Bore or Hone Advice

[hudson]

Thanks Melville! I talked with Eddie at Boxer2Valve. Appreciate the advice. If .5mm doesn't cut it, does the OS graduate in small increments thereafter, or does it just double? Assuming more than .5mm is not enough, at what measurement spec would I need to consider larger pistons? Having it bored with replacement rings obviously is more ideal than having to add pistons in the mix.

Does anyone know an average/reasonable price to do both bores and possibly replace the pushrod tubes (they are slightly rusty in spots but not terrible. I figure it may be practical so I don't have to re-pull it all of sooner rather than later)?

[Kurt in S.A.]

There are no in between bore diameters. It goes up by 0.5mm increments. Even at the 1st overbore (0.5mm) you're going to need new pistons and rings...the spacing between the piston skirts and cylinder walls become too big.

Kurt in S.A.

[hudson]

Ok. I wasn't sure. this confirms it. I am planning on taking it to Boxer2valve. Thanks again all!

[George Ryals]

How do you get a circumferential scratch??? Cylinder scratches are usually longitudinal, caused by a broken ring or a chunk of carbon riding up and down with the piston. Looks like a crack to me.

[hudson]

George - if that is case, I assume it would have to be re-sleeved? Even if reboring could take it out, would it be cheaper to resleeve to original specs anyway and keep my original pistons? If this was possible, I guess I only have to do the one cylinder since the other seems to be ok? Not sure if this is even an option or not or even economical? Just figure I'd ask.

[hudson]

doing some more digging, I don't see these as resleeving and even if so, a big job. so just chance reboring doesn't work out so the upsized pistons are not usable, , I probably need to buy the 1000cc kit.

[Seth]

Another option:
Have the cylinders plated like the factory Nicasil
When I had some heads done by Ted Porter, he recommended it
And recommended 2 shops. One in the mid-west. The other in PA.
PowerSeal USA.
If your pistons are still good, they may be able to reuse.
You’ll need rings that are compatible with the plated cylinders.
Ted sells them. The results are better than original.
Check into it.

[Rob Frankham]

The blemish on the cylinder would appear, in my opinion, to be caused by corrosion, probably caused by the vehicle being laid up and water (condensation?) settling in the cylinder against the rings.

From the photos, it is definitely beyond honing.

The first step is to measure the existing bore and see whether the cylinder is suitable for rebore. If it is, you will need the rebore, new pistons and new rings. You cannot use the existing pistons or rings in a rebored cylinder.

Rebores go in set stages to suit available pistons. You might be able to source non OEM pistons of different sizes but that's a whole different ball game.

This won't be cheap but, unless you are very lucky in sourcing repacement parts, it will be the cheapest way to address the problem.

Dependent on budget, it is a good idea to do both cylinders at the same time for several reasons including the fact that the two replacement pistons can be balanced and balancing the engine output with one worn and one unworn cylinder might be problematical.

Talk to the reborer before going any further. He will be able to advise on te best way forward. A bike orientated shop will probably supply pistons and rings with the job, a generic engine rebuilder will do just as good a job but may ask you to source pistons and rings yourself. This is often a cheaper way to go.

Reboring the cylinders will not make an appreciable difference to the engine capacity.

If the cylinder isn't fit for boring, the most economical approach is likely to be sourcing a replacement second hand. Obviously you need to balance the risks and costs between buying from a private seller or a dealer.

Rob

[Rob Frankham]

Another option:
Have the cylinders plated like the factory Nicasil
When I had some heads done by Ted Porter, he recommended it
And recommended 2 shops. One in the mid-west. The other in PA.
PowerSeal USA.
If your pistons are still good, they may be able to reuse.
You’ll need rings that are compatible with the plated cylinders.
Ted sells them. The results are better than original.
Check into it.

Nikasil isn't a real option here. The Nikasil coating is microns thick and complies with the contours it is applied to... or to put it another way, the problem would still be there. The cylinder would have to be rebored anyway.

Rob

[Roy Gavin]

Boring out a cylinder with a cast in Alfin liner for a pressed in liner is not much of and Idea either as the new liner usually has a larger OD than the thickness of the Alfin finned iron sleeve, between the fins.
Cheapest way is probably to try and find one secondhand cylinder, and fit the existing pistons with new rings.
Motorworks in England could probably help with the cylinder and rings, and they may even know the correct grade of hone to freshen up the bores, I dont think it is 240.
German Ebay is also a good source of parts and most dealers will ship overseas.