IMD Pistons

[RDfella]

Keith - it's where the circlips go when trying to fit them - 'in many directions'.

[berger]

RD fella   

[Colsbeeza]

After several hundred miles on the IMD pistons, I was expecting that the kick starting would get easier.
But no chance!! - I went for another Club ride on Saturday 28th, and a few members were blown away by the compression. I always try to kick start after one of the pistons has passed over the compression stroke. I can stand with my full 78Kg on the kickstart lever with full weight, and it takes about 15 seconds for the piston to go over.
My kick start lever is 10-15mm shorter than standard, and is of unknown pedigree (see image), as it came with the bike 40 years ago.
One of the Super Rocket owners asked me about the pistons, and surmised that the 3-piece oil rings essentially negated the ring gaps, making it nearly impossible to allow enough gas to leak past the rings. One would think a 325cc piston would not be so hard to kick over.
Technically, pistons are 7.25 : 1 on first overbore, bores honed and plateaued to 500 grit (essentially run-in immediately), Top ring is silver coated Moly steel, second black ring is uncoated ductile iron, oil rings are two chrome steel thin rings with expander between. I checked all ring gaps were at 12''' when installed. Never burnt a drop of oil since.
Anyone with chrome/moly rings experience the same thing.?? Anyone got a 2-foot kick lever?. Can I get a decompressor for each cylinder?
Col

[berger]

col i made a steel block to fit on the kicker shaft and fitted a longer japanese bike kickstart lever, works a treat

[Triton Thrasher]

The good compression should make it lively.

[muskrat]

G'day Col.
Sounds like me (70kg) trying to kick over the 10.5+:1 Cafe.
Do you have a pic of the pistons? Also what rods are in it?
The Cafe has 10.5:1 pistons plus R&R rods that are a bit longer than std.
Cheers

[Colsbeeza]

Hi Muskrat,
Their website has a picture.
                     https://imdpistons.com/products/bsa-a10-piston-kits
They advertise only +.20 and +.40, and I think only 7.25 : 1.
However, I'd contact Andrew Wright and ask what he can supply. He was very helpful for me.
I paid UK95.99 pounds/pair back then but are now 119 pounds/pair.
I have the original standard rods which came with the bike, probably from new.
Yes TT it has great torque, and feels good. Thanks Berger, no-one has offered me a 2-foot lever yet.
Col

[Minto]

Hey Musky, here’s a pic of my IMD pistons, pins and clips on the kitchen scales before fitting.
The ones I took out were 671 grams.

[Minto]

And on the rods.

[mikeb]

hi Col. something weird there. i find my super rocket no harder and possibly easier to kick over with the standard 7.25:1 IMD's compared to the old +80 8:1 JPs. And it hasn't burnt a drop of oil since and the oil stays green for ages. Happy customer.
But with the lower comp it does lack a bit of punch off the lights

[Colsbeeza]

Hi mikeb, I agree it is odd. But further to this, I also got a head job. - No not that kind - New valves, guides, seats re-cut etc so no opportunity for leakage.
My oil also hasn't coloured - I read an opinion that cast iron rings and #150 hone generates a lot of iron dust - the kind that is magnetic on the sump plug, and reduced engine life significantly. The argument for a fine hone and chrome etc rings is that it doesn't generate metal dust. I think this is why the oil hasn't coloured yet.
I am happy with the punch, haven't tried to drag anyone at the lights yet.
Col

[mikeb]

Col - i recall another NZ forum member had greatly increased resistance to kickstarting his b33 when adding 3 piece oil rings, whereas my b33 with the same 3-peice oil rings (from a mazda cx3) was no harder to kick at all. these rings were iron not chrome (i thought chrome takes ages to bed in on our old bikes). i wonder if my coarser grit ham-fisted honing skills are an advantage in this regard?

[Colsbeeza]

Mikeb,
Yes the combination of ring metal and hone grit size seems to be a big factor.
As I understand, cast iron rings in iron bores wear fairly fast in early running hours and need a coarse hone to bed in. Traditionally our bikes were ground to about #150. Steel or chrome rings may never bed in properly with such a coarse grit. I believe other IMD customers find no oil consumption and no smoke from very early. They have to seal almost immediately, so the very fine hone simulates a run-in bore. You couldn't do this on a worn bore.
Some weird things happen - I purchased a new Chrysler Sigma in 1980, and it burnt oil from the very beginning. I was topping up the oil between oil changes, and it was black as the ace of spades. The factory said normal consumption (BS). They had chrome rings and Nikasil bores. After 180,000Km, I got sick of it.  The bores still had honing marks left there from new. I took some advice and honed the bores to remove the glaze and installed cast iron rings. It never burnt oil after that. And all up cost for rings and new bigend slippers was A$140 in the 1980's.
Col

[RDfella]

Some early car / truck engines had chrome plated bores. Later, chrome liners in diesels were the fashion. Rule was chrome rings in a cast iron bore, cast (or steel) rings in a chrome bore. I always preferred the chrome rings in cast iron. I guess a nikasil bore must be similar to a chrome one, so chrome rings a no-no in those as they'll never bed in.

[Colsbeeza]

Hi RD,
I got this from a website:-
Nikasil (an abbreviation of nickel silicon-carbide) is an electroplated composite coating comprising of a nickel matrix holding silicon carbide particles in place (similar to rocks and cement in concrete). The surface nickel is honed or machined away, exposing the silicon carbine which provides a very hard surface for the piston rings to run on.
Yes harder than chrome apparently.
Col