80-81 1196 Big Bore piston kit

[keatingww]

Hey guys,

New user here as well as "new" 1980 XS1100 Midnight Special owner. I just took my Cylinders into a shop and the guys said I had 2 that were egg shaped and that he could bore them out to 72mm. From what I found, stock bore is 71.5mm. Problem is I can only find the 74mm or 74.5mm pistons. My question is... are there any overheating issues related to these bigger bores that you have noticed. I will most likely go with the cast pistons from Japan as well.

Also, if 71.5mm is stock and the mechanic said he only needs to go to 72mm to resolve the issue, How bad is it really? Should I go ahead and bore them or should the piston rings take care of this issue by themselves.

[DGXSER]

I do not know the measurements, but check into the over-sized rings. They make them 1 -2-3-and even 4 IIRC sizes over stock. Should / May work wiht your bore.


On the flip side, I have not done it, but there are several long time members here who have installed the big bore set up. None have ever complained of overheating or anything like it.

[CaptonZap]

Also, if 71.5mm is stock and the mechanic said he only needs to go to 72mm to resolve the issue, How bad is it really? Should I go ahead and bore them or should the piston rings take care of this issue by themselves.

The "egg shaped", (does that mean oval?) of less than .5mm (apx .020in), means that the mechanic figures that .010in off each side will clean them up. A more pertinent question is, how much ovality is there?
An oval cylinder is not a deal breaker, if it is only a thousandth or so. What will break rings is a tapered bore.
Ring side clearance is another critical factor.
The following site will give you a basis on which to make up a list of questions to ask the mechanic. If he stumbles, hesitates, or tells you he doesn't need to know "that" to be able to tell you that you need to pay him a lot of money, you might want to get a second opinion.
The manual will give you the factory suggested dimensions for most of this, although it might require you to actually read the engine rebuild portion of the manual, since the table of limits, as it is called, is not listed in some manuals, but rather spelled out in the list of step by step instructions..
If you have questions as to numbers, ask here, and someone will get them for you. Good luck,


http://smallengineinformation.com/?page_id=500

[WMarshy]

Hey guys,

New user here as well as "new" 1980 XS1100 Midnight Special owner. I just took my Cylinders into a shop and the guys said I had 2 that were egg shaped and that he could bore them out to 72mm. From what I found, stock bore is 71.5mm. Problem is I can only find the 74mm or 74.5mm pistons. My question is... are there any overheating issues related to these bigger bores that you have noticed. I will most likely go with the cast pistons from Japan as well.

Also, if 71.5mm is stock and the mechanic said he only needs to go to 72mm to resolve the issue, How bad is it really? Should I go ahead and bore them or should the piston rings take care of this issue by themselves.

You can buy a cheap big bore piston kit on ebay, the bore will be 74.5mm. The kit is cheap because the pistons are cast, unlike the expensive Wiseco pistons that are forged. Any good engine builder would not bore the cylinder without having the new pistons in hand. Somewhere there should be tolerances for cylinder wear, you should have him verify your cylinders are outside that spec before you spend $600 or more on your bike...

http://www.ebay.com/itm/80-81-Yamaha...7486d7&vxp=mtr

[80mdnt11]

Ok, Have read through all info here..........very helpful. Have had the head in for some valve, seat & guides inspection & new seals. Turns out all good, trust the mech. whom I worked with back in the '80s.
Had bore checked...........002-.0025 taper & out of round. Yes, had little more piston slap than I liked.
Have been looking hi & low for some 0.50 pistons with no luck. Did come across the 1196 kit. Just concerned of quality and thin skirts. Mech says he can punch 0.050 x 4 = 200.00 1196/74.5mm = 300.00.
Guess my question is has any one had any issues with these 150.00 kits?
Will do a re-read of all searches..........
Opinions welcome!!

[WMarshy]

I dont think anyone has any run time on this kit yet. I haven't heard anyone that has... of course Im away from the site for a short duration during the winter.

[WSL91]

Great thread. I'm guessing that unless you are racing (which I doubt) these pistons will be fine. The next repair you bike will need will most likely be something else anyway. I'd plastigauge the bottom end for sure while it's apart. I'd have to look at the mm specs but in old tractor motors .003 is the max clearance so I'd think you want around .002 in the bottom end max. Plastigauge is cheap. I bought a complete set of external Mics from HF a couple years back along with some used Starretts off ebay with Standards, the HF mics were right on. At least there is something out there for a reasonable cost that keeps these bikes from the recycling yard a little longer.

