1980 GS1100ET pistons/moly coating question

[jb1k]

Hello, Merry Christmas to all...

I am in the process of doing a top end on a GS1100 ET. I bought this bike ($3k/10k miles indicated), seemingly straight and solid, albeit a bit faded and down on power, attributed to CV carbs with pod filters, running rich. That was the first thing I dealt with. (And in my parts hoard I found a GS1000 airbox from way back when, shared with this bike, thumbsup.....)

Opening up for valve service, I found that the motor had been molested, 15 aluminum retainers and one OEM steel, cams in bad shape, so it came apart.
All new valvetrain components have been sourced, found some high volume oil pump gears along with a lockhart cooler and the head is at EdCo in Petaluma California.

Bore is stock, cylinder nice (although it would appear it sat for some time), ring end gaps measured ~.010-.012", well within spec. I was planning on honing it myself. (new OEM rings in hand)
But I realized today during parts cleanup and inspection that these pistons were coated from the factory. The coating is uniformly gone from all the pistons except in the wristpin region. Otherwise they look pristine.
Can anybody tell me if this is a problem for these motors? The coating seemingly very thin, thinner than the armorglide on the latest wiseco (and other) pistons.

And an internet search doesn't reveal any info on the (GS coating) subject. Or the armorglide for that matter.
Any info and real world experience appreciated. Seems like it shouldn't be a problem with modern oils, high volume gears, and a cooler.
Not thrilled at the prospect of throwing another >$1000 at it.


And if anyone is looking for a Martek440 ignition, free to a good home...

[Nessism]

The stock pistons were not coated. Can you post up some photos?

You might want to measure out of round, taper, and piston to wall clearance. No more than .0010" out of round or taper allowed. Piston to wall clearance is less important; the manual states that .0047" is the service limit. As long as the specs fall inside these numbers, I'd run the engine, regardless of piston coating.

[jb1k]

thank you for the reply, and see the attached. the gentleman who sold me the GS750 gears and oil cooler mentioned this in passing as we discussed other aspects of my build. but he recalled that it was on later models only..
I will take some measurements this afternoon. but the original finish on the piston is still discernable.

[Nessism]

I stand corrected. Here are some stock 1100 pistons that are coated...https://www.ebay.com/itm/393419200174

I think the coating is largely for break-in. I still say if the pistons and cylinder measure in spec, I'd run them.

[jb1k]

Thank you. Some improved measuring tools en route, but my inside micrometer tells me the bores are round and well within spec, Ring gauge to verify its accuracy coming, and the pistons will be double checked when the 2-3 micrometer arrives. And ring groove widths are spot on.
It was also suggested that a feeler gauge can also be used with a naked piston inserted in the bore. A new one on me, will explore that tomorrow...

And I saw those ebay pistons, tempted, but not wanting to spend.

[Suzukian]

I agree with Nessism about the coatings being for break in. With only 10K miles on it, unless he ran it out of oil, I wouldn't think the bottom end would even be an issue. Best of luck and many miles.