Question about the stock cylinder sleeves

[Mathh]

I'm going to cut up a cylinder block to see how much room there is for bigger cylinder sleeves.
But I'm puzzled by this undercut in the stock sleeve:



It reduces max bore with 1mm+ ... and nobody I ask has an answer why it is there...

Anybody?

[crazy steve]

I can think of two reasons why that groove could be there....

One, to insure that you have a sharp 'corner' where the top flange meets the outer bore, in other words not have a 'rounded' bottom on the 90 degree angle. Due to tool wear, it's tough to get a clean/sharp corner on multiple pieces like you'd find in mass-production without frequent tooling changes; a cost-saving measure.

Two, it could be a 'relief' area to give whatever microscopic particles may collect at the top of the bore while pressing the sleeves into the cylinder casting someplace to go, allowing the sleeve to fully press into the casting. Maybe a combination of both reasons...

In any case, I'd bet that is a machining 'artifact' produced during the manufacturing process rather than something needed for operation. I'll also mention that several members have reported that heating the cylinder assembly to 400-450 degrees F expands the aluminum enough that the sleeves come right out, so you wouldn't have to cut one open...

[81xsproject]

There is a lot of sleeve info in Dan Hodges post about re-sleeving to create the "XS1300"

[Mathh]

Thanks for the replies guys, i think Crazy Steve is spot-on.
I did cut up the cylinder block because I wanted to know how much room there is between the #1-2 and #3-4 bores. There is an air passage for cooling between them. Same between 2/3 and the cam chain tunnel. Very little meat left there. I'll post some pics soon.
Thanks for drawing my attention to Dan Hodges' posts, I hadn't read them before. Valuable info, only I'm not sure id he did take these cooling tunnels into consideration, so I'm going to contact him.

[crazy steve]

One thing Dan never mentioned and something that may be an issue for a 'endurance' application is cooling capability. The XS motor isn't overly-generous in it's cooling fin area, and a larger motor will generate more heat. You can generally get away with a displacement increase on a street or drag-race motor as you have only short-time full throttle operation, but running it full-tilt for more than 4-5 minutes may cause overheating. You can probably offset that to a degree with an oil cooler (a BIG oil cooler) but you still might end up with 'hot spots'.

Something to think about....

[TomB]

As Steve says, the undercut is standard engineering practice, even more so on mass produced components, in substitue for square corners. Tungsten carbide tips are used in the tooling which don't have sharp corners but radii (radius's )

Would it be a huge issue if you machined the ali block and broke though into the air gap with the sleeve? As long as it still had fins touching the sleeve it would still carry the heat away, and if the sleeve was outside in the air flow it would also help or would we be thinking too much localised heat with having no heat soak from the ali?? There shouldn't be an issue with strength/sleeve support, after all, wet sleeves in water cooled engines are Ok.

Just thinking outside the box here

[Mathh]

One thing Dan never mentioned and something that may be an issue for a 'endurance' application is cooling capability. The XS motor isn't overly-generous in it's cooling fin area, and a larger motor will generate more heat. You can generally get away with a displacement increase on a street or drag-race motor as you have only short-time full throttle operation, but running it full-tilt for more than 4-5 minutes may cause overheating. You can probably offset that to a degree with an oil cooler (a BIG oil cooler) but you still might end up with 'hot spots'.

Something to think about....

That is the main problem I think I will encounter, not things like strength or anything else. And I think no one here can answer that question. But to make things complete, here are the pics I promised:

Here's some pics of the amount of meat between the cylinders and the air passages..











So Dan Hodges calculated a max of 1311 cc. That's more than what i calculated: 1295cc with a 77.5mm bore. That's because I measured the smallest wall thickness as 2.5mm between cylinders 1 and 2 (3 and 4 had 3mm but i guess i cut it at the wrong place) and 2mm at the stud holes. Don't know yet what Dan measured, have to ask. Only thing I want to know now if a bore like this will make the engine overheat

[crazy steve]

...Only thing I want to know now if a bore like this will make the engine overheat

I think that's very real possibilty from some of my personal experiences and what I've seen on other air-cooled motors. A four-stroke gasoline motor is nothing more than a heat pump, and to make more power you have to produce more heat.

There's a lot of variables, but one thing to be aware of is sleeve thickness. Too thin, and at higher heat you'll suffer bore distortion. Some of the big-bore Harleys use full iron cylinders as they've found that they retain their shape much better, even with the poorer heat disipation of iron. You would probably have to monitor head temp also, as I've been told that roughly 70% of the heat shed via the fins is done at the head. But oil coolers and less timing can help with that, but the retarded timing will hurt power output at high rpm. I'm doing a 1450cc Sportster motor with iron cylinders for one of my project bikes and I've been told that timing management is critical to prevent overheating.

Most of the really large big-bore kits I've seen feature all-new cylinders with enlarged fins to help with this issue, something that's not available for the XS11.

I can give a personal example; I built a big-cube Ford FE motor years ago (452 cubic inches) and installed it in place of a 390. I used the largest available radiator at the time (a heavy-duty unit for a AC car), and the motor would run at 'normal' temps in 'normal' driving. But start seriously hammering the throttle, and the temp would quickly go up, overheating if you kept at it. This was roughly the same percentage increase in displacement as you're looking at (about 18%), so you'll probably overwhelm the stock cooling capability if the motor is ran at wide-open-throttle for extended periods. On a street motor, I think it would work fine, as the amount of power needed during 'normal' operation and/or when cruising will be the same either way, so you're producing the same amount of heat. But for endurance racing, it may be too much....

[Eveready1100]

Math, just an idea that may be a bit over the top, but given your past experience in creating XSive miracles, do you think that shaving the middle cylinder fins a bit and encasing the barrels in a jacket and liquid cooling them using a radiator be too radical for you? That'd solve the hot spot problems as the coolant would soak away the heat much more efficiently than air.

Many years ago, I made a water cooled barrel with really radical porting for a TM125 motocrosser just using some ally plate, PK screws and a lot of silastic. Fitted a radiator off a CX500 and it never leaked a bit. Ran nice and cool too!

[Mathh]

Math, just an idea that may be a bit over the top, but given your past experience in creating XSive miracles, do you think that shaving the middle cylinder fins a bit and encasing the barrels in a jacket and liquid cooling them using a radiator be too radical for you? That'd solve the hot spot problems as the coolant would soak away the heat much more efficiently than air.
Many years ago, I made a water cooled barrel with really radical porting for a TM125 motocrosser just using some ally plate, PK screws and a lot of silastic. Fitted a radiator off a CX500 and it never leaked a bit. Ran nice and cool too!

Hi ER1100, as Steve is again telling what I was thinking, watercooling crossed my mind ... for one nano second but I like the looks of the aircooled engine too much to go and spoil it with a radiator and pump and hoses ...
although the rad on the turbo bike looks butch