Big bore

[TopCatGr58]

Pat,

When I did mine now almost 6 years ago, I didn't know any better, and put 20-50 Castrol in it. Seemed like it took a long time to break in, but just like PGGG, I too had compression readings of 180 range after breakin, and I only put the 1179 kit in! I'm running the stock cams/heads from an 81SH.

Taking 180psi divided by sea level 14.7 gives you 12.25.... however I know that is NOT how compression ratios are calculated. However, 142psi which is listed as the stock value, divided by 14.7 gives you ~9.6.......hmmm?

The head gasket is a special Graphite compound, and I think it does undergo some compression during torquing. I also don't remember having to install or use either the bottom O-rings, or a bottom gasket, just a thin layer of (don't shoot me) Permatex.....
again, I plead ignorance of 6 years ago!! Have not had any leaks from around the base of the cylinders at all! The cylinder jugs stick down into the upper case a good inch or more, and there isn't much pressure there. You've already invested in both gasket and O-rings, so go ahead and use them, but I'm pretty sure you could have just used some Yamabond type sealant!
T.C.

[MAXIMAN]

If you guys had longer duration cams (pggg and TC) your pumping compression would not be that high due to exhaust/intake overlap.

As you well know static calculated compression is "non-negotiable" and is a function of a variety of fixed but measurable factors (chamber volume, piston volume, deck, gasket thickness, vol. eff, etc).

Pumping compression is a whole "nuther" animal. My ZRX has a calculated static 10.5:1 CR. But the pumping compression is only 140 to 145 psi. It really has little effect on the bikes performance though. Bone stock it makes 127 hp and 85 ft-lbs of capital "T" at the rear wheel.

Many variables affect pumping compression because it is not static. It is dynamic. Valve timing is a big thing is them most.

[pggg]

Still haven't bothered sitting down and working out the compression ratio thing, probably heard 10 different explanations from 10 different mechanics and still don't know. My cams are stock 80's, perfect for down here as it's very twisty and hilly on a lot of roads. My motor is still 'de-tuned' for tractability but has mega-grunt. I was itching to give the motor 'the works' as the ported head can match up with hard-out cams and re-worked valvetrain including under-bucket shims to get maximum kick at redline revs - topped off with gaping bell-mouthed flatslides. Also lightened crankshaft and other tricky things... but this XS is my only roadbike so it's a cruiser first and foremost. XS11's are such a smooth effortless roadbike I don't wanna change it. Still impressed with the bike after EVERY ride.

[Dennyz]

static compression ratio is pretty straight forward. The area of the bore times the stroke, divided by the combustion chamber volume.

The piece that is missing is the combustion chamber volume.

According to my math, one cylinders displacement of a stock XS is 275.431cc. If the CR is really 9.2:1, that would make the combustion chamber volume something like 29.938cc (30cc).

Not knowing the 1196 kit's bore, I can divide the total by 4 and get a cylinder displacement of 299cc. That displacement stuffed into a 30cc chamber should yield a static CR of 9.9:1.

I am wanting to put the 1196 pistons in my 'F' this winter. I want a static CR of at least 10.5:1, so I will be milling the '80 head I plan to use (with '78 cams).

Of course, I will measure the volume of the combustion chamber to be sure.

[MAXIMAN]

The following is my opinion only and doesn't reflect anything but that...

The bore of the 1196 is 74.5mm. But you could figure this out back backing into the equation since we all know the stroke is 68.6 mm.

I dunno how you did your math but a 30 cc chamber would yield 11.25:1 at zero deck on a 71.5 mm stock bore. On a 74.5 mmm bore it would be even higher(would you believe 12:1?).

At .006 in the hole (reasonable est) the CR would still calculate 11:1. This not the case as everyone knows Yamaha published 9 to 9.2 CR for the Eleven.

The piston volume for a stock eleven is 8 to 8.5 cc. The chamber is about 37 cc. Stock head gasket is .050. Using these values you should compute somewhere around 9:1 CR which is exactly what Yamaha engineering claimed on the 80-82 models.

The 78-79 XS chamber was about 1 cc less and thus computes 9.2:1 static CR.

If you are serious about getting the static to 10.5:1 you will have to shave the head the maximal amount.... .030. If you mill it that much then pray you don't over rev or you may have more problems than queen for a day.

In my opinion the only way to reasonably achieve 10.5 CR on an Eleven is to have Venolia build custom pistons with a "real" crown.

The problem with acheiving 10.5 using Wiseco is the crown of the Wiseco piston is identical to the OEM profile. We cc'd my 1196 pistons and they turned out 8.2cc.

Lastly...but not "leastly"...I don't know about you but I would be very leary of running an air cooled street bike at that high of CR. While it is true you can certainly take an air cooled motor even higher...it is also true you will adversely affect the longevity of the engine. If I was building a drag bike then who cares. You'll be rebuilding the engine every few races anyway.

But then if I were building a serious...air cooled drag bike ... I wouldn't even consider an Eleven.

