I have a rear mc21 cylinder head here, which has been involved in a slight small end bearing/piston crown mating session. It has a few grooves and dinks, anywhere reputable in the uk that can fix the bugger for me?

Thanks
Paul
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More **** two strokes than you can shake a **** stick at.

Derek Huxley might be your best bet, done some cylinder repairs for me before, no problem, I think he is at Ellesmere Port, so not a million miles from you, sadly i cant find his no: or address, but i think Roy has used him before so he might have his no:.
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Proud Father of , 05 ktm 400exc supermoto 2018 honda crf rx supermoto

I'll give him a shot, used him in the past.

Thanks Les!
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More **** two strokes than you can shake a **** stick at.

Yes, Derek's good. Got my heads done on time when he said he would. Turned them around pretty fast.
I had the volumes set, reprofiled and had detonation rings fitted. One of the heads had a fair amount of damage where a bit of broken ring had gouged it.

I went over to his place to drop off and pick up my stuff. He likes you to call him first if you're going over.
He's quite busy with BSB around those weekends too.

Does it pay, to have standard heads repaired instead of buying new ones ?
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Poul
"If Life Gets Boring, Risk It!"
MC21SE, KISS box
MC21SP, HRC box, racing loom

pbekkerh wrote:Does it pay, to have standard heads repaired instead of buying new ones ?

Yer pays yer money and yer makes yer choice!

Seriously though, it's a well known and proven practice to have heads repaired and modified in this way.

Is it an economically viable option to repair ?
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Poul
"If Life Gets Boring, Risk It!"
MC21SE, KISS box
MC21SP, HRC box, racing loom

I think Poul's referring to NSR heads Roy, not RS heads.

If someone is set up to machine NSR heads, then it's worth repairing them, but it's not as simple as doing RS heads. On the RS a "plug" (not spark plug!) is easily screwed into the central hole, to allow them to be turned in a lathe. As the NSR doesn't have centre mounted spark plugs, a jig needs to be made to hold them.
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Andy.
NSR-WORLD.COM

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Andy wrote:I think Poul's referring to NSR heads Roy, not RS heads.
.

Thats correct. Are there anybody doing NSR heads ?
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Poul
"If Life Gets Boring, Risk It!"
MC21SE, KISS box
MC21SP, HRC box, racing loom

I had a jig for MC21 top heads, but I can't find it. It's something I'd like to do again at some point.

There's no-one I know of that's set up commercially to re-cut MC21/28 heads.
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Andy.
NSR-WORLD.COM

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If I was using unleaded and tuning my motor I would definetly have this mod done .

I'm not a machinist/turner but a faceplate can be used to hold the NSR head on a lathe.
I think that would keep the cost of machining down at a machine shop.
Of course, if a jig has to be made. Then you would expect to pay more.
You would of course be paying for the time it takes to set up the head on the faceplate also.

It was £50 per head at Derek Huxleys' for what I had done. I think that's quite reasonable. He didn't charge extra for the damaged head, although it must have been at least slightly more work.

We'll have to find out what he charges to repair Pauls' damaged head.

I don't know what a new head would cost but I'd bet it will be more than the repair cost.

Just checked. £151.13 plus VAT for a MC21 rear head. Stocks are very low and it may take 3 weeks to arrive.

As StephenRC45 pointed out to me a while back, the mating faces on the top of the head (the seats the flanged nuts mate against) cannot be guaranteed to be true, so there's no way to be sure the head sits square. These faces would need to be machined first, then the head set up on the faceplate or jig.

I expect there not to be a lot in it for a one-off head repair, as an NSR head will most likely effectively need to be machined twice. Once to get it to sit square, and then again for the combustion chamber, although I expect it will still be cheaper than buying a new head.

Ideally someone wants to do 10 heads to make the setup worthwhile and bring the price down. If a machine shop were to be up for it (and give a price and service), then while not getting a mass of business, could be recommended as the "preferred supplier" on NSR-WORLD if they wanted. We'd then push any future business their way.

However, as with many things, it's all very easy when you say it fast!
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Andy.
NSR-WORLD.COM

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My mate machined the sides of my 21 heads.
Took a small amount off of the bulges where the head studs pass through. Got enough of a round surface centred on the combustion chamber to allow the head to be held in his large chuck.

At least, that's what I think he did! I'll have to ask him again! You can see the machined areas in the pictures.

Yeah, that's OK, if you don't mind overt machining on the outside of the castings. Not everyone's going to be happy with that though.
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Andy.
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