shaving head effect on cam chain/timing.

[minidirt]

Just wondering if anyone has any experiance with what shaving the head on a minibike will do to the cam timing and tightness.
I know the chain will be looser, will the standard tensioner take up the slack if i take 20odd thou off the head (1/2 a mm) and how much would you expect this to retard the (cam) timing a degree or two...

 

[noidea]

Hey, i was going to do the same thing. Make sure you clearance your piston aswell when you shave the head. Put a bit of blue tack or plastasine on the impression areas and turn your engine over slowly with the head not bolted on. You want to make sure the valves arent going to hit the piston.

heres some info from the porting thread going on atm

"That head shave doesn't affect timing much. Once you put in a new cam it will then need to be degreed in and timing mods made if needed. The reground cam can be made to suit if you know what your doing."

"So I don't want to drop the head any more than I have to other wise I'll have to relieve the piston and valve reliefs as well. Of course if you modify the heights substantially you will have to rectify the cam timing as well.

So I reckon the best course of action is to leave the deck height and head height alone 'cept for a tidy up. Install $70 or $80 hc piston (might as well be56mm while your at it, gonna cost the same!) so the cam timing is good. Drop in a Z40 cam and valve springs from a trx90 (wider coil spacing and stronger) and you'll be making that nice port job all worthwhile. Next step if you get bored of that setup is to install an inner rotor ignition kit and start lightening everthing."

 

[Max99]

No idea...it'd be interesting to see some dyno results once a few hp builds are completed around the place.

 

[minidirt]

this is just my ducar dhz, i dont really want to spend any money on this one,just see what i can do if i rip into the free side of things, got a milling machine at school, air porter laying about someplace, it keeps up with lifans and that, with lots of clutch and carefull gear changes, i wanna see how i can make it go staying with stockish parts.

 

[noidea]

"see how i can make it go staying with stockish parts"

Me too, not real keen on gettin a h/c piston but it seems like it would be a bit easier than milling/releiving a piston.

max99 if your in syd and got acess to a dyno no worries.

 

[Max99]

max99 if your in syd and got acess to a dyno no worries.

Not in Syd....there used to be a tuner up the road from me with one, and I'd like to find out if he's still there. I haven't started my hp build yet but I'm just gonna have to know what it's puttin' out when I'm done.

 

[noidea]

awsome.

Get a reading before and after. Duno how reliable those claims by the manufacturers are...

Be good to see the power curve changes aswell.

 

[Mack]

You can shave the head without a prob. if your going to stay with the stock piston. If your going to do it go for all you can. Shave the cylinder also and bring the piston up to the top of the bore.

The cam chain tensioner is hydrolically operated under pressure from the oil pump and will take up the slack. You can slot the holes on the cam gear to degree the cam back in. Some guys worry about this incase the camgear moves, but heaps of guys run without trouble this way. I would give it a go if I wasn't interested in spending too much.

 

[noidea]

Probably end up easier to make your own high comp piston. What are these pistons made out of? Any way of weld building them up and them shaping them? Dont think i wud trust JB weld in the combustion chamber lol

 

[Mack]

You could turn down the edges of the stock piston and deepen the valve reliefs depending on how much the stock piston has to play with. Then shave the cylinder base to bring the piston right up as far as possible. Shave the head also and you may make reasonable gain.

I,d rather spend 80 or 90 bucks and leave the camgear alone.

 

[minidirt]

could always tig some more meterial into the head to rais the compression, i know this can work, but you have to shape the weld you add corectly, not to sure on that part...

 

[noidea]

Thats what i was talking about. Weld on material, careful not to warp the piston. Then reshape the valve reliefs and possibly remove from inside the piston to return it to same weight, but thats not so crucial on single piston engines.

 

[minidirt]

think i'll try and fill in the head if i do this, rather than add weight to the piston, love revving this thing.

 

[Mack]

The main thing with building up the head is shrouding the valves and masking the plug. A good experiment would be to build up the side opposite the plug hole but make it so that it creates squish and forces the mixture towards the plug side.

If you mask the plug area you will not get a good burn, defeating the purpose.

 

[noidea]

You would be able to reduce the weight of the piston back to stock and possibly less.

 

[minidirt]

if i made it less then i'd have the crank out for a diy ballance, probably ending up in making an engine that vibes like washing machine on spin dry.

 

[Mack]

If you try any of that with one of these pistons, I predict you'll grenade your engine in less than 5 mins.

If your determined to try it, stick with building up the head. IMO