Technical > Bike Problems/Questions

Has a penny dropped?

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Itsme:
As most people know I have been chasing around oil use by the Mighty Midget GN250 for some time. The latest manifestation is that when left on the side stand the MM smokes quite heavily for up to a minute before clearing. Those of you used to air-cooled BMW twins and early BMW Ks might recognise this symptom from their tendency for oil to run down the left hand cylinder valve guides (or in the case of the Ks the exhaust valve guides which were under the engine) when parked on the side stand.

I changed the valve guide oil seals earlier this year so thought I had sorted that. However just recently I have noticed that valve guide oil seals for GNs are advertised as inlet or exhaust. I didn't know this, maybe I should have, but I didn't so I just bought 4 seals. I decided to check the valve stem measurements today and you may have guessed that the exhaust valve stems are slightly smaller in diameter than the inlet valve stems, hence the different seals!

I now think I may have unknowingly put inlet seals on my exhaust guides thus, in effect, putting worn seals on the guides. This might explain why the engine smokes when the bike has been left on the side stand. There is a fair amount of oil sloshing about inside a GN head as the cam runs in its own sump of oil.

What think you brave Thumpeteers, has my ignorance likely caused the smoking issue? Answers on a used £20 note to my home address.

Ian

CrazyFrog:
Sounds very plausible to me Ian. Ball ache of a job to have to do again, but worth it if it cures the problem!

Itsme:
Thanks Pete, I think it seems like a reasonable explanation for the symptoms I'm getting. As you say it is a ball ache, but as I have Jill's Lexmoto 125 at least I wouldn't feel the need to rush to get mobile again so maybe it would be a good time to try it out.

Of course if it turns out to be not that I might just be leaning towards selling the MM for something a little less environmentally dubious!

Ian

themoudie:
Aye Ian,

Continuing to run the MM, (Bantam impersonator!) is probably more environmentally friendly than investing in a velocipede from the CPR. I suppose an electric cycle might be better, but you wouldn't get the same 'thrum' as that from the powerful MM engine!  ;)

Good health, Bill

Itsme:
Hi Bill

Absolutely right on all counts. I am lucky that my friend Jill, for various reasons, has lent me her Lexmoto to look after for a while and actually prefers me to ride it to keep it in good running order, but I can't think I would put my money that way if it came to selling the MM.

As for being a bantam impersonator that is also a point that I have been considering recently, if I'm going to smoke how about a good old 2 stroke smoke! Somehow though I don't think the reality of going back to a CZ would live up to the dream. The MM does its best to be a proper thumper by having a lot of torque for a small engine, but if I was going to re-visit a machine from my past it would be an SLR 650. The only problem with that is the angle grinder monkeys seem to love attacking them and then asking 6 times what they are worth because they now have no rear end! Don't get me started on that one.

Ian

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