TOPIC: Top-End Redo

Not sure if this is a smart question or not, but here it is regardless...

In the long run, how much better to install a cylinder block with new sleeves, versus honing the old ones when the bores are worn but still within spec?

Ideally, there should be no out of round or taper in the bores, and the piston to wall clearance would be to the low end of the spec. Personally, if I were rebuilding an engine and longevity was the goal I'd try to find some OEM OS pistons and then have a good company like APE do the cylinder boring/honing work.

I re-did one of my Z1B's. The cylinders had been bored to 1015 cc but I wanted to go back to 903. I had two choices...new sleeves or used cylinders. I went with used cylinders that were within spec and only required honing because it was a cheaper alternative. I only put a couple of thousand miles on each of my bikes each year so the used cylinders will last my lifetime.

We're really talking only about the 80+/- mm length of cylinder surface where the rings travel, correct?
Short video explains basically what is going on in there:

A cylinder sleeve got the most wear on the TDC and BDC area. The piston rings residence time is much longer( slow piston speed) in this area.

Cylinders do not wear evenly over time. The high cylinder pressures near the top, combined with large temperature variations over the entire cylinder, ESPECIALLY on air cooled cylinders, make the bore wear far away from round and true. Honing ONLY does not return these out of round bores to round. A good Sunnen type hone will do ok, but there is flex and stone pressure changes that do not allow it to re true the bore to round. Add to this the point that the piston to cylinder clearance will now be far greater than the specs call for. The ONLY way to return the bores to round is a machine type boring bar, or mill with boring head, but the boring bar is better, and then hone. That then requires the cylinder to be increased to the next oversize.

daveo wrote: We're really talking only about the 80+/- mm length of cylinder surface where the rings travel, correct?
Short video explains basically what is going on in there:

Sorry but only 66mm stoke on these engines.

I'd think about APE too..... pretty sure they have a Wiesco 1170 set with 10 and a 1/4 to 1. With your carbs bet that thing would be a real beast.

zed1015 wrote:

daveo wrote: We're really talking only about the 80+/- mm length of cylinder surface where the rings travel, correct?
Short video explains basically what is going on in there:

Sorry but only 66mm stoke on these engines.

I thought the distance between the top and bottom piston ring would be added to the stroke to determine the total ring movement (wear area) in the cylinder.
If I am mistaken, oh well...it's not my first or last.

KZB2 650 wrote: I'd think about APE too..... pretty sure they have a Wiesco 1170 set with 10 and a 1/4 to 1. With your carbs bet that thing would be a real beast.

With lower compression the engine runs well on Regular gas. It operates cool and should last a long time. I may bump the compression up a little, but prefer to keep it close to stock. Would be the third top-end redo since I've owned her, and I hesitate to add more stress than she might be able to handle.

True. A lot of folks believe raising the compression ratio will give them lots more horsepower, but that really isn't the case unless other engine modes are performed. The links below show the effect on hp as compression ratios are increased. Ed

www.wallaceracing.com/hp-cr-chg.php
www.bgsoflex.com/crchange.html

650ed wrote: True. A lot of folks believe raising the compression ratio will give them lots more horsepower, but that really isn't the case unless other engine modes are performed. The links below show the effect on hp as compression ratios are increased. Ed

www.wallaceracing.com/hp-cr-chg.php
www.bgsoflex.com/crchange.html

Thanks for posting that great piece of information!