piston to valve clearance

[XS1100 Newbie]

Anybody know what the clearance is on the XS1100? Has anyone tried milling the head down, or putting in a thinner head gasket to gain compression ratio? Just curious. Where might a person find these specs. The manual does not show it.

[Guy_b_g]

Hard to gain much that way because it changes the distance the cam chain has to travel, and the cam timing, you can't gain much before it becomes a critical issue.

Better to go with the big bore kit (cheapest for the bang), but others have gone the big$ route, stroking the crank, aftermarket custom pistons, blueprinting, mild port work,etc., some have also turbocharged.

There is no solution that doesn't entail a good deal of effort and money.

Seems to me the cheapest route to go is with incremental upgrades. Less restrictive/lighter exhaust, aftermarket carbs (late '80's GSXR750 slingshot carbs were a very good solution for Alanb with dyno runs to prove the results), also remember that each 7 1/2 pounds you can drop off of the bike is equal to adding 1 hp. It's not that hard to drop a good bit of weight off of these bikes with a bit of creative thinking. Another gain can be had with the addition of a chain kit, which reduces Hp friction losses through the drivetrain.

Then once you have all the power you can get for the amount of money you want to spend, you need to address the issues of braking and handling...more$.

By the time you have anything remotely approaching the performance of even a good modern 600cc sportbike you will have invested a substantial amount of money, and still get your butt kicked by a rider of equal talent on the modern bike.

Best to enjoy the XS11 for what it is and improve it incrementally over time.

Probably a lot more than you wanted by way of an answer, I suspect.

[XS1100 Newbie]

You are absolutely right Guy. I was just wondering. Had not thought about that cam chain. I don't have to worry about things like that on my cars. LOL Also something to think about i suppose is what i would give up. The reliability, the fuel mileage, etc..

[mro]

Back in the day

Yamaha had a "Race Kit" for a few professional racers.
8 plug head
Two different TCIs
New type generator
Timing mod
New pistons/rods
I think it wound up with 12 1/2 to one compression ratio

I got this info from the Brit site.
Even got some of the installation instructions too.

Right now it’s just a pipe dream but I’ve got the spare parts plus an engine with a 1203 cc piston kit and falcon crank. Heads been done too. Dual plugs sounds like the next mod for it

mro
BTW, don’t know how much can be shaved from the head, but the cam chain issue can be resolved by slotting the cam gears. (I’ve got some of those too )

[TADracer]

But to answer your question

If you are stock on everything then you probably have in the neighborhood of .080" piston/valve clearance which will occur either slightly before or after TDC, depending upon if it is the intake or exhaust valve you are measuring. Thats what my 79SF had when I checked it the first time. I would not do anything that would yield less than .050" clearance because if you float an intake valve at high RPM, well.......

You can use a thinner head gasket or mill .010" off with ease but you probably will not get a big kick in the pants power gain from it alone. You will have to do other things to take advantage of the slight rise in cylinder pressure you gain.

Most stock head gaskets mic out around .051" when compressed so if you want to try this, I would look for someone that will make you a copper gasket that is .040" thick (and yes, done right they do seal very well). I would try this before milling the head because that is not reversable.

And I say it every time, if you change anything from stock, check your piston/valve clearances on 5 degree increments startting 20 degrees BTDC to 20 degrees ATDC. The closest usually does not occur exactly on TDC.

Just my thoughts.

[XS1100 Newbie]

Good information Mike. Thank you.