Hi all,
I've got my 91 NC30 stripped for a tidy up prior to Summer.
Plastics are away for repairs and paint, wheels off for powder coating, new rear shock on the way, various carb bits and fork internals are coming from Rick Oliver etc etc.
Now, while I've got the engine out I'll check the valve clearances but, seeing as I'm going to be waiting weeks for various bits I was wondering if there's anything else I can be doing.
I was thinking I could polish the ports a bit and knife edge the splitter, maybe lap the valves but I'd like some advice before jumping in.
The bike is a toy for road use and track days, not to race, so power gains are welcome but not all important.
Cosmetically the bike was tatty when I got it but it has been well serviced and now has 17,000 kms on the clock so internally the engine shouldn't be in bad nick (I hope).
I'd have to order head gaskets in but I've got plenty of time. I've got plenty of tools and we have a fairly advanced machine shop at work with CNC this, that and the other. Skim a thou off the heads? Probably not but I've no idea what affect any of this has on a VFR so I'd really appreciate any advice and suggestions on what useful things I can be doing while the motor is out.

My 35 has skimmed heads, i dont know how much but engine has had a lot of other work done aswell. It cant be a bad thing

I had the same when I biult my race bike.

Lap the valves in and clean the piston tops
flat out the casting marks in the ports
give it a bloody good clean
remove the backlash gears - if you fancy some more noise!
set the clearances perfect (as per the HRC book)
clean the oil strainer gauze

I wouldn't mess with it. These motors are bulletproof if you take care of them.

Polish the exhaust ports but not the intakes, the slight extra turbulence of the casting helps with fuel atomisation.. If you take the heads off, may as well put new rings in and replace the valve stem seals. I got a full gasket set including them.. Youl also have to rehone the bores for the rings, get this done professionally... You could also check all bearings and clearances while its open

sorry for the silly question but may i ask what 'lap the valves' is?

I'm assuming you know what a valve and valve seat is here but, if you do, you'll understand that the valve has to 'seat' properly to be fully sealed. Lapping is using a tool (lapping stick) to rotate the valve in it's seat with grinding paste in between. This matches one surface to the other. For badly fitting valves/seats a cutting tool is sometimes used first. Do a search on youtube for video results that will better explain the process.

Hmm. Some do's and some don'ts there.
Reliability isn't a huge issue as it's not a regular ride/get me to and from work bike. Obviously I don't want to do anything to greatly compromise that legendary reliability though.
The way I see it, lapping the valves and cleaning up the ports a bit can’t be a bad thing. As for honing the bores and replacing the rings, there’s no-one locally has the gear to do it (too small an engine) so I’d have to send the heads away. Id rather spend the money on the dyno to be honest. With 17,000ks on the clock I’m hoping that all the seals, rings and the bores are ok. I’ll know more when the heads are off. I will check everything though.
I was thinking more along the lines of the things CMS suggested which I’ve done on other bikes and am confident of doing myself without causing damage. This kind of thing can only help the engine breath better and should improve reliability rather than degrade it.
CMS, I’ve got a HRC manual somewhere that I downloaded but haven’t really looked at yet. I’d have to see if I can find those settings you mentioned.
Mexican, I mentioned not touching the intake ports to a couple of local guys, including Fred Merkel, the ex AMA world superbike champ, and most didn’t agree. I was told that if fuel in the intakes isn’t fully atomised by the carbs, the carbs aren’t right and that disruption of the intake flow causes fuel droplets to combine and gives an uneven spread of fuel/air mixture through the chamber. I was advised to polish both intake and outlet ports as close to a mirror finish as time and patience would allow.
As for increasing compression I know that this is often achieved through the pistons rather than skimming the head.
Anyone got any solid advice or experience on this?
Anyone got any advice on opening the ports a tad? I think there are HRC guides for this but I probably shouldn’t go that far. It might give some pointers though.
Are there significant gains to be had removing the backlash gears? If it’s only half a pony I’d rather do without the noise.

Cheers,

About what I expected Cammo. Replacing the pistons was never something I'd consider as, if I could find 'em, I'd be better of spending my money elsewhere, like in the pub.
To be perfectly honest the best way for me to make gains on lap times is to do more laps.
Still, if I could improve things with a bit of hard labour, that's all good.
So, clean the ports up but no more than that.
I've heard a few NC's with the quietening gears out and while some were pretty noisy (a bit like my mate's 749) some were fairly quiet. When asked why I'd get a knowing look and comments along the lines of "it's all in't shims lad." At this point I'd have been wise to have applied liberal amounts of alcohol and to listen attentively, but I didn't.
I'm guessing here but, if for example you skim 0.2mm off the head, do you shim each cam carrier the same amount or does this need to be measured for each cam wheel?
Is this even worth doing if I leave the backlash gears in? If careful shimming keeps the noise down a bit I’d be keen to give it a go.
Again, it's not a race bike so half a horse isn't really worth it. That said, most of the tinkering I do, I do because I like to tinker.