Inlet valves

[pauliexjr]

Hi All, just in the throes of rebuilding the head and after de-coking the valves the tapers on the stems of my inlets are quite badly pitted. I've looked for new ones but they seem like rocking horse poo and the few I have found are incredibly expensive. I was thinking of taking them and the exhausts to my local machine shop and getting them turned down as I'm looking at a mild gas-flow on the head anyway. Any thoughts or recommendations?

[Bryanj]

YOU CAN NOT re-machine the valve surfaces on the valve as they are not fully hardened, Which model is it as Dave Silver has most of them?

[davepainter]

Hi a firm called jts motorcycles are currently advertising exhuast valves on e-bay at

[pauliexjr]

YOU CAN NOT re-machine the valve surfaces on the valve as they are not fully hardened, Which model is it as Dave Silver has most of them?

It's a CB750 F2 sohc. I've looked on Dave Silver and can't find them, CMSNL want 77 Euros a pop! The actual compression-side surfaces are fine, it's the area behind the seat leading up to the stem that's pitted, and from my experience of gas-flowing Mini engines turning the valves down to a 'penny on a stick' is part and parcel of getting a better gas flow. Are you saying that can't/shouldn't be done?

[Bryanj]

NO that definately should not be done if you want a decent life and undamged engine! Dont forget these motors already rev markedley higher than a mini.

If you go to our sister site in the US (SOHC4.net) and look up dynoman he does valves with smaller stems (along with guides to fit) and i bekieve standard ones as well. Also worth looking up Mike Riek as well as he gas flows the Honda fours incredibly well and has a wealth of knowledge as to what works and what doesnt

Have you checked the exhaust guides as the F2 is notorious for wearing them out very quickly

[UK Pete]

Here you go paul,  http://www.ebay.co.uk/itm/150406958929 he does all sorts of goodies for the F2
and silvers stocks the standard valve guides as well, i bought all my stuff at dynomans then i discovered this guy at half the price   (ARSE!
how badly pitted are the lower stems, it might be ok to still use them, can you post a picture
Pete

[UKROBK7]

I can recommend Cyclex as well.  Just watch out for the customs duties!  I had to pay an extra

[K2-K6]

As the others are saying the F2 is probably a good deal more critical than a Mini motor in this area and although four-stroke principles are related, you are unlikely to get two motors more different than these.

I understand that a good part of the flow in the F2 head is affected by the dimensions of the valve seat angles and without being particular in this area other stuff can't produce any really measured improvement from a basically std motor.

Standard mini heads are by comparison very poor for performance so gain is easy as the head is a significant restriction.

The F2 motor went up only by about 5bhp from previous models with all that Honda could do to it (valve size, rev increase, cam lift and timing, carb changes)  I'd seriously doubt that any small changes could make any gain on that but more likely to loose some if not at least meeting a good production spec.

[pauliexjr]

Here you go paul,  http://www.ebay.co.uk/itm/150406958929

This guy is the dogs wotsits! Less than 12 hours to reply to my enquiry 'will they fit stock valve guides' and a price of around

[UK Pete]

All the good guys seem to be in the USA,
As for the frame mod there are a couple of options , the best one is the gorden frame kit found on the other sohc forum, but there is also my own version of the frame mod  which is a real cheap way of doing it for less than