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For specific matters pertaining to the smoking thundering twins

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Postby Vince2 » Sun Jun 24, 2012 10:29 am

I'm a newbie on this board and wanted to say hi. :)
I just bought a 1968 Cobra with a number in the 10800's. It's just been imported from the States and in a poor but 95% complete state.
Wasn't going to take it appart till the winter but could help myself. :roll: I've started stripping it as it had a standing sieze on the left piston. Managed to free it off and clean up the bore fine. Actually the pistons, bores and rings all measure up well within tolerance of standard bore. I'm real pleased about that as it's been stood for years outside. (Im still pulling grass off it!! :lol: )
I know about the gearbox oil level needing to be increased to 1400cc but how can I check if the conversion has been done without pulling the cases appart?
When I drained the oil, next to nothing came out :o Also, did I do wrong by taking out the bolt next to the gearbox oil drain bolt? the one with a long thread and a domed top?
I'll upload some pics of the strip as I do it if anyone thinks it's worth seeing??
Hope someone can help. I don't want to strip the cases unless I have to (Or it's easy)
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Re: New member

Postby johnakay » Sun Jun 24, 2012 4:47 pm

Hi and welcome.
answer to your question is no.
you will need to split your engine,the chance's are it will not have been done.
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Re: New member

Postby Vince2 » Sun Jun 24, 2012 10:06 pm

Thanks for the advice. Had a quick look at the Haynes manual. Will I need a puller?

Also, what happens if I put in 1400cc into a gearbox that hasn't got the mod? Where does excess end up?
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Re: New member

Postby Batterstyle » Wed Jun 27, 2012 10:39 am

I would not rush to strip it down. Get it going and ride it (with 1200cc of fresh grear oil). That was you can listen to the engine which will give you clues to what to fix if and when you strip it down. It should be quiet with no horrible rattles or rumbles. When you are going down hill change down gears with no throttle. If the little end is worn it sounds like a can with marbles rattling around. Check the gear change. It should be positive with no false neutrals. Neutral should also be easy to select. If you need to push or prod the gears the selectors are probably worn or bent. Listen to the gears. If the case hardening is worn off the gears you will know, it sounds like a freight train under you.

While you ride it check the gearbox oil oil every ride. Monitor the exhaust smoke out of each pot. Get the bike tuned. If you have any of the above problems or if the gear box oil is going down a strip down is a MUST. If you are lucky and the engine is not drinking gear oil and the motor sounds sweet proceed to ride with careful and regular checks . Check the way the plugs are buring and gear oil etc. If these are all fine I wouldn't strip it just to upgrade the gear oil level to 1400cc. The early gear boxes generally only stripped gear case hardening if the bike was flogged or the gear oil level was low thus starving gears of oil. 4th or 5ht were the ones affected as the other gears are only used momentarily. Use a good quality 85W modern oil like Belray Gear Saver. These modern oils are very runny compared to old thick gear oils.

If your engine is all good it is certainy worth more than a rebuilt engined bike. There is somehting about knowing the engine has nor been pulled apart since the factory. I would try to preserve that if possible.

Enjoy that rare and collectable piece of motorcycling history!

Neil, 1973 T500, 1971 T500 racer, 3xTS90,s TS125,TC90, TC125, TC100, 3xRL 250's, TS250ER, RV125, K10 80.
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Re: New member

Postby Batterstyle » Wed Jun 27, 2012 10:42 am

Sorry I didn't answer your question. The drain oil plug is in the middle underneath. I also drain the out one under the clutch. You can just reinsert the one you have taken out. It is the selector drum locator.
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Re: New member

Postby Vince2 » Thu Jun 28, 2012 12:28 pm

Thanks very much for that complete answer. I am definately NOT going to 'restore' it as I too value unrestored bikes - At least unless I have to. Don't mind a bit of rust! Shows it's age nicely.
I'm a distance away just now from getting it running as I want to check out some parts but I'll try to keep you posted if you're interested?
Thought the indicators were missing but on researching a bit see that the early ones didn't have any. Looking under my seat the only thing there is the regulator/rectifier - and that looks amazingly basic!!
The only switch on the bars is for toggling between hi and lo beam. (Low beam on permanently) The switch for it is in the L/R location implying there should be indicators. When appart, there is just the hi/lo switch with white/orange/grey lead sitting in the L/R location. Nothing else (appart from horn)
I Love this bike! :D :D It's so basic and simple.
I had a GT500 back in 1976 and toured Europe on it. Great bike, 2 up and still doing about 45/50 mpg.
Can't wait to get this old girl on the road. :D
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Re: New member

Postby pedro » Mon Aug 20, 2012 8:58 pm

Hi vince, there is a uk expert and spares available, pete at tr500.co.uk
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Re: New member

Postby Vince2 » Tue Aug 21, 2012 9:55 pm

Thanks Pedro, I'll give him a call.
I've got the engine back together now (Still nice and filthy!!)
Distracted by a cup of coffee yesterday I connected a new battery round the wrong way. :roll: Sparks ensued from the positive terminal towards the recifier for about 2 or 3 seconds before I took the lead off. Have I wrecked the rectifier or regulator?
Fuse hasn't blown.
I'm trying in vain to get the new B77HC spark plugs to spark and I don't know if It's as a result of my error or something else.
(I don't know if it was working previously)
Points seem ok.
Any static tests I can do to check the alternator/rectifier/regulator?
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Re: New member

Postby al249v » Tue Aug 21, 2012 11:15 pm

Hooking the battery up backward can damage the regulator and/or rectifier, but the ignition system is mostly separate from the charging system. The best test I've come up with for initial diagnosis of the ignition is to remove the plugs, connect the plug wires, lay the plugs so that the bodies make a good ground, turn the motor so that the points are closed, turn the key on and then manually open the points. All that is involved at that point are the plugs, plug cables, coils, points and condensors (assuming that the battery has a good charge). If opening the points doesn't produce a spark, check that the points are actually closing by shorting across the point contacts with a small screwdriver, when you remove the screwdriver you are effectively opening the points. If that doesn't produce a spark, I'd then check to make sure the + side of the coils have 12 volts, you may have a wire broken somewhere. If you have 12 volts at the coils and the points are definately opening and closing (confirmed with an ohm meter) then check the condensors, then the plug wires, then the coils. My bet is that your points have glazed over and aren't opening electrically, even if they are opening mechanically.
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Re: New member

Postby Vince2 » Wed Aug 22, 2012 12:37 pm

Great advice on the sparking. I checked it through and althouth the breaker points looked ok, neither of them were passing current.
I carefully filed both clean and hey presto a good spark at both plugs. :D :D :D
Next job now. De-rusting the inside of the tank. I'm using a crystal/water mix I got off the internet after reading about it on the Kawasaki Triples site. If it's successfull, I'll post details.
Jobs still to do include petrol tap overhaul (I've done this several times on Kawa triples which is VERY similar) Always the tiny o ring in the diaphram area. Not sure if it's available as a Suzuki Part but I'll bet it's the same as the Kawasaki.
Fill gear box oil.
Fit new rear brake shoes,
New tyres front and rear.
Set up front brake - something I haven't done before on a twin leading shoe.

By the way, I measured the tank at about 15 litres. Couldn't find this info anywhere as I assumed the Cobra has a different tank to all other 500's.
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