HI All

I am wondering if anyone can help me with an issue? I have a MC28 Sp Rothmans honda nsr 250 and the lower barrels runs hotter than the top one. I had an issue 2 years ago where I left the fuel on and it filled both Barrels. I removed the exhausts and cleared all the fuel but the water temp ran hot and was erratic. I put this down to the fuel destroying the head gaskets and the combustion entering the water spaces so I changed the following.

New plugs
head gaskets
fresh coolant
new air filter
cleaned jets in carb and checked floats
flushed fuel tank
checked thermostat operation
checked water impellor operation

I Have had the bike for a while and I know somethings not quite right there is slight white smoke from the exhaust too. I may change the plug again as it maybe faulty and should probably replace the exhausts gaskets. I can't think what other areas I can investigate. it may just need a good ride to get things going again but am too afraid to use it knowing there is an issue.

Can anyone help?

Thanks

Ian

perhaps do a leak down test to see if they are holding pressure. if not then the petrol could have damaged the crank seals.

Yeah that's a good idea! worst case scenario with the crank seals though! can only cross my fingers! Thanks for the advice.

White smoke can be caused by burning transmission oil, which can indicate a bad RHS crank seal.

If the idle RPM is higher than usual, or erratic, it can indicate a bad LHS or centre (or both) seal. Spraying a little carb cleaner towards the rear of the flywheel while the motor is running will often see the the RPM rise as the combustible cleaner is "sucked" into the crankcase via the LHS seal.

I am a firm believer than modern fuels are very destructive to the crank seals, and it's highly likely they will all need replacing. The integrated centre seal is particularly weak and susceptible to failure on 1989-1997 models.

Unfortunately, if the centre seal is failing it will mean a crank rebuild/new crank, if that is indeed the case. We've seen new [89-97] centre seals fail within just a few years since the introduction of [more and more] ethanol in fuels. (The MC16 & R2/4J doesn't seem to suffer anywhere near as much.)

How do know the lower barrel is running "hotter". Are you simply judging by feeling for the heat differential of the exhaust gasses on your hand once the engine is up to normal operating temperature, or do you have access to in an infra red temperature gun?

A leak down test would indeed be a good idea, but to be honest, I would prepare for the worst. The seals (particularly the centre) just don't last, and if they're already a few years old, and have previously been "immersed" in fuel, I would put money on, at the very least, the centre seal being buggered. Sorry.
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Andy.
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Hi Andy

Thanks for all the advice I will try spraying the cleaner by the flywheel and see what happens. The bike sounds great and runs well at idle, the rpm is fine. the gearbox oil could explain the white smoke as its not too much air something is burning off.

I have an infrared heat gun that's how I know its hot. The top left barrel just at the start of the exhaust reaches about 90 degrees after a few minutes running where as the lower one reaches 130 degrees. They don't get much hotter after riding.

also I have striped and cleaned the power valve on the lower barrel it may have seized and the wires were full of gunk these have all been freed up now but haven't had chance to refit back due to young kids. So will be interesting to see what happens after that.

To be honest though I am expecting the worst. Any ideas what a crank rebuild will cost at GT's in Plymouth?

Ian

If the bike runs OK on idle, then you may be lucky. They can hang on to revs or hunt on idle if the centre seal is bad, and also be a pig to start, but often run fine through the gears once started. But various conspicuous idling issues almost always gives it away.

To be fair, I've never had an infra red gun on NSR barrels, but a 40° difference is rather significant!

A rebuilt crank is about £500 if the crank passes [a £25] assessment (most do, but some do not). I believe GTPE have brand new cranks in stock for about £650.

I've not worked there for 18 months now, so best to get in touch to double-check prices and lead times. Please tell them you were referred by NSR-WORLD if you contact them.
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Andy.
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Just to update new cranks are 710£ from gt performance.

Thanks to you both. Yeah the bike starts first kick, idles well and runs well. I think if it wasn't for the fact that I'm an engineer I probably wouldn't pick up that something was wrong.

The erratic temp originally I believe was the fuel damaging the head gaskets as once they were changed the temp characteristics were better and increased slowly again.

Originally the fuel leaked through and as I kick started the bike it hydraulically locked, I tried again as didn't suspect this and forced all the fuel out through the exhausts so maybe the fuel didn't reach the crankcase? or maybe little did and didn't reach up to the seals? (I'm hoping). I'm not sure how long it could have been like this for it was 2 years ago and I remember starting the bike frequently but also had a baby and was studying.

The possibly seized power valve could answer the question of the smoke from the right exhaust when opening up but doesn't explain the high temp at idle.

I will carry on and update you when I'm done and let you know. if the power valve doesn't work then I will go for leak down test.

Thanks

Ian

Yes let us know. You never know you could be lucky.

George1980sproth wrote:
Originally the fuel leaked through and as I kick started the bike it hydraulically locked, I tried again as didn't suspect this and forced all the fuel out through the exhausts so maybe the fuel didn't reach the crankcase? or maybe little did and didn't reach up to the seals? (I'm hoping).

By virtue of the design, "crankcase reed valve induction", the fuel must have entered the cases first.
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Andy.
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of course it does! how silly of me.

George1980sproth wrote:
of course it does! how silly of me.

Sorry, I couldn't help myself!
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Andy.
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I'm blinded by hope!

George1980sproth wrote:I'm blinded by hope!

aren't we all lol
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John 3:7

I won't tell you what I'm blinded by!
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Andy.
NSR-WORLD.COM

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