Rebore, hone or what?

Thinking of taking my std, pretty good shape bores, 1015 70.00mm block to 70.25mm. Should I seek a rebore, Hone, Crosshatch or some combination of two of the three?

Let's assume the bores are currently in good enough shape, to accept the original std pistons with new rings.

Thanks.

Measure and then decide what to do.
-Duck

Wear limit is strictly defined in manuals. Measure first, never assume. Measurement will make decision for you wether to go with honing and new rings or first overbore and new piston kit. I always thought honing and crosshatching where same thing.

Crosshatching is the result of a properly done honing operation, and not a separate process.
You need to measure the cylinder bore for wear and taper to determine if you can hone it and use stock size pistons, or whether it has to be bored to the next oversize (.010" or .25mm). If you bore the cylinder .25mm and use the stock size pistons, you are "Not" going to be happy with the result

Take the cylinder block to a motorcycle machinist and ask for their advice.

BH. To make a decision what to do, you need to measure the diameter of the pistons in the location specified in your manual which is generally below the holes for the piston pins. You need to measure your bores using tee gauges and a caliper. The bores need to be measured in several orientations and at various depths to determine if the bores are round. This is laid out in a service manual. In any case, the distance between teh bores and the pistons is called the cylinder to bore clearance. Over time and with miles, the cylinders get bigger and the pistons smaller. There is a limit as to how far the distance can be between the two and it is called the SERVICE LIMIT.

If your piston to cylinder clearance is within the service limit, take the block to a place that does machinework for bikes and get them to hones the cylinders... they basically rough them up in a pattern so new rings will seat. Honing should cost less than $20. You just need a set of new rings and off you go to the land of higher compression and speeding tickets....

If the clearance is OUTSIDE the service limit, you must bore the cylinders; that is, enlarge the openings and use larger pistons/rings. The amount of the bore will be determined by the size of the pistons to maintain a clearance under the service limit. If the guy who is going to do this job doesn't ask for your pistons, find another guy as each piston will be SLIGHTLY different and require slightly different diameter bores to maintain a consistent clearance. Boring costs $175-200 in most places now and combined with the piston kit you will need, makes oversized pistons a far more expensive option.

If you doubt you can make the accurate measurements necessary, remove your cylinder and pistons and take them to the bike machine shop and let them determine the clearances. You should know the max clearance (service spec) and don't rely on them to know what it is as they may have no documentation on your bike. Clearances tend to be quite a bit larger on older air cooled bikes than they are on modern water cooled bikes so DO NOT ASSUME this shop knows what the right numbers are.

To find this bike machine shop, call some service managers at dealerships in your area. I bet most of them use the SAME bike machine shop. DO NOT use a car shop... first of all, they will likely not have boring tools and hones that are small enough to work on your bike. Plus, they seldom have the knowledge required to work on bike specific machine shop issues.

If we were to do the .010" over pistons in a block, we wouldn't bother boring it, we would just power hone it out.
aperaceparts.com/shoptour.htm

Jay

Post edited by: APE Jay, at: 2006/01/24 17:13

Thanks everyone for the input. Spoke with the machine shop this afternoon who said they too would just hone, each pot to a specific piston/rings. $15/pot.

I am asking them to keep the piston/sleeve clearance as close to 1.7 thou as possible and the ring end clearance as close to 12 thou as possible. Obviously one will have some bearing one the other.

Any other guidance or things I should look out for would certainly be most appreciated. Thanks.

Whenever I go to the trouble of rebuilding a top end I bore and hone and install new pistons. I figure if I have it this far down why not spend the x-tra $. Then I know everything is new.

I agree. I'm going the new 70.25mm pistons/rings route.

Thanks again all the great input.

Sorry if this is thread hijacking but it is all on topic.

How many miles does a bike really need on it before the tolerance can be out? On a 650 in particular?

How do you know what rings to buy when the shop needs the new rings first to measure how much to bore and the tolerance etc? If you buy em first and find out you have to overbore that is $130 blown...

Any knowhow about this process is appreciated, and I hope your overbore and new pistons do the trick Barney!

It depends on things other than mileage, like oil change interval, how good a job the air filter does, and how the engine has been operated.

The machine shop dot't really need the rings to determine the bore size, it needs the pistons, and the bore needs to be measured prior to buying parts.

Post edited by: steell, at: 2006/01/26 12:54

I am going to be the odd man out here. I don't really think new pistons are necessary UNLESS they exceed the service limit OR are marginal for a personal rider. I generally keep a couple 903 blocks and several dozen used 903 pistons and with some measurement, I can put together a set that is within spec and will seal nicely without the expense of new pistons and boring. If you feel more comfortable using new pistons, I can certainly understand that but I think my money is better spent using NEW CAM CHAIN bits where I can. Those darn things have gotten more expensive than the pistons bwhahahaha... I WISH APE or one of the other big guys in the KZ game would come up with a CAM CHAIN KIT...

HD cam chain, idler assembly, bottom roller, front guide and the other top roller along with the rubber fingers (six of them) in a somewhat inexpensive kit. I would be willing to pay $200 for these things if they were good quality and designed as well as the stuff APE now sells.