Nc23 engine refurb

[drifterwannab]

Hi all,

Need to strip engine casing to refurb my gear box,

while iam in there should i change the piston rings and valve stem seals

if so, best place to get them from?

Any thing else i should do while got it apart

[greggo]

depends on how much dosh you wanna spend and how technical you want to get. But trying to stay practical for a garage mechanic who knows a bit:

1. I would at the least measure the piston to bore clearance and try to match each piston to cylinder for the 'best clearance'. I'd even consider looking for second handies that would be a better match and get you the ideal clearance.

2. Replace the rings

3. Hone the cylinders

4. Balance pistons (and rods) if you can be faggered. Put the pistons on a very accurate scale. Remove the TINIEST amount of material from the underside until they all weigh the same. (Same with the rods - but i'm told to put them on two scales - one at each end to balance them). This reduces unbalanced loads on the crank decreasing wear.

5. Valve guides I wouldn't do unless there is evidence something is wearing (look for blow by) - they tend to last unless abused. Inspect the valves for undue wear at the edges (look for knife edging and replace)

6. Lap the valves. Put some valve grinding paste on each and then work them until there is a good seal. Will require re-shimming

7. New bearings throughout seeing as you have the crank cases split, and they aren't too expensive. If you aren't confident have someone who is do the measuring.

You could do all, none, or more. Just depends on what you want from it. None of it will lead to more power, but you'll get a little reduced wear and increased efficiency and a big stiffy when you swing your leg over the bike you built.

[drifterwannab]

excellent thanks! never thought about balancing the pistons - very interesting

I saw Drew70 fitted RVF pistons, is there many people done this?

[drew70]

Dont do it ive blew up a few motors running rvf pistons
Unless it was the 16,000 rpm that done it

[greggo]

My race bike has the RVF pistons in it.

No problems yet...

[drifterwannab]

Dont do it ive blew up a few motors running rvf pistons
Unless it was the 16,000 rpm that done it

nasty! Gutted for you!

What is the reason for fitting the rvf pistons? Does it give high comp ratios, or are they lighter

Not planning on uping the rev limiter, so is it just due to over reving you have had a problem?

[greggo]

The RVF pistons are higher crowned than the standard CBR ones with identical bore sizing, wrist pin etc. So you get a slightly higher compression ratio without having to fiddle with the gear driven cams and deck height, which can get a bit serious. Plus the compression still allows the use of standard pump gas, it's not high enough to cause pre detonation or any of that nasty stuff.

Dunno if there is any price difference. May be the RVF ones are more available and cheaper? (I feckin doubt it!)

As to blowing up, I reckon he may have over revved, which has popped up in another thread recently. The engines canne take it cap'n!

[drew70]

One blow up was down to over reving on the down change
The other was when i was taking it a bit easy running in a fresh rebuilt motor i missed a gear and it free revved to the max .
Funny though both blow ups have happened on cyl one.
So now running std pistons and only .02 sec of my fastest lap at my fave track when i used rvf ones
It loses a little bit puling out the corners but at top end there aint much in it