Valve Stem Seals, or maybe throw in the towel

[Rijko]

btw +1 on new plugs and see if # 4 fouls bad again.
Could be blowby (compression loss - teaspoon of oil should raise compression temporarily)
Could be valve stem seal, quick or slow. In case slow could last a long time when cleaning/
replacing # 4 regularly.

[Rijko]

I'd do a compression test, preferrably a leakdown test too.
Maybe that will give you more info to go on when deciding whether to take the head off or not.

[unfocused]

What I see - 1&4 are running poor - 2&3 are running better but hot.
As mentioned - I'd replace all 4 plugs - retest.

Re-using any of those plugs is only asking for a misdiagnosis.

[Rich82GS750TZ]

Ed, plugs are D8EA per the owner's manual. Could you explain to a numpty what one step hotter plug I would look for? I'm thinking that tonight I'll wire brush 1-3 and put the new good spare D8EA in # 4. See how she runs.

There seems to be a variety of seals the right size on Ebay, mostly green in color, at quite a wide variety of prices. I'll look for the word Viton in the description.

[Nessism]

Looks like the plug fouled. I'd slam in some new plugs, one heat range hotter than what you have now, and see how she runs. If it runs good, keep riding, and always care a spare plug...

Since you have a spare head(s), I'd break them down for close inspection of the seats, valves, and valve guides. Use the best parts between the two, and use new valve stem seals. I like the newer viton type valve stem seals.

[Rich82GS750TZ]

That was going to be my next step. I keep a spare in my tank bag. Will put a new plug in that cylinder after work and report back. Thanks Rich.

[Cipher]

Pull the head. Ease of access and you get to readily check the crowns and beers.
also you need to inspect and possibly clean valves.

My money's on rings and blowby.

[rphillips]

If the thing just instantly lost power, that "may" have nothing to do with valve seals. First thing I'd try is determine why you lost this cyl. a new plug in that cyl. could possibly bring it back, and get you back to where you were before last Sat.

[Rich82GS750TZ]

I relayed in a post the other day my current woes with my GS750 T.

In a nutshell:
I’ve been burning oil since at least the start of summer. My guess is I need new valve stem seals. 20 miles into this first leg of a poker run this past Saturday, I was really hammering the throttle up a straight mountain incline. All of a sudden, I felt my bike’s engine power go sorta limp. Didn’t die. Kept running. Just became gutless. Great, just as I was getting into the most exciting part of the trip. I know this twisty mountain road like the back of my hand. Travelled it hundreds of times by car in my teens to get to work. I was about to leave the HDs In my dust or at least show them some great corner carving. Nope. It wasn’t meant to be. Bike was down on power. Taking off from stop signs became tricky, requiring much clutch feathering. The HD driver that was behind me said he saw white/blue smoke from my exhaust going up that hill.

I've pulled the plugs, here they are 1-4 L to R:




I hadn't looked at these plugs since I put them in new 2 years ago.
I wish I'd kept track of how much oil I've been using, but I haven't.

I started looking at plug color charts on the internets and there's too much for me to try to make sense of. I don't want to see any bickering on the matter. But I'm pretty sure # 4 is FUBAR.

Am I right in thinking that I need to replace my valve stem seals?

Cost of OEM seal 09289-05015 at partshark.com is $5.24 each = $83.84 + new valve cover gasket(was due for a clearance check anyway)

A source for just-as-good-but-cheaper seals and a part number would be appreciated.

Wondering if this can be done with the head in situ, my search yielded a "Rope Technique" that has been done on some 4-valve heads in place. It is my understanding that head-on valve stem replacement can be done, though I haven't yet found a thread where anyone did this on a 16-valve head.

With the improvised tools needed and the tight spaces, the risk of loosing keepers, etc, this looks like a job that would be easier tackled with the head on a work bench, Thinking some type of valve compression clamp may need to be purchased/borrowed/improvised.

Taking the head off also means the expense of new base and head gaskets, and a smattering of new copper washers.

Options:
1) Replace valve stem seals on this head, by whichever technique. This engine/head is from an '81 750E. This has different valve cover bolt arrangement than the original '82 engine.

2)I have the original '82 engine for this bike, which has 4 broken intake valve adjusters (see the destroy-rebuild link in my signature for gory details). I also have another head for this engine that I bought years ago for $30 on ebay. It looks intact. I should be able to build one good head from these pieces for the '82 engine.
I would not consider putting this head back together without also replacing the valve stem seals, even thought the engine didn't use oil when I took it out of service 3 years ago. They're 42 years old and probably pretty dried up by now.

I don't intend to get this done quickly. It will take me some time. I don't want to get rid of this bike. I have too much blood, sweat and tears invested.

In the interim, I am starting to look at the used bike market for something more modern/fuel injected, off-road capable.

Any helpful/experienced opinions on any of this is welcome. Thanks for reading.