Best way to fit 1000cc Nicasil to early R90/6 cases?

[Sam LP]

Hello All

My 1974 R90/6 has the original iron sleeved cylinders. The pistons are at +1. I would like to soon fit 1000cc Nicasil barrels with some after-market Mahle pistons from Motoren Israel.

I know that the barrel holes in the cases are too small for these Nicasil cylinders. I bet there are ways to work around this. I can imagine some of the complications and benefits of either of these methods, but would be very interested to hear your thoughts.

What would be the best way to fit these barrels?:

1:Turn the barrel bases down to fit

2:Open up the holes in the cases?

Finally: What are your thoughts on using 2nd hand barrels?

Thanks, Sam

[Max Headroom]

Sam, turning the barrel spigot down to 97mm will leave the wall thickness virtually non-existent. They will be only 1.5mm thick after machining, and will probably crack shortly after startup. R80 Nicasil barrels have more material to work with and respond better to machining the spigots, but not the R100.

Machining the counterbores in the case would be fine, although it would require stripping the engine completely. You might find it cheaper and easier to swap your engine internals into a later crankcase if you're prepared to go down this path. The post '81 cases have a better crankcase breather configuration, and a slightly better lubrication path too, which gives priority to the front main-bearing instead of the front cam bearing.

As for using 2nd hand barrels, I'd have no hesitation providing they are within spec and devoid of gouges or surface damage.

My $0.02c

[Sam LP]

Thanks Max Headroom
What you say makes sense. One of my problems is that I have a sentimental attachment to my crankcase, the number matches the frame and I have already gone against the advice of the engine tuner Jim Cray by keeping it. I will investigate the cost of machining the counterbores, but in respect of your advice will also find out what it would cost to have my engine internals transferred to a used crankcase.
Thanks,
Sam

[Garnet]

SIEBENROCK makes a 1000cc upgrade kit for early small spigot cases. Motobins used to carry it but I don't see it on their site right now.

Email them and see what they have to say.

I have a set of small spigot R90 iron jugs bored to take STD R100 pistons. There is not a lot of meat left on the spigot.

[Major Softie]

As soon as I started reading your question, I immediately went to the same place as Max - a lot easier, more satisfying, and probably cheaper to just trade out the motor.

I too hate to lose matching numbers if I don't have to, but then, I hate to toss out old parts. I suggest you keep the matching numbers engine and make it a long term project (preferably one that does not involve hogging out the holes, but that would be my personal preference). Perhaps you'd like to make it all perfect and like new. Perhaps you'd like to hot rod it with cams, flowed heads, etc.. Perhaps you'd like to turn it into picture perfect livingroom art. Lots of possibilities.

[Sam LP]

Thanks for your help and suggestions. I'm starting to come around on this. Would a post '81 R65 crankcase be a possible candidate? I have one of those. Or are the counterbores too small? Sam

[Max Headroom]

Thanks for your help and suggestions. I'm starting to come around on this. Would a post '81 R65 crankcase be a possible candidate? I have one of those. Or are the counterbores too small? Sam

The R65 crankcase differs in one key area - the angle of the cam followers. Due to the shorter crank stroke, the barrels are shorter and the cam follower/pushrod angle is correspondingly steeper. You may encounter problems using an R65 crankcase for this reason. Also, according to one of the airhead books I read (maybe Andy Schweitzer?) it was mentioned that the R65 crankcase was slightly lighter than the Type 247, which may mean that it's not quite as strong. That's something which would be harder to verify without checking 247 and 248 crankcases side by side, but something to be aware of.

[Ken in Oklahoma]

As soon as I started reading your question, I immediately went to the same place as Max - a lot easier, more satisfying, and probably cheaper to just trade out the motor.

I too hate to lose matching numbers if I don't have to, but then, I hate to toss out old parts. I suggest you keep the matching numbers engine and make it a long term project (preferably one that does not involve hogging out the holes, but that would be my personal preference). Perhaps you'd like to make it all perfect and like new. Perhaps you'd like to hot rod it with cams, flowed heads, etc.. Perhaps you'd like to turn it into picture perfect livingroom art. Lots of possibilities.

As I was reading down the responses I was already phrasing in my mind essentially the same advice the Major gave. So I'll just give it a hearty +1 and post my plan B advice.

Buy a whole other bike! Airheads are still relatively available and relatively cheap. Just go to the IBMWR want ads and sometimes eBay and look around. (Well maybe you want to wait going to IBMWR until after they get their problems sorted out.)

A guy really does need a spare airhead! (Now who would've thought that would be my plan B?) Airheads age going to be down somewhat regularly for maintenance, or maybe even a mod, so having a "spare" takes some of the urgency away from getting the bike back on the road.

More power is really nice and it has a Siren pull. I'm a big fan of more power. Yet, on the too rare occasions when I jump on the R75/6 that I keep in Idaho my first reaction is what's wrong with this bike? And then within a second or two I remind myself that it's a 750. They have less power.

The thing is, when I take the R75 on a ride along with other more powerful bikes I have to kind of wring it's neck, so to speak, to keep up. That's fun of another type. I have to sharpen up a bit, make my gear selections more intelligently to stay in the power band, and generally pay more attention to driving the thing. And when the time comes, it's easy enough to spool down and simply enjoy the smells and sights of the road.

At the end of the day I've had just as much fun as I would on a R100.



Ken

[mattcfish]

I've been contemplating this as well. I have a 1975 R90 that seems to have the last small spigot block ever made (manufactured in Sept 1975). I don't want to bore out the block at this point.
First question, can an iron cylinder be given the "Nicasil" coating?
2nd, I noticed that the Siebenrock 1070cc kit doesn't have spigots on the barrels. They are flush on the bottom. At least the picture in my catalog doesn't show them. It uses pistons with very short skirts. How do they keep the barrels in alignment with this set up?


I guess what I'm getting at is...would it be possible to use 1000cc Nicasils with the spigot cut off and modified, short skirt, pistons on a pre-1976 block?

[mattcfish]

SIEBENROCK makes a 1000cc upgrade kit for early small spigot cases. Motobins used to carry it but I don't see it on their site right now.

Email them and see what they have to say.

I have a set of small spigot R90 iron jugs bored to take STD R100 pistons. There is not a lot of meat left on the spigot.

The Siebenrock kit still requires that you bore out the block.