NC29 Race engine project

[greggo]

Right on. Only 70-100 of the local pesos, and same day turn around, to skim the head by .5mm. I'm dropping that baby in tomorrow arvo.

Is there anymore needs to be done to the gear drive to accomodate this?

[dannc29]

yes, otherwise your engine won't bolt together. its alittle time consuming and teases the brain alittle. im assuming the nc23 head is the same as the nc29 head? except for port size or something like that. there's alot to account for.

first you should bolt your engine together and measure piston to valve clearance for intake and exhaust.

from my understanding youv'e made your cams adjustable? because if you havn't i wouldn't do this mod as it'll put the cam timing out.

going off the the piston to valve clearance specs will tell you how much room you have to play with. make sure you measure every valve to piston clearance as there's variable in each piston and valve seat height. in my engine i had .2mm from my smallest clearance to my largest clearance.

i spoke to harley from rb ages ago, he took some rvf pistons out of his engine which he had running at 1.2mm clearance on the exhaust. you could see the valve inprint in the carbon of the pistons. i don't know if this was over reved on downshift or just normal.

i ran my clearence at 1.29mm exhaust and .7 intake without an issue most of this year. i havn't pulled anything apart to see whats going on inside but there are zxr's running tighter clearances, which are chain driven so really the cbr's gear driven should be able to run a tighter clearance.

anyway, just say you had the room to take off .5mm. you grind .5mm off the underside of the drive gear where it bolts onto the head. this moves both gears down so the cams will mesh with the top gear correctly. now your left with the bottom gear meshing to tightly with the crank.
you need to move this gear sideways. approx 1cm for .5mm off the head. so you cut the drive gear bracket in half then reweld it in the correct position that gives you the right backlash. that is the most tricky and time consuming part.

i can go into more detail but thats the jist of it. should boost your compression upto about 14:1 so only ever use 98 ron fuel.

[dannc29]

there's also piston to head clearance you need to worry about. i could measure it exactly but i had over .7mm so it was safe everywhere. if the nc23 has a different combustion chamber shape you'll need to measure this before you shave the head.
also dial in your adjustable cams first before you do anything. cam timing will effect piston to valve clearance. try 103 intake, 105 exhaust loab centers. power wont really kick in till about 9-10k rpm but won't drop off at all before redline. if you can't keep the revs that high try 101 IN -105 EX loab centers, power kicks in earlier but starts to fall away at around 14k-14.5k rpm. personally i prefer the 103-105.

[dannc29]

also, while you have you engine apart. look where the head gasket meets the barrel. on the head gasket you should see 4 valve cut aways per cylinder. you'll notice that the block hasn't got them cut away. chamfer down to barrel to match the head gasket don't take too much off as it will subtract from you compression ratio. make sure you also chamfer the combustion chamber around where the valves protrude. and any sharp edges.

[greggo]

Thanks for the write up Dan. A lot of tools needed that i don't have to get that done. I would say I'll shelve the skimming and jut play with valve timing. Although that depends on the time i have when I get back from holiday.

My finished dash

[greggo]

Got my straightened bits and bobs back today, so rebuilt a nice fresh set of forks.
120mm Air gap
124mm Spacer
2 Washers (at either end of the spring)
0.85 kg Front Race tech springs
Racetech emulators set at 2.5/5 turns
10 Wgt oil
New bushes and seals.
Noice. I like that set up.

All that adds up to 5mm of preload on the springs at full extension when assembled.

Nothing much else will happen now for 4 weeks while I go on holidays. When I get back the whole thing will go together in short order as I want it finished by the end of Jan. Effectively 2 weekends of building.

[chrisja2]

Sounding good Greggo, really liking the digi dash. Tasty set up on the forks too. Are the emulators there because the forks are the early spec? Im just pricing upgrading my forks, spring, emulators etc off GF.
Did you win the proflex shock?

Chris.

[greggo]

Yeah, I use the emulators as I have the early forks with no adjustment. Yep, I won the proflex for 112gbp, hopefully that's a good price! Well spotted, thanks Chris!

Managed to sort some reasonable headers and engine bolts for my number 2 bike too!

[greggo]

Sit down to reassemble my engine now everything is in one place and I have all the aprts.

Figure I would start by putting the pistons onto their rods and sliding them into the bores.

Well my rebuild finished right there as the MORON from NZ has sent me the wrong piston rings. FFS I don't actually have a lot of time to get the bike on the track and run in along with everything else.

RAAARRRRRRRRGGGGGHHHHHHFUCKENURRRRRRRRRRRRRRRRRRRRRRRFGZHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH

[racesupplies]

We went down the light crank route,it didnt really acheive what we wanted from the engine.It sounds good blipping the throttle warming up,but thats about the best of it.400s are all about getting the best start,and corner speed,a light crank does nothing for either of those.I agree with yeurman,it doesnt get off the line with as well with less inertia.Knife edged webs are a different thing.I have seen a crank spinning at half the revs we go to,its scary.That cased in a confined space mixed with oil vapour offers enough resistance to absorb BHP. Knife edgeing the bob weights,and deburring/polishing the rest is a good idea,so is a really good dynamic balance by someone that has a good track record with cranks that spin to our revs.Out of balace forces sap power as well.Compression is the easiest route to more power on a 29,unless you skim you wont get enough to go far past 70.Its a pain to sort the gears,but probably take about as much time and money as you have spent on your crank.Ive got 3 motors in different specs,the fastest has got a bog standard crank.The slowest at the moment is the most expensive knife edged one we used at the Manx this year,It is visibly slower off the line.If you want to see the quick one go have a look on youtube.Thundersports GB Rockingham 09 Junior powerbikes. If you want a close box I a friend of mine has 4 available,but they are really expensive.We tried one last year and I will be getting another from him in the spring,makes a real difference,but a bit of a luxury.Hope that helps,have a look at that vid.Cheers Carl.