Good luck with your Wiseco install. If you're like me you'll be please with the result.

[skids]

Stock:

CR = V2/V1
and V2 = V1 + Displaced vol
Displaced vol = 1102/4 = 275.5

So, back to the comp ratio equation,

9.2 = (V1 + 275.5)/V1

Solve for V1, the chamber volume, V1 = 33.6 cc

Now look at 1196 displacement:
if V1 is unchanged,

CR = (33.6 +[1196/4])/33.6 = 9.899
CR = 9.9 or 9.9:1

I don't know what it all means, but I use regular gas! :-)

[mro]

originally posted by skids
I don't know what it all means, but I use regular gas! :-)

My 80G is bone stock and does not like regular.
Just had the thought that I've never checked to see if the stationary pointer "T" mark lines up properly at TDC. If off could be why timing light says it's set OK, but could be off a little.......

Either or other..... probably could adjust timing to stop ping??



mro

[skids]

I don't want to throw anyone off with that statement. I use regular gas because I have stock compression in stock engines.

Originally posted by skids


I don't know what it all means, but I use regular gas! :-)

[Pat Kelly]

I (usually) use regular in both my E and LG. Really hot days when riding hard I get a little knocking. Normally regular gas works just fine for me.

[Dennyz]

Oops! I did forget to add the combustion area to the displacement volume.

So, to get 10.5:1, I would need to reduce the combustion area (33.6cc) by 5.7%, to 31.7cc.(1.9cc) It is a bit more complicated to calculate exactly how much I would have to mill off the head. I haven't gone there yet.

Decking may also be an option. It looks like I would only have to remove around .45mm (~0.018") from the deck. Hummm?

I am not too concerned about the heat from a 10.5:1 CR on the XS motor. In true XS fashion, I feel the cooling area is over built and can handle the increased head temp. Proper jetting and a good exhaust system can help reduce head heat. An oil cooler will also help out. As for engine life, the bike already has 130K miles and if I get another 70k I would be tickled pink!

I am more concerned about valve to piston clearance than heat, as I am interested in playing with cam timing. I will have to spend some time actually cc'ing everything before I start cutting.

(OK, check my math!)

[MAXIMAN]

Denny - 130K!!! Wow these old bikes truly are remarkable.

I think Dan Hodges told me once that the stock Eleven deck ranges from .023 to .006 in the hole. So if you take 18 thou off the top of the block you'll be running "proud" pistons.

Before you do that I would recommend talking to Dan. He's a walking encyclopedia concerning XS rebuilds. He has forgotten more than most of us know and is an invaluable asset to the community.

The heat shouldn't be a huge isse but I would certainly run a good oil cooler to hedge my bet. Besides there is nothing to loose by running a cooler. The draw back is header fitment.

The new header I just for Zilla actually clears the oil cooler adapter plate by a mile! (well a...like they say...a quarter inch is good as a mile ).

I'll be posting pics of the system later to day. The Kerker I snagged would NOT clear the cooler any way at all.

[The Lorax]

Originally posted by MAXIMAN
I know one guy that builds car engines that runs them for a few minutes with...are you sitting down?... NO OIL!

He says it helps the rings seat. He's never had one lock up or had it returned.

When I rebuilt my engine, the fellow that was advising me, (first engine teardown) told me to install the pistons and rings dry, put it together and before I start it the first time, disconnect the coils and turn the starter until the oil light goes off. same explaination, it helps the rings seat. this fellow also has been building drag bikes for many years. I followed his instructions, 1000 miles later, I'm still smiling!!!

[79XS11F]

Originally posted by Pat Kelly
I ordered the 1196 kit today. Yosemite Machine will be boreing my XStra cylinders when the kit arrives.
Then to wait for a rainy day to start working on the bike.

On to another question: breaking-in the rings (oil thread ). Should I use a straight weight oil for scrubbing-in' the rings or my usual 10-40? I know with cars a straight weight is recommended.

I have the 1179 Wisco kit and they recommend single weight oil for the break in and I will follow their break in recommendations. A lad at the local bike shop has a Wisco kit in his older KZ1000 and he told me that the most important thing with these kits is the break in and the re-torquing of the head. He told me to fire the rebuilt engine up and idle it to full temp then shut it down until COMPLETELY cold and re-torque the head. He said the head should be re-torqued every 500 KM after COMPLETELY cold until no more seating of the head gasket can be obtained. Then STICK to the manufactures head torquing schedule. Also very important to have VERY clean threads on the block through studs and cap nuts. Lube them with liquid Teflon during the rebuild.
For what it's worth he races his bike at the local drag track and "seems" to really know his stuff.
Rob

[MAXIMAN]

Originally posted by 79XS11F


I have the 1179 Wisco kit and they recommend single weight oil for the break in and I will follow their break in recommendations. Rob

Who recommends single weight oil?

[79XS11F]

Originally posted by MAXIMAN


Who recommends single weight oil?

Yamaha service manual say to break in new rings with single weight oil and Wisco kit says to follow service manual instruction for break in .
Rob