Indeed, if you have a good running engine you won't really notice a diff. I did it to a mate of mine's GSXR750, and he didnt notice anything power wise, only that it went from 14k's per liter to 17k's per liter.

My engine had 76000k's on the clock and was running like s**t when i bought it. 4 valves were almost beyond repair, and the rest was pretty bad. So, then it does make quite a diff.

CMSMJ1 wrote:good arrows Rhory..
Methinks it would be good if you lived around the corner so we could sup tea and compare tactics!

yes methinkthatalso...as you and i tend to think of the same things around the same times

to be honest i'm not feeling the love for this at the minute,some say nothing changes some say it'll depend on the state of the motor in question

will i or won't i .....

do a compression test.. if its ok, leave it .. as there wont be any tengible benefit to lapping the valves in if they ar already sealing ok.

you cant really clean the ports up with the valves in, and again its unlikely to make a very noticeable difference if you just intend cleaning up the casting impierfections... leave it till it needs it.

proper 3 angle valve seats would make a difference as they drastically improve flow at low lift, but its not a DIY job.

I have the heads off my spare motor on my workbench and have already started to remove the valves. I am wondering about the valve stem seals in the head - do I pull them out too? The motor is not healtyto sart with - I thnk the botom end is kaput and so I will eventually striup it right down just to see what goes on in there. If I get minted then would love to build a big bore out of it....but money would be the killer..

I have an air dremel and lots of wet/dry so this will be a chilled out kind of affair.

have seen the old forum has some good pics from Mike Norman and also from....hmm..one of our Danish friends??.hmm cannot recall his name.

Why not replace valvestem seals? Cost nothing and with any 10+yr old bike the stock seals don't seal as wel as they used to. So you get small amounts of oil in the combustion chamber and on your valves... which you dont want

CMSMJ1 wrote:The motor is not healtyto sart with - I thnk the botom end is kaput and so I will eventually striup it right down just to see what goes on in there. If I get minted then would love to build a big bore out of it.....

yes yes yes i'd love to do a 433cc motor for the road but i'd want to get a kaput motor to start with (nothing overly mullered but) so when i have it built back up i have something to be very proud of....maybe you and i could work together if we decide to do it ....


but i'm not feeling the love for this diy head porting as not many are saying there's much benefit to be had from doing it....

maybe i'll just wait to get my mullered stock motor before i 433cc it and do the heads etc then.....


best look out for a stagged motor then lol,mark ,you don't know of any going cheap do ya ?

i was also thinking of porting as a little winter project but i heard if you remove too much material from the ports then you slow the air flow and reduce the amount that gets into the cylinders and the bike makes less power!
Buy a book called four stroke performance tuning by A Graham Bell - it goes into great explanation on this subject and is very handy if you have trouble sleeping! i was thinking of just smoothing the casting imperfections which i wouldn't expect to create much of a power increase

I remember reading once that it's an idea not to have the inlet ports totally polished but better to have a slight roughness to them.

Druid

I remember reading once that it's an idea not to have the inlet ports totally polished but better to have a slight roughness to them.

+1, I believe it's to encourage the fuel-air mixture to swirl and combine better.

I played around with Mini cyclinder heads in my younger years, and I have to say that without a flowbench there's little you can do to improve the standard set-up. Changing exhaust manifolds, air filters and camshafts on the other hand does a lot for extra power, as does replacing standard valves/seats for three angle ones (as mentioned earlier).

fastdruid wrote:I remember reading once that it's an idea not to have the inlet ports totally polished but better to have a slight roughness to them.

Druid

true.

you can polish exhaust ports and combustion chambers to slow carbon build up, but polishing the combustion chamber also enlarges it a tad, lowering compression ratio.