After working on one cylinder head for a while, I got nervous about taking a Dremel to the valve seat. I did a lot of reading but could find very little info on hand radiusing valve seats. From talking to my machinist, the NC30 valves are just too small (both in diameter and valve stem) to be able to use a seat cutting machine. This doesn't leave many options other than detailed work by hand but without a flow bench to quantify the changes I was making, it was just shooting in the dark.

This led me to make the decision to shelf the head porting for the time being and concentrate on dialling in the HRC cam grinds that I have had sitting on the shelf for the past 2 years. I knew that the piston/valve clearance would be tight with skimmed heads if I was to dial the cams to 105 lobe centres as specified so used a spare set of unskimmed RVF heads.

Dialling in the HRC cams

I set the valve clearances to be the largest specified by Honda which was the same spec that I used on my #1 build:

Inlet: 0.18
Exhaust: 0.27

Then started dialling the cams in to 105 lobe centres. I didn't know a whole lot about these cams other than they were the HRC grind which I assumed that meant the F3 kit cam spec. There was a Tony Scott spec sheet so I was really keen to find out how my measurements would compare:


Slotted camshafts


HRC grind from Colt Cams

The spec that I got from the cams was:

Valve Lift IN (mm) - 8.0mm
Valve Lift EX (mm) - 7.5mm

IN Valve open (Deg BTDC) - 18
IN Valve closes (Deg - ABDC) - 49
EX Valve open (Deg BBDC) - 43
Ex Valve close (DEG ATDC) - 13

Duration Inlet - 247
Duration Exhaust - 236

*All measurements taken at 1mm lift


The measured max lift matched that specified in the F3-TT manual and the opening degrees pretty much matches the Tony Scott spec sheet. However, TS quotes a lower max lift and a longer duration. Without knowing how he measured this (0.2mm lift, 1mm lift etc.) it is impossible to use it for ref.

I pretty much landed exactly where I wanted to (105.5 inlets, 105 exhausts) but needed to check the piston/valve clearance. I have not found a value for this on a stock motor but Colt Cams recommended a minimum of 1.2mm. I pulled the heads and plasticised up the piston tops. Then reinstalled the heads and cams, turned the engine over a couple of times and the took it all apart again! It is a lot of hoops to jump through but the only way to be sure.





The exhausts were a little tighter than the inlets but both well within the minimum (inlets: 2.5mm, exhausts: 1.8mm). In theory, the 0.5mm head skim would still be within the minimum but cutting it pretty close.

With the cams dialled in, I bolted the engine back into the frame and re-fitted the exhaust, loom and radiators. This gave me the opportunity to fit the thicker header brackets and also hammer a small dent in the LHS front header pipe to get more clearance between the oil filter and the header.

I'm shooting for a test day at Manfeild on either the 17th or 24th April to run the engine in and tweak the carb setup for the new cams. I'll try both the FCR's and the HRC setup back to back but really that'll require more dyno time to really dial those in.

wonder if the seats are cut back more in the rvf heads ? thats safe as

Could be? The heads aren't skimmed though so I do have a bit more of a margin

on my heads , i only took .3 off my engine( brothers) and could not even turn over! to be fair because of that i did not bother seeing what the timing was so only worryed abould pison to valve clearance , next one i will cheak

so whats going on with the bike ?

Well.... I went to the test day on the 17th April to run the bike in and entered round 1 of the Winter Series. However, I could not get the bike to run on 4 cylinders. I tried everything and it would just not fire on #3. Stripped the head at the track and thought a had a bent valve so called it a day and cancelled my entry

Work got busy so it took me a while to get back to it, but I checked the port and the valves were sealing just fine. Scratched my head a bit and then I clocked the issue... I hadn't blocked the vacuum take off for the fuel tap on the #3 cyl (I'm running a constant flow tap). It is sort of hidden behind the water pipe so I missed it at the track and these are replacement heads. Cool thing is it is a 1 min fix so the bike is now completely sorted. Just need to book another day off to run it in and enter again!

Been a while since an update. Got distracted rebuilding Vespas for a few months but am now back onto the nc30:

http://hondanc30.blogspot.co.nz/2016/06 ... ld-25.html

Finally entered a race! Mixed weekend but was pretty good to be back out.

Full write-up:
http://hondanc30.blogspot.co.nz/2016_12_01_archive.html

Short version:
Qualified: 6th
Race 1: 8th
Race 2: Crashed

Race 1 video:
https://vimeo.com/196065759

Once you have the cdi issue fixed I'd love to know what you think of the engine now you have the hrc spec cams in. Re the compression the hrc manual lists it at 11.5 : 1 with the F3 pistons so think you are spot on

Interesting! I really should buy that manual from you. I still only have the non-tranalsted version

Thanks
Luke