Head Games

[Dan Hodges]

Re: Gotta get a new Dictionary

Originally posted by Espiritus
Whew. I promise, I will never, ever try to understand a post about this subject again. I printed it, got out the dictionary, got out the book, highlighted every other sentence, all to no avail.

This seems like a terribly time consuming task to get what appears to be a minimum about of additional power. If you do it, can you tell me later if it was worth it?

Cam

What word, term could you not find in Webster? Was it "polyspherical? One point of compression is worth 4% more power, that's the answer.

[Dan Hodges]

Xcess Chain

Originally posted by 81xsproject

It isn't always about least work for most power. While Dan is a million times more knowledgeable than myself, I think that we are a bit alike in that it is the tinkering and experimentation that is the fun payoff.

Tr, unless Dan has something against master linked cam chains or using a chain tool, you are obviously correct that the cases don't need to be split. As far as the cam timing, shaving the head, block, or both decreases the distance between the cam and the crank. While you can take more slack out of the front of the chain with the tensioner, the rear side of the chain is straight. So, the distance on the leading (rear) side is shortened, yielding excess chain, allowing the cams to be retarded.

Thanks for helping me out with your very good explanation of what happens when the cam chain is lengthened. Cutting the head .030 has always been a cheap and easy way of picking up a half point of compression in air cooled motorcycle engines and the rule of thumb when you do this is to advance the cams 4 degrees to compensate for this increase in cam chain length. I don't like master linked chains and or breaking the chain and adding a length and both Byron Hines and Nigel Patrick advise using such mod as a last resort only. When I had my motor apart it got a new chain, slipper (duckbill) tensioners and the works and I'm certainly not going to break the chain unless I have to. I have MegaCycle cams and Wiseco pistons and have about .090 V/P clearence with the cams installed @ 106 degrees IC and 108.5 on the exhaust. This is suffcient but I don't want to reduce it as I'm thinking about getting another cam with more lift. When you cut the block you move the piston higher in the bore and the top ring gets closer to the chamber and therotically seals better but it will pick up more heat and I would think that if the engineers at Wiseco who designed these pistons thought the top ring should have have been placed higher on the skirt they would have put it there. If you want perfection, you will want the piston deck heighth to be .000 to + .005 and you might have to take a couple thousands from the face of the block to get this, I did. In my case I don't have the V/P clearence to spare anyway and so cutting the block for more compression is not in my program. A stock motor has about .130 of V/P clearence and you need a minimum of .060 and this in effect determines how much you can shave everything..............except your moustache. If you get stingy with the V/P clearence and miss a shift or over rev the motor, particulary with the stock springs you will bend some valves and this is even more of a danger with an old used set of stock springs. The worst case scenario is floating the valves and spitting out a valve shim and in that case it's all over but the crying. Honestly, I do believe in the least amount of work for the most amount of power or the most go for the least dough however I have broke more sh-- than I care to recall and so I leave no stone unturned. Can you put a motor together using Yamabond in lieu of a base gasket? Sure but it will leak eventually why else would Yamaha, Kawasaki and the rest all use a base gasket if they were not needed. The payoff for me is a stock appearing Eleven with horsepower comparable to a stock Susuki 1200 Bandit which according to Dale Walkers dyno makes about 95 horsepower in stock form. My Super Special is better looking, has shaft drive, is more comfortable and has as much horsepower and more torque than the much newer 1200 Bandit and I didn't spend as much money as it would have cost to buy the stock Bandit. What will tomorrow bring, more cc's, who knows.

[psycoreefer]

I love these posts...

What I got from that was:
Dan doesn't like master link cam chains, and doesn't have the piston valve clearance to shave his block.

For the rest of us with stock cams - we would be ok to shave the block or head for more compression as long as we adjusted the cam timing back to spec. and keep an eye on our V/P clearance. Also as long as we don't intend to install a higher lift cam in the future.

[trbig]

When I measured my valve to piston clearance, it was with later model pistons that are higher domed, and early model cams ('78) that are supposed to have a higher lift, on a later model head with bigger valves. There was concernes with the bigger valves getting bent with this setup. I measured at .130 with this setup, more than double needed, so at stock, it would be even a higher number.

So shave away to your hearts content.. lol.

