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Valve seat inserts on a 1700 Supersprint Big valve head


orangepeel61

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Just taken the head off in order to fit new valve seat inserts for an unleaded conversion however the engineer said that there isn’t enough “meat” on the gas flowed head to fit inserts, the risk is that they would cut into the water jacket and he wasn’t prepared to do it.

Trawling through all the posts on here I have found references to this being the case but the only solutions given are to replace the head.

The engineer said that it wasn’t a problem and he could harden the existing seats with a heat treatment with what I think was a Potassium acetate (?) he was adamant that it would do a reasonable job and says he’s been doing it for years.

I’m having trouble finding any information about this process on the internet, can’t help feeling that if it works then lots of people would be talking about it.

Can anyone throw any light on this!

For any cynics  (I would be one) no, he’s not trying to rip me off with an “expensive” process, quite the opposite in fact, he genuinely seemed to be trying to save me some money.

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Quick answer is that he is probably referring to a bog standard heat treatment (stick them in an oven, heat them up with a flame etc.) followed by a quench in a potassium-based (usually nitrate) salt bath. Quite an old technique for heat treating of steels.

I've never heard of it being used for valve seats, mind.

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If it's a genuine and unmodified Supersprint head there really should be no problem fitting inserts (exhaust only, inlets are not necessary) if using a competent company.

If the valves are larger than standard, it can be risky, but the danger isn't of breaking into the waterways, it's of cracking the head between the inlet and exhaust valve which will then render the head as scrap. I used to produce big valve heads with unleaded inserts, but this was always done to a head that had standard valve sizes which were then opened out for larger valves.

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I’m pretty confident that the head is unmodified, the exhaust valves are 41mm like elie boone’s. The guy I was talking to was an old guy whose been doing motor engineering for years, I don’t doubt his ability (that’s why I went to him) but it’s looking like he hasn’t had much experience of the Supersprint head.

Still curious as to what he was on about though.

Thanks all for you help

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I have a Supersprint head and it has hardened inserts. It runs standard exhaust valves and big inlets. The work was done at  F J Payne & Sons in Eynesham. They came recommended by my garagiste (Bernard Saunders in Bourton-on-the-Water) and know their stuff and their pricing looks reasonable (no one is ever cheap are they!).

Personally, I'd be nervous of what your guy says. Don't know if he's right or wrong but getting a second opinion from Paynes (is that anywhere near you?) might be useful. Give them a bell?

Good luck!

Andy

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Andy,

I was nervous so I've just been to F J Payne & Sons, they seem friendly and helpful, they said they'd have no problems putting inserts in (they'd also never heard of heat treating cast iron!)

So I've left the head with them..... we'll see!

Thanks for the info

Neil.

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Pleasure. My man who recommends them uses them for engineering work. He has or looks after a number of ex-works Honda bikes (including their first TT winner) so I tend to trust his judgement Neil! When I went into their workshop recently (they replaced my inlet valve guides a few weeks back), there was some very tasty vintage machinery being worked on so they're trusted by others too.

Fingers crossed it all works out OK - I'm sure it will.

Andy

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