[trbig]

The kit is cheap because the pistons are cast, unlike the expensive Wiseco pistons that are forged.

Just remember that your original pistons are cast as well, and they seem to hold up just fine. If I had to rebuild another motor, I'd definitely try these out. Looks like you can get your cylinders bored and the piston kit bought for less than just the Wiseco pistons.

[WMarshy]

Just remember that your original pistons are cast as well, and they seem to hold up just fine. If I had to rebuild another motor, I'd definitely try these out. Looks like you can get your cylinders bored and the piston kit bought for less than just the Wiseco pistons.

Thats why I bought a kit, figured its too good of a deal to pass up.

[Courtney]

Further to these big bore kits, I did a little looking while my head is off and I was cleaning up the gasket surfaces. Here are a couple of shots of the steel liners we have in these aluminum heads.



They measure out at 8mm thickness which is pretty good, much like my old bigbore VW performance stuff. Now if you bore these out to 74.5mm for an 1196cc engine you are in effect removing 1.5mm from the walls, so you STILL have 6.5mm of wall thickness. I think that is pretty good myself.
As to cast pistons vs. forged, well there are significant gains to using forged, but I've run both in HP VW engines, and to be honest, with a redline of 7500rpm the cast were always good enough. I even ran cast pistons once in a Ford 390 Y block engine with a 428 SCJ cam and huge Holley toilet bowl (can't remember the size now) double pumper, and abused the **** out of it. Never gave me any trouble.

[Rasputin]

Question. Did you just measure the top lip or did you measure the cylinder wall down lower? I just measured it at the lower end of the cylinder and got 3.5 MM.
I had a set that were bored to 1204 cc's and they were heat checked beyond help and were very thin. I do not have them now so I can not measure them. Just asking.

[Courtney]

Question. Did you just measure the top lip or did you measure the cylinder wall down lower? I just measured it at the lower end of the cylinder and got 3.5 MM.
I had a set that were bored to 1204 cc's and they were heat checked beyond help and were very thin. I do not have them now so I can not measure them. Just asking.

Just across the top Ras, are these lipped then, and what you see on top is NOT what the thickness is?

[MPittma100]

Compression Ratio Calculation

Hey Steve,

The Wiseco web site does NOT have photos YET of their products for the xs11. It's been 12 + years since I put my 1179 kit in, but I don't recall them being FLAT TOPPED, they did have the indents for the valves. IIRC from both previous discussions....they rate their obtained comp ratio per their use in the earlier model engines where the comb. chamber is shallower, and so the 10.25:1 ratio is obtainable. But with the later 80-81-82 engines, the comb. chamber is deeper due to the larger valves and reduced OEM comp. ratio for the emissions changes..9.0:1 vs. the 9.2:1.

Stock comp. is listed as 142 +/- 10 at sea level, and I'm at sea level, and after my breakin, I obtained values of 180+ psi, I don't know how to convert that value with our known bore/stroke to determine the comp. ratio that I got with the 1179 kit in my 81SH. I use Premium fuel, but because I didn't want to take any chances of burning holes in my pistons by "trying" to use regular and listen for KNOCK...but I might be able to run regular...just never tried it! YMMV, but I don't think he would need to worry about having to use racing fuel!

I haven't looked at the ebay ad yet, but I can't see them limiting themselves to marketing to just the 80+ year models vs. the 78-79, if they have the valve indents large enough for the 80-81 models, then there should be plenty of room for the smaller 78-79 valves.

T.C.

There are many "free" compression ratio calculators on line. But to get an accurate number, you do need a good bit of information - Bore, Stroke, Combustion Chamber size, Piston Dome CC, Head Gasket thickness and gasket bore, etc. If you can get these numbers, the calculations are dead on. Some times the piston manufacturer has to be contacted.

[Mathh]

Just across the top Ras, are these lipped then, and what you see on top is NOT what the thickness is?

Hi! Check this topic :

http://www.xs11.com/forum/showthread.php?t=35223

[Courtney]

Hi! Check this topic :

http://www.xs11.com/forum/showthread.php?t=35223

Bloody hell Mathh, I am just going to shut my mouth from now on; a lip. Would have NEVER dreamt it.