possible power gains from milling the head?

[Danaconda7]

whoa! take it easy man. Hope things turn out alright.

You right I am not sure what I was thinking. In my defense I am sitting or lying in a hospital bed waiting for test to find out what's wrong with me now. Heart rate keeps going into the 30's must not be getting enough blood to my brain
.

[Nessism]

1) The power increase from milling the head will be minimal. Typically such work is done in conjunction with a high performance engine build where you have a number of changes what work together.

2) The cam timing will be off thus necessitating sloted cam sprockets and degreeing the cams (a good bit if work)

3) Cutting the head is not cheap - figure on about $50. Of course you will also need new top end gaskets, OEM only if you care about an oil tight seal, so that adds about $100 to the cost.

4) The increase in compression may lead to detonation, necessitating the use of more expensive premium fuel and/or retarding the ignition timing.

Overall I'd file this milling the head thought in the same file as the turbo 450. Time to put down the bottle and get back to reality.

[Danaconda7]

ouch... your points are well noted. just so i feel a little better, the milling work would be free. between my father and a good friend of mine I am sure it could be handled. The cam timing bit would be a hassle for sure. New seals, of course. And i understand that higher compression requires a higher octane rating. Thank you for your input, oh by the way... what other work would go together well with this bad idea?

[Guest]

ouch... your points are well noted. just so i feel a little better, the milling work would be free. between my father and a good friend of mine I am sure it could be handled. The cam timing bit would be a hassle for sure. New seals, of course. And i understand that higher compression requires a higher octane rating. Thank you for your input, oh by the way... what other work would go together well with this bad idea?

The bad idea is just milling the head and expecting any big gains but if you mill the head and add some pistons since the head is off then add some aftermarket cams and bingo you got a noticeable difference.
If it were me I would find a Bandit 1200 motor and put it in your chassis would probably be cheaper and make more power and I think the Bandit motor weigh less. It only weighs 175lbs

[wymple]

"You right I am not sure what I was thinking. In my defense I am sitting or lying in a hospital bed waiting for test to find out what's wrong with me now. Heart rate keeps going into the 30's must not be getting enough blood to my brain"

The late Robin Williams noted that the brain and the pen*s both run on blood, and there is only enough for one at a time. Maybe you should adjust your thinking?

[Danaconda7]

Interesting, I will look into the motor swap you sugested. As for pistons and cams, I am yet to find anything that I can be sure would fit my bike. the 85 gs700es seems like a one year bike and there is little to no aftermarket preformance parts available.

The bad idea is just milling the head and expecting any big gains but if you mill the head and add some pistons since the head is off then add some aftermarket cams and bingo you got a noticeable difference.
If it were me I would find a Bandit 1200 motor and put it in your chassis would probably be cheaper and make more power and I think the Bandit motor weigh less. It only weighs 175lbs

[Guest]

The late Robin Williams noted that the brain and the pen*s both run on blood, and there is only enough for one at a time. Maybe you should adjust your thinking?

Your right I will shut up now no one needs my advise. I am having a hard enough time dealing with my health issues without people making jokes. I hope it was a joke. My memory is one of the problems I having problems with from having some TIA's or mini strokes so thank you for your comment. It ruined my day.

[wymple]

You bet your bippy it was a joke, just trying to make ya feel better.

[blowerbike]

Interesting, I will look into the motor swap you sugested. As for pistons and cams, I am yet to find anything that I can be sure would fit my bike. the 85 gs700es seems like a one year bike and there is little to no aftermarket preformance parts available.

84-86 700E/ES are the same.
also add the 83 750E/ES as a possible donor.
not a one year bike.

[81GS850]

If he was to match it up with a set of cams then he would be a happy camper. I think you get more from milling a motorcycle head because the chamber is so much smaller. But I am no car guy I only build bikes

Your still talking about compression ratios being the same. Taking a car and a motorcycle from 9:1 to 10.5:1 net the same results. You probably feel it more on a bike though.

[81GS850]

Huh??? Since the cams are connected by a chain, why would one be retarded and the other one advanced?

I would think that with a milled head (or block), the cam gets a little closer to the crank, but the chain does not shrink, so the cam rotates backward to take up the slack. In my mind, that "retards" the cams. Both of them. Am I mistaken in my thinking?

.

I'm not sure I can wrap my head around either theory so can someone explain? With an ohc motor the chain slack would be taken up by the chain tensioner if possible. And removing the head you would degree them anyways, at least line them up dot to dot so to speak. So why would you need to slot the sprockets? I could see you shortening the timing chain, but I don't see the cams "running backwards" to take up the slack. Also the only reason I see for a slotted cam gear is to get your cam timing dead on balls accurate. But who knows of each lobe of the cam is machined at the same degrees on each cylinder. Can you explain please? Thanks.

[blowerbike]

Huh??? Since the cams are connected by a chain, why would one be retarded and the other one advanced?

I would think that with a milled head (or block), the cam gets a little closer to the crank, but the chain does not shrink, so the cam rotates backward to take up the slack. In my mind, that "retards" the cams. Both of them. Am I mistaken in my thinking?

.

when degreeing the cams on a DOHC engine you must move int. one way and the exh. the other way to achieve advance or retard.
example.
int. adv.=adv.
exh. adv.=retard.

understand that each cam ramps different so you have to change directions when going from int. to exh. or visa versa.

[GregT]

when degreeing the cams on a DOHC engine you must move int. one way and the exh. the other way to achieve advance or retard.
example.
int. adv.=adv.
exh. adv.=retard.

understand that each cam ramps different so you have to change directions when going from int. to exh. or visa versa.

Would you care to have a rethink on this statement ?

In my experience, if you wish to open the exhaust earlier - ie as you state it, exh.adv, - you must advance the cam in relation to the crank.
Doesn't matter if the cams rotate in different directions (not the case here anyway) advance or retard is in relation to the crank's direction of rotation.
The only time you would move the cams in different directions in relation to the crank is if you wished to advance one and retard the other. Not an uncommon scenario seting up a twin cam.

[blowerbike]

greg my post is taken from a quick visual i wrote down when i degree cams.
so here it is again but changed to make sense for anyone but myself.

int. adv.=adv.
exh. adv.=retard.

i understand the above.
here let's try this.

int. cam clockwise crank rotation= advance(larger lobe center)
exh. cam clockwise crank rotation= retard(smaller lobe center)

i hope this explains it.

[GregT]

greg my post is taken from a quick visual i wrote down when i degree cams.
so here it is again but changed to make sense for anyone but myself.

int. adv.=adv.
exh. adv.=retard.

i understand the above.
here let's try this.

int. cam clockwise crank rotation= advance(larger lobe center)
exh. cam clockwise crank rotation= retard(smaller lobe center)

i hope this explains it.

Yep - it explains it in terms of changing the lobe center numbers which i don't think the OP was asking....