other gears until I get a tight fit....I could also solve one problem doing this, only to inherit another?
2. Use some quality Loctite-type product to seal gaps and anchor things in place.

If option 2 is feasible, I'd rather go that way.....what product have other used before.....was it a successful remedy?

Cheers
Cam
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Roger Gwynn
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Re: MK1 - Possible Rear Crank Gear Play

Post by Roger Gwynn »

It looks like fretting to me rather than corrosion but difficult to tell in a photo, although your photograph is of excellent quality. The shock absorber is the usual culprit of noise from the primary. I would assemble with high strength Loctite and wear ear plugs. A bit of heat will destroy the glue when it comes time to remove it again. I have used Loctite on main bearings, doesn't work, wheel bearings, it does work but will depend on many factors, size of gap, cleanliness, vibration and heat.
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Re: MK1 - Possible Rear Crank Gear Play

Post by JohnnyBeckett »

him, there is one way we would fix it, but you would have to take the crank out and metal spray the shaft and then grind or turn it to the size you need there is a lot of good engineering shops that do metal spraying :) or they may be able to spray the inside of the gear and do it that way :?: 8-)
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Re: MK1 - Possible Rear Crank Gear Play

Post by camstevens »

Hi Johnny
That may be the route I end up taking, but the engine has just run in beautifully after 1200 miles. Really don't want to pull it apart.......

Cam
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Re: MK1 - Possible Rear Crank Gear Play

Post by MARK.WALSH »

I had the same problem on my square 4 the other year. It ended up being the rear crank coupling and although the cog was difficult to remove there was scoring and wear on the mating surfaces.
I replaced the woodruff key (even though the original one looked okay) Reassembled with Loctite - and no problems since , which is about 800 to a 1000 miles.
Might be worth doing the same as opposed to stripping it down.
Regards
Mark
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Re: MK1 - Possible Rear Crank Gear Play

Post by camstevens »

Hi
Yes, I will use the Loctite as see how I go. From my understanding Loctite 680 seems to be the most approrpiate for round shafts with interference

Cam
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Re: MK1 - Possible Rear Crank Gear Play

Post by JohnnyBeckett »

hi Cam m there is a loctite that we did use for fitting hub bearings in lorries rear axles that was worn and it was very good and stop the bearing rotating in the hub but i cannot remember what the number was, all i remember was it was not the normal stud and bearing fix, it was to take up bigger gaps i think you will need to look at the loctite site and you will find the one you need :)
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Re: MK1 - Possible Rear Crank Gear Play

Post by simon.holyfield »

camstevens wrote:Hi
Yes, I will use the Loctite as see how I go. From my understanding Loctite 680 seems to be the most approrpiate for round shafts with interference

Cam
Which Loctite product did you use Mark?
cheers

Simes

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Re: MK1 - Possible Rear Crank Gear Play

Post by allan.walker »

Good luck, Cam. I hope that you are able to sort this out with Loctite.

My knocking primary may have been spline wear on the rear crank, but having removed the shock absorber and tried the JB Weld fix, the noise continued and grew louder.

I carried-out a quick check whilst the engine was running, by removing each plug cap in turn. (A tip I read recently on this forum.)
When I got to the l/h front cylinder, when I replaced the plug cap it sounded like I'd hit the crankcase with a hammer. I repeated this several times with the same result.
Conclusion: big-end gone on l/h front crank.

At least the strip-down will enable me to fit the missing OPRV ( as mentioned in my other thread.)
camstevens
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Re: MK1 - Possible Rear Crank Gear Play

Post by camstevens »

Wow......it must have been a nasty wear to be that harsh? I wonder how it picked up and wiped....overpressure? I think a big end noise is always there....where my noises can come and go......

With all the best intent and dilgence, these SQ4's can be a heartbreak at times
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