Nikasil coating scratches

I haven't been around much. This is due to not riding as a result of engine problems. I will put up a post soon with all the details. It will make interesting reading. Now to the current situation:

The engine has a total of 41 hours on it, and this time is being assembled with it's second crankshaft and third piston/liner set.

I inspect the new piston to see that the rings slide OK. I coat the piston and rings with fresh oil. I coat the liner and the assembly sleeve with oil. The assembly sleeve is made of bronze and has a tapered bore. The rings compress gradually as the piston is pushed through the sleeve into the liner. Only a slight thumb push is required to install the piston. I slide the piston down to the bottom of the liner ready for wrist pin installation.

I "time" the balancer when the crank/liner/piston assembly is put into the left engine case. The joint surface is coated with sealer and the right engine case is assembled. Everything goes together with no problems and I torque the case bolts.

I put more fresh oil around the piston above the top ring. The oil ring is still saturated from the initial assembly. I turn the flywheel back and forth multiple times to move the piston halfway up the bore and back down. It slides freely. After a few minutes I wipe the oil out of the bore. The rings are already marking the bore. Look at this picture in my gallery:

http://www.husaberg.org/index.php?full= ... _photo.php

Because the previous engine problems were due to nikasil failures, I'm not bolting the rest of the engine together until I'm sure the bore is fine. When I run my fingernail around the bore, it catches on some of the scratches you see in the photo.

I have to conclude that the Husaberg rings are too rough for the nicasil bore. Since the nikasil is extremely thin, any scratching will lead to an early failure. I am no stranger to engines and the Husaberg repair manual doesn't indicate that exotic procedures are need for engine assembly. Has anyone else run into this type of parts quality problem?

Some good suggestions. Scratches halfway are only because I had the piston moving halfway up the bore. I figured if there was to be some slight initial bedding, it might as well be at the bottom. These are all new genuine Husaberg parts. Nothing suspicious on the ring gaps. I always wash out a new liner with dish detergent and rinse well. This is standard practice to be sure it is clean. The stock coating seems unusually fragile but I suspect the rings to be at fault.

Ausberg,
I know what you mean about the chamfers at the bottom. They look good, but I found the corners where the bevels intersect to be rather sharp. I could work the rings into place from the bottom, but the large cut-outs would make this tricky. I machined the bronze installation sleeve to be about .0002 smaller than the bore and it works a charm. The rings don't catch at all going into the bore and the very slight taper (1 degree if I remember correctly) takes very little force to compress the rings. The Husaberg manual shows assembly from above as the normal method with a band style compressor.

I don't expect the bore to have a perfect appearance, but it should be just light witness marks, not enough to catch a fingernail on. I just can't see the liner standing up to normal use when it starts out like this. If there was some depth to the nickasil, I would hone it a bit, but it is so thin I'm reluctant to mess with it. The stock honing pattern looked good and should be fine for bedding the rings. There was no marking from the initial slide down the bore, it only started once I began oscillating the piston.

The whole theory is that the nikasil is hard enough that it doesn't get worn. The piston and rings are supposed to be the wearing parts.

Several months ago I made up a CAD drawing of the liner and set it to LA Sleeve for a quote. They came back with a price that was OK considering it would be a "one of" order. This was based on a fully finished cast iron sleeve as a drop in replacement. The extra weight would mean nothing to me as I'm only a casual trail rider. I may go ahead with this as I'm tired of all the bore issues. I would go with coated Athena piston for this.

I have attched the three drawings I sent to LA Sleeve. Dimensioned in Imperial (USA of course). As discussed with them, I would have to reduce the metric cutter radius dimensions to a similar closest imperial measurement. This slight change would have no effect on the use of the liner. I just added these files as a curiosity item for your entertainment.

EDIT: It looks as though they must be downloaded and opened. Didn't open directly on my computer.

As to liner ovality, "nsman" mentioned that the liners are clamped tight in the case. This makes sense but does not match up to what I have found. Without the orings installed, both sleeves that I had would slip down into the engine case when the clamping bolts were already tight. My measurements show that the liner is only supported by it's top flange and the oring squeeze. Reliable clamping would require very close tolerances and make the machining much more expensive.

They hadn't seen an engine constructed this way before, but because the size is large enough they can start with a heavy blank for an automobile engine. They said there should be no problem making this custom sleeve. The fellow I talked to who quotes the custom work didn't think there would be any tooling issues.

Apparently they do lots of work making sleeves for motorcycle engines. These are typically cold shrunk into the cylinder and finish machined by the bike shop.

http://www.lasleeve.com/master.html

Perhaps Thomas or Ben will add some thoughts on how tight the liner should fit in the cases.

Another question arises: Other than Hannes, have many of you run a hone through a nicasil bore? The hone I am familiar with is a 3 stone affair on a flex shaft. I doubt the multi-ball glazebreaker type would serve much purpose. The cross hatch pattern is usually the important goal.

Taffy,

Based on the 100mm bore:

LA Sleeve quoted the cast iron liner at $395.00 for one piece and $295.00 ea for two pieces (USD).

Dan at MotoXotica quoted $190.00 for the coated Athena/Wossner piston and $295.00 for a stock piston (USD).

He also quoted a stock liner at $390.00 but this was for the 95mm bore when I was considering other options.

These prices are 6 months old, so I called Dan to check and he said there is always some variation due to exchange rates and shipping charges. Although he is not an official Husaberg dealer now, he intends to continue supplying the Wossner parts.

As to the oil question, I feel that the full synthetic is a superior product. I can't say that it is truly necessary in these engines, but I like the way it clings to every surface and doesn't drain off no matter how long the engine sits. I also feel that nothing less than a top quality diesel oil should be used. As always frequent changes are the most important.

Piston expansion is something I am concerned about. I don't have enough engine experience to say what the tolerances "must" be. I tend to follow the manufacturer's instructions. I will say that the modern short skirt pistons do seem to cock off in the bore a lot. That alone might indicate close tolerances are a good idea. The Husaberg manual indicates a coated piston is run at tighter tolerances.

I wonder about the concept of coating a thin (somewhat flexible) sleeve with an extremely hard (rigid) coating. The difference between these materials must have some consequences. I think the extra rigidity of a typical cylinder will have advantages over the Husaberg sleeve.