Hello, I'm a long time stalker of the forum.
I have the chance at buying a 'cheap' 1988 MC18 (13000 miles), however the bike has stood for years, and I'm assuming that it's going to need the engine rebuilding.
My question is, if the centre crank seal is toast, what realistically are my options, if any?

Thanks
Rich

I'm guessing that there are no solutions?

Andy should pick up this post. GT engineering rebuild cranks. I had my spare crank rebuilt last year. It depend on the availability of bearings
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Why do things simply when you can complicate them

Thanks, Rob.

As Rob says, we rebuild cranks, and have bearings in stock. As you pointed out however, the problem point is the unobtainable centre seal. That being said though, we have found that more often than not, the 87~88 (MC16 & MC18 Mk1) centre seals have been good enough to reuse.

As a caveat to the above though, modern fuels appear to be taking much more of a toll on 2-stroke crank seals, and as such, I expect to see fewer 87~88 cranks suitable for rebuilding in coming years. The last two MC21/28 cranks for example, have had the centre seals literally disintegrate as the cranks were pressed apart!


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Andy.
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Thanks for the replies. I'm going for a proper look tomorrow.
It seems really sad/bad that such a small thing can be such a barrier to keeping these bikes on the road.

As I say, so far, we've been able to rebuild more than we haven't. The problem is unless there are real, obvious signs of damage on the centre seal (we have seen them chewed up before), you can't be sure they will effectively seal until the crank is back in, and the motor is built.

Therefore, every 87~88 crank rebuild is done with an understanding by the client that there's a certain element of risk. It is understandably an expensive risk, but it's not just a case of casually throwing the seal back in. We would still scrutinise it as best we can, before making the decision to continue.... you just can't ever guarantee it.
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Andy.
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Thanks for your reply Andy. I didn't get chance to have a look today, hoping to go tomorrow.
Is it worth doing a leak test before taking the engine apart, sorry if I sound a bit dense, the last two stroke I had was an AR125 in 1992!

Yeah, it's worth doing, but may just show up a bad outer seal before the centre gives up.

In fairness, we've seen bikes that have stood for years given a splash of fuel and a new battery, and fired right up! It's hard to comment really, unless the bike is sat right in front of us. Sometimes [when it's your own kit] you just get that feeling of "yeah... it'll be alright!", and you just go for it!
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Andy.
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Thanks, I feel at lot more confident now.

not sure if the cranks is same as 1989 ?? but I found a pic on google image of a '89 crank fiche/diagram. shows centre bearing koyo 68od x 28id x 19 part no (83c137ejh2-9tcs39) and centre bearing seal Honda 67 x 1 part no (91301-kv3-771).
The seal is available from fowlers parts.co.uk £1.51 +vat postage etc.. hope so as this post has me worried, I'm just about to buy a low mile mc18

[a] It's not the same as an 89 crank.
[b] That seal is an O-ring.
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Andy.
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Andy do you think the damage is being caused by the high ethanol content in regular 95 Ron fuel? I fill up my bikes with super unleaded just because I've heard lots of horror stories about ethanol eating away at seals, plastic tanks etc.

Almost certainly due to the ethanol content, Kieran.
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Andy.
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So are the seals available for the '89?

The centre seal is integral to the bearing on the '89 cranks (same as the 90~97 cranks pictured above).

The outer seals are available from Honda still, as is the thin centre O-ring, that sits around the outside of the centre bearing.
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