2T crankshaft seal failure - what are the signs..?

[A100man]

My GT250 is from 1976 as far as I know it will not have has the seals changed or the crankshaft rebuilt. When I first started to run it I added some seal conditioner to the g/box and the 2T oil since it had been stood for a minimum of 15 years, who knows if t helped..

I've probably put less than 1000 mile on it in the past 3 years since then but it starts OK (always about 4th kick) now I've replaced the coils points etc..

It IS slow on the pick-up however and you need to give it a good handful at the lights to prevent looking an idiot... after that it runs pretty well BUT it tops out at an indicated 75-80 MPH, although I don't think the speedo is off the bike so may not be that accurate

Anyhow when I acquired it I did think it would have to rebuild the crank but now I'm in two minds.. I don't need the top end - I've other bikes for going faster, longer but the (lack of) pick-up is a little annoying.

Thoughts?
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Now: A100, GT250A, XJ598, FZ750

Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600

[MarJay]

Stood for 15 years? It needs new seals.

You could see a few different symptoms. Lack of compression, water in the crank case, oil in the water, loss of gearbox oil etc. Depends on the design of the engine and which crank seal goes first I guess?
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[A100man]

[P.]

When I bought my RS125 it had stood for a year, it started fine, it rode home fine, the next day it was in need of engine work

I'm no 2 stroke smartie, but seals and rubber in general just go bad, they dry out, crack, when in use it'll just give up.

[Pete.]

45 year old rubber seal? Gonna need changing IMO.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[A100man]

I admit I'm probably in denial, but I was also wondering in the symptoms are consistent with crankshaft seal(s).

The lack of top end I can live with - it's the pick-up that is more bothersome
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Now: A100, GT250A, XJ598, FZ750

Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600

[Pete.]

My biggest worry about doing this work would be do the middle seals as that means pressing the crank apart. If you're going to do that you might as well get a replacement middle bearing also.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[A100man]

[blurredman]

Depending which seal is actually leaking symptoms could be different.

As mentioned- gearbox oil disapearing? It is particularly smokey? Can be hard to tell. Drain all the oil and measure- put it back, then give it a few hundred miles I suppose - drain and re-measure? I know a small drop of oil can make a lot of smoke, so can take time to give meaningful reading the 2nd time it is dumped and measured.

Generator side? Idle is good and even and doesn't deviate? If an air leak i'd suspect the throttle might actually be more oomfy due to potential lean condition? At that- might not even be- air leaks can come from the barrel to crankcase connection or carburettor inlet either side of the inlet.


All that said, and ideally old seals that have been left standing isn't perfect. But if it runs fine, doesn't hunt or hang high at idle and the spark plugs look pretty good, and the oil measurement checks out- maybe the carburettor/s just need to be tuned to give you a bit more of what you want?

Raising the main needles just a single notch, or richening the fuel pilot screws can provide possibilities for a more willing take off.. I take it your tune is standard according to the book? Perhaps experiment? Doing small adustments can make a big difference.
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CBT: 12/06/10, Theory: 22/09/10, Module 1: 09/11/10, Module 2: 19/01/11
Past: 1991 Honda CG125BR-J, 1992 (1980) Honda XL125S, 1996 Kawasaki GPZ500S.
Current: 1973 MZ ES250/2 - 17k. , 1979 Suzuki TS185ER - 9k, 1981 Honda CX500B - 91k, 1987 MZ ETZ250 (295cc) - 38k, 1989 MZ ETZ251 - 49k

[redeem ouzzer]

If it's the outer seals then you'll either be burning gearbox oil (or the gearbox oil will smell of petrol), or you'll have oil mist on the generator side. Centre seal failure (unless it dies completely) is hard to diagnose short of doing a leakdown test.

Sounds fucked anyway - my X5 will do 75-80mph, I would expect most vintages of GT250 to be able to show 90mph on the clock.
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Be a REAL MAN!

[A100man]

[MCN]

This is why I prefer shaft drive mowers.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[redeem ouzzer]