Tod

[red bandit]

I was also going to shave my head and do a mild porting job this winter and never thought of it retarding the cams. Does anyone have the specs for the original stock engine degrees for the intake and exhaust. And do you know what is the most one dares to go. Just for some guide lines. Of course I will check mine before dissassembly. It would be nice to know what it is supossed to be.

[psycoreefer]

I'm not expert but a quick browse through the search turned up:

No one (that I could find) knows the stock cam numbers.

You can't go more then 10 degrees from where stock is or you'll bend a valve. We know this because jumping a tooth on the cam chain will bend valves and 1 tooth is about 10 degrees. Although I'm not sure if they bend from piston valve interference or from intake/exhaust valve interference. If you do a search you'll find a good thread on cam timing that talks about which way to go, what the trade offs are and how far you might want to go as a starting point.

[eroellig]

Re: Gotta get a new Dictionary

Originally posted by Espiritus
[...]

This seems like a terribly time consuming task to get what appears to be a minimum about of additional power. If you do it, can you tell me later if it was worth it?

Cam

Come now... this is like climbing a mountain. He's going to do it because he can.

And, incidentally, learn a bit more about what makes 'er tick.

Eric

[Dan Hodges]

Piston To Head Clearance

Originally posted by trbig
When I measured my valve to piston clearance, it was with later model pistons that are higher domed, and early model cams ('78) that are supposed to have a higher lift, on a later model head with bigger valves. There was concernes with the bigger valves getting bent with this setup. I measured at .130 with this setup, more than double needed, so at stock, it would be even a higher number.

So shave away to your hearts content.. lol.

Tod

Another thing you need to keep in mind when cutting the head and particualy the block is piston to head clearance and a steel rod motor needs a minimum of .035-.040 between the piston and the head. Another thing to keep in mind when using a piston with a lot of dome or shoving the stock one up too high in the chamber is it shrouds the plug and slows down the flame propagation during the combustion process and will cause a loss in horsepower. This is the reason that state of the art motors have small compact combustion chambers with narrow included valve angles and pistons with little or no domes which requires only 30 degrees of ignition timing versus 35-45 degrees of timing for motors like the XS. This is also why motors that have XS style heads respond favorably to dual plugs. The valve reliefs in the late pistons are designed to accomodate the larger diameter valves of the late head but the depth of the relief is the same as that of the early piston. You can build an Eleven with 13 to1 compression but the piston dome has to be machined with what some folks refer to as a power slot so as to accomodate the plug and the flame front. I hope you have a good time with that modeling clay while measuring that piston to head clearance, I did. Dan

[Dan Hodges]

To Jump A Tooth

Originally posted by psycoreefer
I'm not expert but a quick browse through the search turned up:

No one (that I could find) knows the stock cam numbers.

You can't go more then 10 degrees from where stock is or you'll bend a valve. We know this because jumping a tooth on the cam chain will bend valves and 1 tooth is about 10 degrees. Although I'm not sure if they bend from piston valve interference or from intake/exhaust valve interference. If you do a search you'll find a good thread on cam timing that talks about which way to go, what the trade offs are and how far you might want to go as a starting point.

When you jump a tooth on the cam sproket you are not increasing or decreasing the duration of the cam/cams, you are changing the phasing. Some time ago I posted the timing, lift and event angles of both early and late cams and you can check it out. You might also want to read MegaCycle and Web Cams catalog. Yes you can use a cam with more than ten degrees than stock with stock pistons.

[psycoreefer]

was also going to shave my head and do a mild porting job this winter and never thought of it retarding the cams

I thought he wanted to know how far he could adjust the timing of the stock cams if he had them slotted so they were adjustable.

[strippedFJ]

Originally posted by egsols
Hey psyco,

Haven't dealt with slotted sprokets before but how do ensure that they never slip and thus loose your timing? Wouldn't it be preferable to get them set up to where you want them and then drill new mounting holes?

Just asking in case I ever get to that point.

I've slotted cam sprockets on big Suzuki's and Kwaka's in the past, never had a problem as long as the sprockets were torqued up properly (which they should be anyway to prevent the mounting bolts being loosened/damaged). Be sure that the slots are the bare minimum length necessary and damage from slippage can be "contained".
Definitely advisable if you're shaving the block/head.

