Valve Stem Seals, or maybe throw in the towel

[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.

 

[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.

 

[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.

 

[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.

 

[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]

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.

 

[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.

 

[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.

 

[Rijko]

btw +1 on new plugs and see if [NODE="4"]# 4[/NODE] 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.

 

[Nessism]

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.

D7EA is hotter, which means the plug electrode itself will run hotter, which will help burn off any oil residue that collects on the plug. A hotter plug does not make the engine run hotter. The idea is to keep the plugs from fouling.

Those plugs look to have a lot of carbon on them, even down around the electrode where your wire brush won't reach. I'd get new plugs if you can...

 

[pdqford]

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.

Ditto on the compression/leakdown test. Listening at the dipstick hole would also give you some indication if no. 4 has a ring issue, or, more of a ring issue than the other cylinders.

When I first looked at the plug pictures, I thought no. 1 plug also looked marginal. Interestingly, both 1 and 4 are “outside” cylinders, AND are both fired by the Sam coil. When it went down on power was it misfiring? Continuing to nurse it along may have loaded up no 4? If no. 4 bridged, would that mess up the spark quality of the companion cylinder?

P.S. Valve stem seals are at their worst under high vacuum. As in deceleration. You weren’t backing off going up that hill so those HDs could keep you in sight, were you?

 

[rphillips]

If having to put a qt. of oil in with every tank of gas, yes, probably time to think of something more drastic. If a qt. of oil in 1000 mi., may get it back running like before last Sat. and be good to go again, like the past 2 yrs.... I've always been taught simplest easiest things FIRST... Wondering, do you have a guess on the oil consumption?

 

[Rich82GS750TZ]

Ditto on the compression/leakdown test. Listening at the dipstick hole would also give you some indication if no. 4 has a ring issue, or, more of a ring issue than the other cylinders.
I can't begin to understand how I could possibly know what I'd be listening for, but willing to learn. We can circle back to this concept.

P.S. Valve stem seals are at their worst under high vacuum. As in deceleration. You weren’t backing off going up that hill so those HDs could keep you in sight, were you?

No, not intentionally. This was at the start of about a 5 mile stretch of twisty roads with no turn-offs. I had intended to wait for them at the next stop sign. This is what I deserve, I guess.

If having to put a qt. of oil in with every tank of gas, yes, probably time to think of something more drastic. If a qt. of oil in 1000 mi., may get it back running like before last Sat. and be good to go again, like the past 2 yrs.... I've always been taught simplest easiest things FIRST... Wondering, do you have a guess on the oil consumption?

My best guess would be about a quart every 500 miles, roughly.

I will stop at the local Hardware store, MC shop, autoparts, places after work until I find D7EA plugs. Will put 4 new plugs in tonight and go for a 1/2 hour ride or so. See how it runs, Then pull plugs, take more pics and report.

I don't own a compression tester. Suppose I could look for one. I'm sure it's a useful tool to have. I don't have any friends that ride that would have one to borrow.
Recommendations on a Compression Tester with links would be appreciated if we think that's necessary at this point.

I'll have to read up on leak-down test. I have never done that before. But I'm open to anything really.

But that's getting ahead of myself a bit.

The power loss happened about 60 miles into the 250 mile ride. I'm sure I didn't do my bike any favors by completing the poker run when my bike was telling me to just head home.

​
Thank you all for the help so far.​

 

[rphillips]

Around here parts stores AutoZone, O'Rileys, Federated Auto Parts, will loan things like compression testers, you put down a deposit and when you bring it back undamaged, they give all your deposit back. Great deal for most folks, How often have you needed one within the past 10 yrs.

 

[Nessism]

500 miles/quart of oil is a lot.

I wouldn't bother with a compression or leak down test. I'd just plan on a teardown, and measure everything when it's apart. New rings, gaskets & seals, at a minimum.

 

[rphillips]

Funny how different folks are. No question do what said and all should be good.... Kind'f embarrassing, but my Honda CB1100F uses appx. qt. of oil every 3 or 4 tanks of gas, has been using oil since I got it, appx 20 yrs. ago, but usage has about doubled within those 20 yrs. Appx 6 yrs. ago it burned a couple of valves, due to lack of maintenance, had the head reworked and put it back on, hoping the new seals may help the oil thing. No, nothing changed, Of course, looking back, I should have gone through the whole thing but too late after it was back together. Still riding it like it is, just make a point to top off the oil while at home so none of my buddies see me, I don't want to put up with them poking at me about my old worn out Honda.

 

[93Bandit]

I will stop at the local Hardware store, MC shop, autoparts, places after work until I find D7EA plugs. Will put 4 new plugs in tonight and go for a 1/2 hour ride or so. See how it runs, Then pull plugs, take more pics and report.

I don't own a compression tester. Suppose I could look for one. I'm sure it's a useful tool to have. I don't have any friends that ride that would have one to borrow.
Recommendations on a Compression Tester with links would be appreciated if we think that's necessary at this point.

I agree with the others. Throw some fresh new plugs in and ride. Monitor oil consumption over a 1,000 mile period if you can. I wouldn't tear it down until you have an exact figure that warrants it. The plugs on my 850 look similar to yours, although not quite as bad. But I don't know how many miles you put on those plugs. I put about 7k miles on mine by the time they got that cruddy. I burn about a quart per 1,500 miles if I keep speeds below 70mph. If I ride the interstate at 80mph, I go through a quart per 800 miles.

As for compression tester, I bought this one years ago, probably 15 or so. I think I bought it at O'Reilly's, it was hanging on the pegboard behind the counter. I think I paid around $50 for it at that time, no idea what it costs today. I've been very happy with it, good enough quality for my needs. It's got adapters for most common plug threads and a couple adapters for hard to reach plugs. I've used it on cars, bikes, small engines etc. https://www.boschdiagnostics.com/products/professional-compression-tester

 

[Suzukian]

You can make your own compression tester by drilling out a spark plug from the plug wire connector end, all the way through till it comes out the other end. By using various hoses till you get to the right thickness, you buy a cheap pressure gauge that goes up to 200 lbs., and voila, you have a compression tester for maybe $15 bucks. if you use a Harbor Freight gauge. You just need one to tell you relevant pressures between the cylinders.

 

[Eli69]

Rich, I sorta remember seeing a bit of smoke last time we were riding. Compression tester is a very good tool to have. Helps you figure out if you need valve stuff or ring stuff. I'd get one.

 

[Baatfam]

Rich, I have a Craftsman compression tester, (#47089 if you want to google it).
Send me a PM if you want to borrow it. We'll have to check on shipping each way, but otherwise it's yours to use.