Re plated cylinders.

[Neil Harvey]

Re plating Air-cooled Cylinders, assembler beware.

Recently we had an issue with some cylinders that were re plated for our customer.
Disclaimer, the company that did the re plating did a fine job with the work requested and the cylinders measure well. This has nothing to do with this company or any other plating company. I find no fault with their work.

It is a warning to all that before you fit your “newly” re plated cylinders, check the surface finish. It appears that this one supplier my customer paid for this service has an extremely wide standing specification with the plating company. They request using the roughness average number (Ra), an Ra of 15 – 25.

For those that may wonder why their engines smoked soon after re fitting newly re plated cylinders, this is probably the reason.

For matters of professionalism, I will not disclose the name of this supplier, this is just a warning to check before you fit. Do not take it for granted that the supplier knows what they are doing.

If you give a specification as wide as 15- 25, the person doing the honing who is in business and time is money, is going to stop at 25 and say job done. We have met the specification called out. But an Ra of 25 will destroy your rings and here is why.

Nikasil or any variant of nickel silicon carbide is extremely hard. This is why it’s used for liner coatings. It doesn’t wear much, so it has a long life. You cannot run an equally hard-faced ring pack as two hard surfaces hate one another. No chrome faced rings. A softer ring face is used. The heavy peaks left in the surface at 25Ra do not wear down. Your rings do.

Cross hatch and the ‘break in” period all came about with cast iron blocks and hard-faced rings. The rings wiped away the peaks and over a short period of time, the ring faces “polished the peaks down closer to the average mid-point between the peak and the valley of the cross hatch. The Rpk and Rvk. This is where the rings seal better as there is more surface for the rings to run against. But this is not how it works with these cylinders. The surface is too hard and the part that wears are your rings. The peaks remain, at their highest, the ring face wears and now you have poor sealing and poor oil control.

The surface finish for this type of coating must be lower, so that the “break in” is done in the honing process, not with the rings.

Be diligent and look at your re plated cylinders before fitting. Whoever you use to do this re plating, specify the finish you require along with a finished bore and tolerance.

[David Borden]

Neil, is it possible to have a light hone done to knock the tops of those sharp edges off if when checked you find they are on the higher end you're quoting?

[Neil Harvey]

Yes you can.

Its best to measure the roughness first, so you know how much to hone. And, you need to know the ID of the cylinder along with the piston clearance before honing. Expect to gain some clearance, hopefully a few 1/10's.

[Walt Fricke]

What Ra should a customer specify?

[Trackrash]

This subject comes up from time to time.

do I need to hone this?
do I need to hone this?

[Neil Harvey]

Aim for an RA of 6 - 8 with consideration as the honing process is in progress for roundness and taper with both under control along with overall ID size. This may be the limit to what you can achieve without adding too much clearance. It will all depend on how rough you are starting at.

Some cylinders I have seen require more re honing than others, so be careful. Do not induce a lot of temp when doing this as this is the death of the cylinder's integrity.

If this was done when originally plated, there would be no need for this re working. Its not the platers fault, they do as specified by the parts supplier and or the customer.