Engine rebuild

[Wicky]

How to select a cam profile > http://www.classicinlines.com/SelectCam.asp#

For car engines but generally the same principles apply

[tony.mon]

I just decided that 1mm lift increase was my target, and that meant grinding 1mm off the base circle.
(actually, about 1.2mm)
Then I asked for the dwell to be made as much as possible within what was left within the new lobe area, with a reasonable ramp.

Trouble is, I didn't practise what I preach, and made several changes at once, so I can't isolate out what if any difference the additional lift and dwell gave me. I put high comp pistons in at the same time; and gasflowed the heads.
I used the std cam positions, but may have a play at some time with advancing the inlet slightly, as I think that would improve breathing.
This is based purely on the fact that the profiles of most aftermarket ones are more advanced, as far as I recall. I published some comparison data on here somewhere re different cam profiles, lobe centres, lift and duration, but this doesn't give nay info re ramp angles and the actual profile.
Although the lower lobe base is less than perfect in terms of the thickness of shim required (thicker shim=heavier shim), it shouldn't make too much of a problem, as valve bounce with the std springs isn't an issue with a normal rev limit.

[lloydie]

thanks for that tony
is it posable to have the standard cam's re-profiled to the stage 1 moriwaki's ?

[tony.mon]

thanks for that tony
is it posable to have the standard cam's re-profiled to the stage 1 moriwaki's ?

Reprofiling can only be done where all of the new profile falls within the metal of the old cams.
Lowering the base circle is a way of cheating, but isn't perfect, especially if the cams have been surface-hardened or plated. Too low and you lose efficiency, and have wasted your money- you'll have wasted a lot more if the cam is too weak and snaps.



I would have thought that you'd have to go too low on the base circle to make that possible, but it may be ok.
Trouble is you'd have to have a set of Mori cams to be able to copy the profile, as the only info I've seen on them is lobe height and duration, which isn't enough; you want to know the full profile specs, and I wouldn't have thought that's available unless you have a set to copy.

[VTRDark]

I wonder if Mik in Canada could make a technical drawing of his recent purchase. You would need the length from top to bottom from the highest points and the width from side to side plus the angles. Just a thought. It would be interesting to see the standard and moris overlayed to make a comparison of the two.

Don't the mori's have a lot more lift than standard so that would mean adding material. Lloyd what you got to remember is that you can easily have material taken off but can't get it added not without massive costs I expect. And as Tony says by taking material away, it's at the expense of cutting into any hardened/tempered surfaces.

(:-})

[tony.mon]

The opening post in this thread has a list of all of the cam data I have been able to get my hands on. There's a lot more to it that just lift and duration, the ramp isn't a single angle, it's a continuously variable curve, and the cam shape, attack and rear faces all have a part to play in accelerating the valve controllably, but not letting it snap shut too quickly. Also remember that the valve has to stop its upwards motion and reverse under spring tension.

[VTRDark]

the ramp isn't a single angle, it's a continuously variable curve

I never realised that. I can understand how it needs to slow at either end so the valves don't just slam open and closed. It's like bouncing a ball on the floor, it falls and as it bounce back up it falls off/slows down before reaching the end and coming back down. Blimy that seriously complicates stuff. It just goes to show the precision that goes into designing these things.

(:-})

[tony.mon]

Latest additions:

1mm oversized flat-faced inlet valves installed. The original seats are wide enough to be recut this far without the need for new seats.
The surface has just been lightly skimmed, there's no real reduction and therefore compression will be the same. A tiny increase due to the flat faced valves, perhaps.

I'd best get on and fit them, as soon as I get the new stem seals. I have some in stock but not enough.
I have head gaskets, as always I'm short of just some minor parts before I can proceed.
I'll do a dry build and check clearances, but there should still be 1mm+ as the valve face height is the same as the previous ones were. This also means normal shim ranges will do.

[sirch345]

You certainly couldn't have gone any bigger on the valves, they're looking good Tony

I bet you're looking forward to getting the heads re-fitted and the bike out on the road now

Chris.