I'm seeking advise:

My NSR has run 46,000 km. The previous (and only) owner had the barrels checked and pistons and rings replaced at 30,000 km and stated the crank "had been checked and was found to be ok" (But how can you check a crank without taking the engine apart?).

I want to revise the engine during the winter.

I have the chance to buy a crank now which the seller claims has only run 3.000 km. Theoretically like new but what abuse has it seen?

At 46,000 km I can probably not assume the crank tolerances are still "within specification", right?

Should I buy the crank even though I cannot inspect it before the purchase or should I have the existing crank overhauled?

I am very indecisive, maybe someone can give good advise?

Thanks!
gepe.

After 46000Km the centre seal will most probably be finished on the crank and the big end bearing cages too.

As for the second-hand crank, can the seller provide proof ? If not, give it a miss as 99.9% of the time the owner will say anything to get it sold.

Your best bet would be to go new as that will last the longest under normal operating conditions.

Best of luck,
Mario

That could be 3000kms of genuine race time! Who knows?!

Your best bet, as far as I'm concerned, is to send us either your crank, or the "3000km" crank, for assessment over the winter, when you won't be using the bike. (Who really wants to ride in northern Europe in the winter?!)

Despite what Mario says, and he should know better, we CAN service the majority of NSR250 (and HRC RS250) cranks, to better specifications than they leave Honda!

We can also build them a damn sight better than other crank builders claiming to do NSR250 cranks, judging by the failures we have both seen, and been informed of. It's just a shame people rarely speak up their satisfaction with our work, or the failures encountered with other people's! And I hear a lot of grievances concerning other vendors too!

Here's one of our more recently rebuilt MC21 cranks, which is now sat in its cases, ready for the top-end to be reassembled and shipped back overseas:



I defy anyone to pull it apart and tell us it's not built better than a stock Honda crank.
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Andy.
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I'm curious why Honda didn't finish the drive side with the copper coating.

The copper plating is added to alter the hardening process. Unplated areas are "harder" than that of the plated areas.
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If I have to take the carbs off once more...

Thanks Mario and Andy for your opinion and advice.
Maybe servicing the crank is a lot better than buying (without proper inspection) a used crank.

Andy, you state the crank has to be assessed to see whether it is servicable and I learn here (http://tech.nsr-world.com/nsr250/mc21/mc21-crank-specifications.php) which measurements must be within certain tolerances:

1. crankshaft journals measured at A, B, C. I understand measurement at B but the arrow to A points to the LHS crank-arm and C points to the end of the crank where a measurement is probably not possible. Also, I don't understand why the measurements are made with the old and worn bearings sitting in the prism blocks. I would have expected that the measurements are carried out without the bearings.
2. Connecting rod big end axial and lateral play: I assume the conrods cannot be replaced with new ones so this is a combination of wear of the conrod and the crank bearing surface?
3. Conrod small end: Isn't this wear also important?

When you re-build the cranks, which bearings are replaced (i.e. included in the 150 GBP set)?
- Crank RHS, LHS?
- Centre bearing? (What type of bearing is this? ball bearing or needle bearing?)
- Conrod big end bearings?

Is there a need to statically or dynamically balance the crank?

Thanks for answers!
gepe.

Well, first off, our £25 assessment fee covers dismantling the crankshaft down to its individual components, and measuring everything with a micrometer to ensure it's serviceable. I am not prepared to give away the numbers on a public forum. In my opinion, our service is unequalled, and we've never had a rebuilt crankshaft fail. We have rebuilt cranks that circulate the Isle of Man every year. Giving away certain information of ours, gathered over around 20 years of working with NSRs would give away our edge. The diagram in Tech section is straight out of the official Japanese Honda Workshop Manual. I'm afraid you would need to have your crank builder interpret it best he can, if you do not wish to use our services.

If the crank is considered rebuildable, then we will quote for the parts necessary. Main bearings are now £200, not £150, and a "basic" crank rebuild is £275 + bearings + return shipping. A "basic" rebuild is still less than half the cost of a new crank from Honda. (Approx £1150) If the crank is not rebuildable, it will be either returned (in component form) at your own cost, or disposed of. We can supply OEM Honda big-end bearing cages and rollers, and thrust washers. Again, the big-ends and cages are not cheap, but in fairness, almost every crank we have done has not needed big-end bearings doing. Generally the big-end crank pins wear or are damaged before the rollers/cages go out of spec.

Our cranks are trued beyond HRC specifications once rebuilt.

I'm sorry. That is all the information I am prepared to share.
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Andy.
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Andy, I was not trying to spy on some of your "intellecual property", I was only trying to get a better understanding of what the total cost of a crank re-build would be, also what you guys are able to fix and where your limitations are.

Well, the perspective that I would get my now still functioning crank back in pieces isn't too tempting, I had hoped to get a good indication of what I can measure before sending the crank and get a 80% reliable picture of the crank.

Well, but maybe that's not possible. I will see what can be done once I have the translated workshop manual.

Btw, the guy selling the 3000 km crank admitted it was used in the "HRC Cup"

The only way to tell is to pull it apart fully, and let's face it, whether a crank has done 3000 race km or 46000 road km, it's likely to need looking at in one way or another. If it fails, it's going to be expensive, and your options are [approx] £500~600 for a rebuild, £xxx on an unknown used item, or close to £1200 for a new one from Honda. Any used crank, in my opinion, should be pulled apart, measured, and have at least the mains done, because you will never know it's true history unless you bought it new. We've seen people got through several second-hand cranks in a season before. A complete false economy.

£25 to pull one apart and have it mic'd is a bargain, even if I do say so myself! If it were costed by time, it would be many times that amount, and can still potentially save you thousands if you have a very bad failure.

NSRs are at an age now where cranks are becoming a definite issue. MC16 and MC18 cranks are no longer available new from Honda, and I am reliably informed that there are only a small number of MC21/28 cranks left worldwide on the Honda system.
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Andy.
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What would anyone consider the life span of the conrod to be ? It would be a shame to replace all the bearings and a rod failed a few months later .
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NSR300

Never seen an NSR conrod break. Not saying it can't, or that it won't happen, but have never seen it. As long as it's within spec, and the bearing/thrust washer surfaces are good, then they have always been fine to reuse.

I am sure you will already appreciate, Neal, these things cannot be measure by mileage. We take nothing for granted. Everything, and I mean everything, is measured with the micrometer.

Our cranks circulating the IOM in HRC RS250s have had rods reused multiple times. We've never had a failure.
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Andy.
NSR-WORLD.COM

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