Big Bore Kit

[James England]

If the process is anything like on wheels, it's not the material that's used which is the issue; it's the method of production. The structure of cast alloy is much more granular with 'open' spaces between the grains (or whatever the correct term is) Hence cast alloy wheels being quite hefty, compared to forged. Forging..effectively whacking a component out of a block, results in a tighter metallic structure which means that the component can be 'finer' without loss of strength. I have forged alloy wheels on my XJR and the spokes are much thinner than cast, the hubs much smaller and the point where the spokes join the rim is very thin indeed. Cast alloy, because of its nature, would without doubt crack.

So, personally, if at all possible and cost-effective, I'd go for forged pistons as opposed to cast. Same goes for conrods.... Forged replacements are available and they are much finer in appearance, possibly easier to balance on the crank etc. I don't imagine there's much of a performance increase to warrant the expense though!

As people have said, for a bike like the XS1100, forged engine components are probably overkill..... Still nice though!

[MPittma100]

Big Bore

Actually, the opposite is true; a cast piston expands less and needs less clearance. And while a forged piston is stronger, there's lots of cast pistons out there doing just fine in typical street motors. It's when you start running things on the very edge that forged parts become really needed.

I stand corrected. I knew better, but my fingers just would not listen.

[crazy steve]

I stand corrected. I knew better, but my fingers just would not listen.

Hey, who hasn't 'lost control' once in a while....

Get a few drinks in me and my mouth has been known to have a mind of it's own...

[crazy steve]

Forging..effectively whacking a component out of a block...

That's 'billet', not the same process as a forging. Billet generally is somewhere between cast and forged in strength but always less than forged, depending on the metal used for the 'blank' to machine the part from.

Forged parts are made by using steel or aluminum castings or billets and 'squeezing' them to their rough final shape under extreme pressure/heat, although 'cold forging' (low or no heat) is used occasionally. This results in denser metal structure, but more importantly forces the 'grain' of the metal into the shape of the part. This is the weakness of billets parts; while you can use the same strength metal in a billet blank, cutting against the 'grain' introduces weak points.

[AggiesaurusRex]

I know nothing, and I need explicit directions. Lol
I just got the Japan 1196 Big Bore kit in the mail, my cylinders are off and I have a shop a friend who did a big bore kit recommend a machine shop. What information do I need to have for the shop when I take everything in? I've tried to read as many old threads as I can and I've seen things like giving clearances, ring gaps, etc etc. Again this is my first project and I definitely don't want any goofs, can someone explain what I need to know?

[Mathh]

I have seen them all on dyno's. Cast and forged. No big hp gains but instead a nice gain in torque...

[TopCatGr58]

Hey Aggie,

I thought some of the other real mechanics would have answered you, but I guess not?

If you don't have a hard copy of the service manual, you can download it from the website that Catatonic Bug provides in his profile. Then you can print out the Piston ring gaps specs and such. They should just need the pistons to determine the bore sizes. Don't know if they would be willing to check the ring end gaps after boring and adjust them for you?? They should also mark the pistons to match the holes, ie. 1,2,3,4 so you can keep them matched when you put it all together. Hopefully they will also chamfer/taper the bottom cylinder skirts to make it easier to put the jugs onto the pistons/rings.

The manual will also guide you in the assembly process, remember to stagger the gaps in the rings, and make sure you get the comp and other rings positioned right side up!

T.C.

[BA80]

The ring end gaps shouldn't be an issue with the piston kit. That's only something that needs to be watched when installing new rings on old pistons and cylinders. You can check it but they should fall into specs.

One thing I have noticed about the inexpensive bore kits is the pistons sometimes vary slightly in size. If yours do, have the machinist put the smaller ones in the center. The two center cylinders run the hottest because of airflow and the thicker the cylinder walls the more cooling you'll get.

Other than that it's pretty straight forward.

When you get the valves ground have the machinist dress the upper tips of the valves about 2 or 3 thousandths. Thicker shims are MUCH easier to find than thin ones.

[AggiesaurusRex]

Thanks guys! Also, just to check again, this is what the shop says they do
"Your cylinder will be bored and honed, each piston
will be hand fitted to it’s bore.
The piston to wall clearance will be set so that the two
inside bores (number 2 and 3) have .0002” more
clearance than the two outside bores.
They will be set up in this fashion as the two inside
bores will normally operate at a slightly higher
temperature.
The pistons will be identified by a small number 1
through 4 etched into the inside of the skirt on the
exhaust side at the bottom.
The pistons are numbered from left to right sitting on
the bike.
The ring end gap will be set at .004” per inch of bore
and the rings assembled on the pistons."
Sound right? I obviously should bring in a copy of the manuals stock specs for clearances and gaps, right?

[IanDMacDonald]

I'd be interested in hearing a price on that machine work.

[AggiesaurusRex]

He charges $150 for the work.

[IanDMacDonald]

WOW! My head work was close to $300 just to have valves installed, with lash set.