IMD Pistons

[muskrat]

G'day Fellas.
This is the type of split skirt pistons I used on the first rebuild of the A7 plunger back in the early 80's. They nipped up but didn't brake after an hour sitting on 70mph  . I used the recommended 1,1/2 thou clearance.
Cheers

[Triton Thrasher]

G'day Fellas.
This is the type of split skirt pistons I used on the first rebuild of the A7 plunger back in the early 80's. They nipped up but didn't brake after an hour sitting on 70mph  . I used the recommended 1,1/2 thou clearance.
Cheers

0.0015” wasn’t enough that day.

Gratuitous chamber of horrors photo:

[Colsbeeza]

Hi Miker,
I have written out the method of getting the IMD circlips fitted which worked for me.
Scott & Jay - Can you steer me to Klaus's method of bedding the rings?  Is that a "dry" method ?
Col

[Greybeard]

Hi Miker,
I have written out the method of getting the IMD circlips fitted which worked for me.
Scott & Jay - Can you steer me to Klaus's method of bedding the rings?  Is that a "dry" method ?
Col

You forgot to add the bit about finding the clip after it went on a trip of the darkest corners of your workshop!   

[Triton Thrasher]

You forgot to add the bit about finding the clip after it went on a trip of the darkest corners of your workshop!   

I revel in the luxury of spare circlips before I start fitting pistons, these days.

[Colsbeeza]

Yes GB that was my greatest fear. I had no spares.
Sweating profusely until the last circlip was in.!
Col

[Colsbeeza]

Attached Data from my Crank Balance in 2019 for the Golden Flash as promised. Sorry I had to save it in pdf format to get it to attach. My Spreadsheet is in xlxs format. How do I change this to an acceptable format?
IMD and Hepolite Piston weights are detailed. The IMD are considerably lighter, which suited me fine, as I already had too many holes drilled in the flywheel and Balance Factor with the Hepolites would have been higher than I wanted.
The IMD's gave me BF = 59.  (Note 54 for standard, 65+ for racing)
Note - mentioned are Priory Gudgeon Pins (from Priory Magnetos) with the Hepolite Pistons. I had purchased them in the hope that I could re-use the old Hepolites as the old Hepolite Gudgeons had been badly damaged by some ham-fisted operator, so calculated the BF with Priory Gudgeons - not used obviously.
The quality of the IMDs is impressive, and the clearances are spot-on. Hair Dryer used to get the gudgeons to slide into the pistons nicely - no go without heat. Even used the hair dryer to install the gudgeons in the small ends. They would go in without heat, but would have needed some light tapping.
Cheers
Col

[groily]

That is great info, thanks. (Not that I am taking things apart to weigh it all or change the BF on mine. It will be what it is, and I'll avoid running in any rough patch caused by the change in piston weights, if there is one.)
I second your comments on clearances - my experience is the same.
Only gripe  . . . those circlips!

[Triton Thrasher]

Hair Dryer used to get the gudgeons to slide into the pistons nicely - no go without heat. Even used the hair dryer to install the gudgeons in the small ends. They would go in without heat, but would have needed some light tapping.

I’d be happier with small ends that are free to swivel on a cold morning.

[Colsbeeza]

Yes TT, I decided to leave well enough alone, and hope the high spots will ease quickly. Besides, if it is that cold, I'll stay in bed.
Col

[Jules]

couple of questions then...
1. whats wrong with the old style circlips with the wire tab? has anybody really ever experienced them letting go?
2. after fitting the new IMD circlips, I guess you never want to (try to) take them out again, lol.....

[Triton Thrasher]

couple of questions then...
1. whats wrong with the old style circlips with the wire tab? has anybody really ever experienced them letting go?

Not me, but this stupid thing, not from IMD, isn’t even round. The flat bit next to the bend didn’t sit down in the groove.

2. after fitting the new IMD circlips, I guess you never want to (try to) take them out again, lol.....

Use a pointed tool to rotate the circlip, so it crosses the slot at the bottom.  Then use long-nosed pliers.

[Colsbeeza]

I doubt that you could rotate the IMD circlip - they are so hard and very tight in the groove. The IMD circlip has thicker wire (1.38mm) than others. I did not want to use an alternative with thinner wire, as I was concerned that it may move about in the IMD groove and eventually come out.??
TT - In Scotland, you might be concerned that the gudgeons might tighten in the small end on cold mornings. Here in Oz, I doubt I'd be riding in under 15 deg C. And I've never seen snow here. More concerned about overheating in 40 Deg.
Anyway if it seizes I'll know why.!
Col

[chaterlea25]

Hi All,
In my opinion those circlips as posted by TT are crap 
Circlips like these were supplied with the new "Hepolite" pistons I got for a current build
I threw them away and use plain clips without the "ears"
The wire circlips in service should be pushed tighter into the groove by the little chamfer on the end of the gudgeon pin , the ear on the clip prevents this happening ..
Some time ago there were a lot of circlip failures on vintage Indian and HD engines where the clips with ears made a bid for freedom 

John

[berger]

apart from 1001 things what does IMD stand for , as in the piston makers