Slots are advantageous over having new mount holes drilled in that you can adjust over a range, rather than just having 2 fixed positions.

[Dan Hodges]

Advanced Or Retarded

Originally posted by psycoreefer


I thought he wanted to know how far he could adjust the timing of the stock cams if he had them slotted so they were adjustable.

Degreeing cams comes under the heading of fine tuning and generally you would not want to advance the intake more than 5 degrees and seldom would you want to retard it unless you had the wrong cam grind to begin with. Advancing the cam will give you a little more low end torque at the expense of top end and since the late cams only have 235 degrees of duration @ .040 lift an XS with these cams is torquey on the bottom already. You can buy slotted sprockets from Web and Megacycle cams to fine tune your combo and if you use the stock sprocket bolts with a touch of blue LockTite torqued to factory specs you will have no problem with them coming loose. If the stock cams will go in within two degrees of the factory setting they are good to go. If you have an Eleven that has been converted to a baby Gold Wing you might like the slight increase in torque advancing the intake cam 5 degrees will give you but if you have a naked bike with the late cams that's not the way to go. Advancing the intake cam 5 degrees will lower the torque curve by about 300 rpm. The Eleven responds to cam timing like any other motor and consequently the way it's equipped and the type of riding you do will determine what the motor likes in the way of camshaft timing. The late cams were ground with very little overlap all in the interest of emissions as the stock Intake Centerline is 105 degrees and the Exhaust Centerline is 113 degrees with each having 235 degrees of duration. With these numbers you can do the math and compute the opening and closing events for both the intake and exhaust which will give you an idea about what's going on camshaft wise. Happy tuning. Dan

[Dennyz]

XS11s with the 750/850 F/D might like the intake cam advanced.

[Crazcnuk]

Advancing the cam(s) 3 deg is a 'normal' change to 70's and early 80's engines to counter detuning for emission control purposes.

Used to put in 3deg offset cam keys in v8's as a matter-of-course.

[Dan Hodges]

Advanced Emissions

Originally posted by Crazcnuk
Advancing the cam(s) 3 deg is a 'normal' change to 70's and early 80's engines to counter detuning for emission control purposes.

Used to put in 3deg offset cam keys in v8's as a matter-of-course.

How much of a horsepower increase did you realize from this modification? In as far as emissions and camshaft tuning goes, it is the amount of overlap that effects the amount of unburned gases during the exhaust event. The late XS cams (80-81-82) had several degrees less overlap than the 78-79 cams and will not make as much horsepower as the 78-79 cams and lastly, when you advance the intake cam you actually increase the overlap because you are closing the intake valve earlier which in effect opens it earlier by a like amount. Overlap is calculated by adding the intake opening event with the exhaust closing event and you can see how altering these events will effect the torque range and the overlap cycle. In a big block Chevy you only have one cam and you can see what happens in that scenario when you advance the cam. Currently, I use a Jesel camshaft belt drive on my 565 c.i. BBC but years ago in the late sixties and early seventies I used a Cloyes chain drive on the cam and advanced and retarded more combinations than I can remember but all of the advance key kits I have ever seen came in increments of 2 degrees, i.e. 2,4,6 and 8 degrees. After that I used a gear drive for the cam that was made by Donovan Racing in California and it had a mulitude of adjustment possibilities as does the present Jesel set up but the bottom line is, advancing the cam 3 degrees on a big block Chevy will not fetch you a horsepower increase either on a dyno or at the race track. Because of the fact that the overlap cycle on the late cams is short and the stock intake centerline is 105 degrees you can advance it up to 5 degrees and pick up a little grunt below 4,000 rpm but anything less than 4 degrees is a waste of time. Above 4,000 rpm you will lose about 3 horsepower which has been witnessed by A to B dyno test posted on this forum. .003-.005 of valve lash is worth 1 degree of cam timing and so you can see what a miniscule amount 2 degrees of cam timing really is...... the motor simply won't know the difference. As a matter of fact cams of the same likeness (stock or aftermarket) will sometimes vary as much as 2-3 degrees and this is one of the reasons they should be checked when you install them. If you are serious about picking up some low end grunt, have MegaCycle grind you a set of high lift short duration torque cams and be done with it.