Topic: old valves worn head

[carsholduptraffic]

when putting old valves back in, should i take the valve stems back to shiny metal (ie take off the darl discolouration)? i'm inclined not to, as the whole lot is worn and really needs new guides etc, but i have another head that i'd rather spend the $$$ on, and i just gotta get this thing off the dining table. desperate times call for desparate measures.
any tips on sourcing new valves, guides, springs etc for the cb750?
the head (mk2) i have is ported nicely (relative to the 70's cycleworld? article and pics of mjreck's work) but has no valve seals on the exhaust guides. was destined for a drag bike in the 80's allegedlly.
i'm thinking bigger valves, with nice seat job, guides as required, good springs, light but tough retainers and have a close look at the cam tower bearing setup. nothing too wild, as i dont want camchain dramas, and it must be bulletproof for riding across this vast brown land.

[MRieck]

Kibblewhite makes 32mm and 33.5 intakes as well as 28mm and 28.5mm exhaust valves. They also make guides, springs and titanium retainers. It sounds like you have an older head as the exhaust guides don't have seals. They should be replaced and if doing the exhaust guides you might as well do the intakes guides too. The work you are talking about, oversize valves etc, sounds great and will make a huge difference. If you need help getting parts let me know as I can get Kibblewhite parts,heavy duty cam chains etc at a very good prices.
  Mike

[carsholduptraffic]

mjreck, can you give me a ballpark figuire for the bits needed for new vavles, springs and guides?   the ported head i have has new guides (sealess on ex) and the seats look fresh. can i just get the exhuast guides replaced, or is guide replacement a one out all out job?
i expect valve spring holders would be reused, new springs & new retainers (how $$$ are titainium?) and to ream guides to suit valves. i;m after more grunt fron the 836, not top end. but top end is nice. is 80hp at the wheel realistic?
motor must be able do destroy a rear tire on the sojurn to phillip island (i cant help myself in the trackside campground), and make it back after (the hungover monday morning tire lever dance). and then start everyday forever after.
and i final question to ponder.........is a yammy trx850 a worthy replacement for a daily bike, if i go balls out and turn the cb into a racer?

[MRieck]

I'll get those for you tomorrow sir. Sorry for the delay.

[MRieck]

Got them but I have to go out. Will send you an email tomorrow.  Mike

[carsholduptraffic]

thanks for the info mate! i just wish the kibblewhite site was up.
i noticed that you have a 5mm valve conversion on your million dollar bike....a good thing for a streeter? i'm on the other side of the planet, and finding bits is tricky (i'll be contacting you shortly terry), but i have found a local machinist that has enough wrinkles to know honda fours and the rebuild will be recomencing shortly.
blokes such as yourself are a godsend to us amateur engine builders.........thanks.
p.s. how critical is piston to bore clearance? (100.000km on them, wiseco, done hone & rings- can i expect success?)

[Terry in Australia]

I'm here for ya mate! Cheers, Terry.

[MRieck]

thanks for the info mate! i just wish the kibblewhite site was up.
i noticed that you have a 5mm valve conversion on your million dollar bike....a good thing for a streeter? i'm on the other side of the planet, and finding bits is tricky (i'll be contacting you shortly terry), but i have found a local machinist that has enough wrinkles to know honda fours and the rebuild will be recomencing shortly.
blokes such as yourself are a godsend to us amateur engine builders.........thanks.
p.s. how critical is piston to bore clearance? (100.000km on them, wiseco, done hone & rings- can i expect success?)

Piston to wall clearance is important. Too loose and you lose power. Really to loose and you get piston rocking/slap which totally blows away ring seal. .0018 to .002" works well for clearance. Perform a leak down test to assess the pistons- 100,000KM seems like alot of miles. Yes the 5mm kit works great but it is pricey.....but did I mention that it does work great.

[carsholduptraffic]

i haven't got the measuring stick onto the pistons and barrels yet, but just by eye and feel, i think the piston-bore clearence is a lot more than .0018". there is a definite rock to the piston in the bores. i had the rings and barrels already on when i had this rethink, so it's teardown time again, and do it again, this time with feeling!
the pistons look good, and i have a spare block, so my question is.......as worn pistons won't be truely round any more, pending further measurements, is boring a fresh block to suit old pistons the done thing? or am i just pissing my $$$ away, and should just get new pistons?
i'm sure i will eventually work it out for myself, but trial and error gets expensive!!!!
and thanks to terry for giving me something to think about! i do admire the t-rex hondas, even if they do sail close to the rules in post classic! i rekon i'll go that way.
now.........to find some fancy measuring sticks.............!

[Terry in Australia]

G'Day Nick, well unless your pistons have obvious signs of major wear, I say bore another block and chuck in some new rings! Did I mention that I've got my own boring bar mate? $25.00 per hole, or 2 litres of Jack Daniels plus shipping! Cheers, Terry.