How I finally fixed Triumph pre unit chaincase oil leak - The Jockey Journal Board

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Old 02-29-2020, 06:45 PM   #1
Britiron
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Default How I finally fixed Triumph pre unit chaincase oil leak

I followed several threads on this topic. I use ATF, and even with minimum oil level, high speed rides always ended up with oil getting on the drive chain and then on the rear wheel. This is partly due to the fact that I run without a chain guard.

I tried a phosphor bronze shouldered bush in the large sliding washer, gasket material etc - all to no avail.

As it's heavily modified anyway (including running a longer duplex primary drive chain and unit clutch for years( hint; the unit sprocket has to have the oil seal diameter ground smaller), I decided that I would use the unit engine approach of the sprocket cover with oil seal, fixing the gearbox position and using a unit primary chain tensioner.
I threaded the tensioner spigot 3/8 UNF and used a thinned down nut inside and a serrated stainless flanged nut on the outside
I made an aluminium alloy block (I have a lathe with a milling head) to hold the rear end, keeping the adjuster inside the chaincase. This is fixed in place with 2 x 2BA countersunk screws
I had to cut away part of the alternator mounting to clear the spigot and tensioner blade.
I positioned the sprocket cover having previously set the tensioner and determining the gearbox final position.
I haven't run it yet, as i'm rebuilding the engine. I expect it to work fine but I'll post an update either way.
I've included some pictures and if anyone would like more details just reply.
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Old 02-29-2020, 09:15 PM   #2
Ratso
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Default Re: How I finally fixed Triumph pre unit chaincase oil leak

I expect it to work fine, too: why wouldn't it? That's really good, thanks for the show & tell.
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Old 03-01-2020, 01:13 AM   #3
Thunderbird
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Default Re: How I finally fixed Triumph pre unit chaincase oil leak

good machining skills and approach and I can understand why you did it, but I would rather have gone for a belt drive as solution and dealt with alternator mounting problems.
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Old 03-01-2020, 04:37 AM   #4
Britiron
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Default Re: How I finally fixed Triumph pre unit chaincase oil leak

Hi Thunderbird, thanks for your comments. Yes, I considered the belt drive option, but I've seen that people have had issues with belt shreading failures: maybe down to some belt quality or misalignment. Also, I don't know how well the drive sprocket oil seal seals.Although most belts can be run in oil, the same problem might arise. Finally, how well do clutch friction plates operate / last with no oil?
The person who had the bike before me has drilled two holes through the circular location pad (for the inner chaincase) in the drive side crankcase. It took me a while to figure out why the chain case was filling. I sealed these with epoxy resign and i'm sure it's fixed the issue, but it had added to my paranoia about the rear oil leak. I run a (modified, as it is designed for a T140) racetrack exhaust system, which runs under the chaincase and this ends up with a lot of burnt on oil on it.
I'm an automotive development engineer, so improving designs / reusing other parts is natural to me. I've tried to keep the character of the bike, but improve it. It had been converted to a chopper before I had it, so it was never going to be a concurs original.
The 750 Morgo conversion with 5 speed gears and decent brakes has transformed it. I'm trying to find a dealer for Megacycle cams, who will ship to the UK. I picked this up in another thread, but Megacycle don't do mail order or deal with customers direct. Shame, because their products look really good.
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Old 03-02-2020, 01:58 AM   #5
Thunderbird
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Default Re: How I finally fixed Triumph pre unit chaincase oil leak

I made a very crude seal holder for the pre unit that is holding up reasonably well, if I ever split the cases i'll make a far better engineered seal holder as I think I saw on JJ or was it the gram recently?
my experience with clutch plates is they don't like oil, in the past I've done the thing of soaking in ATF and drying off then using occasional chain lube just to overcome oil leaks, and no, bearings did not fail but then again maybe I didn't run long enough or hard enough.
re megacycle cams; did you try British Cycle Supply up in Wolfville, Nova Scotia.
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Old 03-08-2020, 04:34 PM   #6
Britiron
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Default Re: How I finally fixed Triumph pre unit chaincase oil leak

Hi Thunderbird, just to let you (and others) know, I contacted Mark at Brit Cycle and he has been really helpful. He has the cams in stock and ships to UK, so I'm sorted. Thanks for the hint. Apart from the purchase price, the HM government will hit me for import duty and 20% VAT (sales tax), blood suckers.........
I'm recommend him to anyone, very knowledgeable and helpful
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Old 03-09-2020, 02:35 AM   #7
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Default Re: How I finally fixed Triumph pre unit chaincase oil leak

you shoulda had Goldy ship it to you as a family care package.
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