retro fit nikasil barrels on 79 R100?

[DucatiPete]

G'day,
My apologies if this has been cover elsewhere on the site, but I did a search couldn't find the info I was after.
I was hoping that post 81 (nikasil) pistons/barrels would bolt straight up to my pre-nikasil 79RS.
There's a pair going on that auction site and I suspect my engine needs at least rings (i suspect head work is also likely as there's smoking on throttle shut off). So I was hoping for a simple 'plug and play' solution.
Will the late model pistons fit the earlier heads (combustion chamber), without possible clearance issues?
A cursory search suggests I'm possibly asking a too complex question. Any fair opinions gladly welcome.
I'm guessing there'd be a drop in compression but I reckon I can live with that - might solve my persistent pinging problem?
What ya reckon?
Thanks
Pete

[Kurt in S.A.]

I kinda don't think so. Ted Porter sells the Siebenrock kits (Nikasil coated AFAIK) for the '77-80 models and another kit for the '81-84 models, so there's a difference. Something about an additional flange somewhere...maybe it can be machined off??

Kurt in S.A.

[DucatiPete]

The, albeit cursory, research I've done suggests the 81-83 barrels will directly fit the (later) earlier blocks.
I was more interested in how the piston-head nexus came together.
At this stage I reckon I'll buy em and see. If no go can always just on sell.

[DucatiPete]

I've found a few references in other locations re fitting nikasils to earlier engines.

After adding up the possibilities I'm pretty much going with the Bum's assessment:

"It is possible to install Nikasil cylinders on some pre-1981 engines. You have to trim a small amount of material at the bottom of the cylinder, inboard of the O-ring groove. You need the cylinder in a lathe to do this. This needs explanation, as there are two styles of Nikasil cylinders. The first versions, used between 1981 and 1984 were the same as the earlier cylinders, that is, they do not have a small step above the O-ring groove, and fit the earlier cases directly with no problems. LATER than 1984 Nikasil cylinders do not directly fit the pre-1981 cases, and you have to machine-off the step."

Here's hoping... I'll post my findings.

[motofly]

Bum's advice not withstanding, I did it to my 78 R100/7 and just used permatex gasket maker. The red goop. That was well over 10K miles ago and it's been just fine since. I don't recall everything that I had to do, frankly, but I don't recall having to do all that much to get it to fit. Can you get the matched pistons?

[DucatiPete]

It's a barrel/piston package. So will just need new rings.
I'm pretty sure the 79 engines have the same base o-ring arrangement as was used on the later nik cylinders (another transition year overlap).
According to the bum just a smear of sealant and new o-rings.