Valve Stem Seals, or maybe throw in the towel

[KiwiAlfa156]

Just my 2 cents worth as the owner of a GS650 that is drinking oil and smoking a little on cold start up and when being ridden hard. I restored it about 3 years ago and dismantled the top end and barrels. The ports tidied up, new valve seals, valves and seats redone, everything measured and reassembled. I (mistakenly it turns out) gave the barrel a hone and didn't replace the rings. After running in the engine, all four pots showed excellent compression but oil consumption wasn't good and hasn't improved. The engine makes really good power. I pulled the plugs and they looked a lot like yours with a crust of ash (but no carbon fouling) on all 4 plugs from burning oil. My theory is that the hone has seated the compression rings which had enough meat on them, but wore out the oil control rings which may be did not. It got fresh viton valve stem seals, so the likelihood of it being stem seal related is slim. It smokes on cold start up which according to the 'internet' is a classic sign of worn stem seals... although badly functioning oil control rings and the bigger clearance of cold motor might, to my mind, yield the same results. Compression and leak-down testing will give you some clues on the state of your compression rings and valve seats, but won't tell you anything about the oil control rings. I'm on the cusp of ordering fresh rings and gaskets.

 

[Rich82GS750TZ]

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.

Yeah, I’ve been on borrowed time.

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.

Thanks, Bob. I’ll consider it. Harbor freight has a few that are reasonably priced. But how do I know if they have the right adapter to fit the threaded hole in my intake port?
https://www.harborfreight.com/quick-connect-compression-tester-62622.html?utm_source=google&utm_medium=cpc&utm_ca mpaign=12144811130&campaignid=12144811130&utm_cont ent=117789278878&adsetid=117789278878&product=6262 2&store=830&gclid=CjwKCAjw6p-oBhAYEiwAgg2PguHcessS93VmR_aMK6M15_UoBG_tUWHOA4WvI dibSC-W1vCdkNeAIRoCcakQAvD_BwE

I just put in 4 new B7EA plugs, went for a 1/2 hour ride. No change. Here’s a video of what she sounds like. After the bike cools down I’ll pull the plugs and post a pic. I think it’s just about beer:30.

 

[Baatfam]

Thanks, Bob. I’ll consider it. Harbor freight has a few that are reasonably priced. But how do I know if they have the right adapter to fit the threaded hole in my intake port?

There is really nothing special about the Suzuki spark plug threads, as far as I know, but you can google it.
The craftsman kit has covered everything I've tried it on.

 

[KiwiAlfa156]

Sounds like its running on three cylinders. Check the temp of the header pipes.

 

[Rich82GS750TZ]

Sounds like it’s running on three cylinders. Check the temp of the header pipes.

Agreed. I have no way currently to measure the actual temperature. # 4 is hot, but not as hot as the other 3.

 

[Nessism]

Check from a cold start. Very carefully touch the headers right after a cold start. You should be able to quickly figure out if number 4 isn't firing... If it isn't, visually check spark next, with the plug held against the engine.

 

[Rich82GS750TZ]

Ed, before installing the new plugs, I did check spark on each against the head. All 4 sparked.

After my first cold startup with the fresh new plugs shown in the video above, only running for the 3 minutes of the video, I touched each header pipe at the top bend. # 4 was hot but I could keep my thinly gloved hand on it for a few seconds at least. 1-3 were much hotter in comparison. I could touch them but but only very briefly.

Here’s the new plugs after 1/2 hour ride.

Close-up of # 4

 

[KiwiAlfa156]

Check the carb diaphragm on number 4. I'm having something similar on the 750 Kat and I've discovered some holes in mine. I was doing a WFO main jet plug chop and it suddenly felt like something 'gave' and the performance degraded somewhat, which sounds very much what you describe in your OP. Anyway the story is all here https://www.thegsresources.com/_for...t/1729318-fiddling-the-mikunis-on-the-kat-750

 

[Rich82GS750TZ]

Interesting. Hmm, tomorrow evening I’ll take the lid off # 4 carb and inspect the diaphragm.

 

[Redman]

Rich,
I suggest when checking the exhaust header pipe temperatures, do it about 3/4 minute after cold start up, and again after a couple minutes, before the head and cylinders heat up.
Oh, and just tap the pipes with back of fingers (skin is thinner on back of fingers, if use finger tips the skin is thicker there and delays your detection and then skin is already heated up oww oww. Old boiler operator guy taught me that decades ago.).

That is all I got to help.

(I was expecting new plugs to clear up the symptoms.)

 

[2BRacing]

Just my 2c here in the hope that there may be an easier solution than remove/replace cylinder head to replace seals: plug number 1 also looks fouled, but certainly not as much as number 4.

Have you closely inspected electrical connectors and measured voltages and resistance values at the coil feeding 1 and 4? Also plug wire and cap of number 4. Plugs 2 and 3 look OK, but if valve stem seals are the culprit, I would expect all the seals to be similarly worn (causing all plugs to be fouled), and not just seals badly worn on 4 and slightly worn on 1.

My first guess is therefore an electrical issue on 1 / 4 side.

 

[Rich82GS750TZ]

I will measure coils this evening. Thanks.

 

[Suzukian]

Maybe you missed my post, you can drill through a spark plug and make your own adapter for a pressure gauge. Not difficult to do, easier if you have a lathe, but I've done it by hand.

 

[Rich82GS750TZ]

I didn’t miss it. Thank you for the tip.

 

[Rob S.]

Towelie says:

"Don't forget to bring a towel!" :nevreness:

 

[93Bandit]

Thanks, Bob. I’ll consider it. Harbor freight has a few that are reasonably priced. But how do I know if they have the right adapter to fit the threaded hole in my intake port?

I think there might be some confusion here. The compression tester shouldn't be connected to the vacuum port on the intake. It is threaded into the spark plug hole. I believe most compression testers come with a few adapters for most standard plug thread sizes, 14mm 12mm and maybe 10mm. My 850 uses 14mm, not sure what your 750 uses but just verify plug thread diameter and check compression gauge specs. The Bosch tool I recommended covers most common sizes, and has extensions for plug holes that are recessed in the head like on our bikes.

Sounds like you have something else going on though, since new plugs didn't help. I agree with others, ensure adequate voltage at the coils and check the carb for # 4.

 

[Rich82GS750TZ]

93Bandit,
I'm sure you're right. Forgive me. I was thinking of the ports on the intake bosses on the back of the head that are used for carb tuning. My mistake. I've never done this before. Thanks for clarifying.

 

[93Bandit]

93Bandit,
I'm sure you're right. Forgive me. I was thinking of the ports on the intake bosses on the back of the head that are used for carb tuning. My mistake. I've never done this before. Thanks for clarifying.

No worries, glad I could help clarify! Not to worry about never this before, compression test is easy to do. There are tons of threads discussing the do's and don'ts of a compression test. Everyone starts somewhere. I'm fairly experienced with engines but there are plenty of things I've never done before. Learning every day.

 

[Rich82GS750TZ]

Not a lot done tonight. Have a meeting in a bit so could only start to take things apart. Got 3 of the 4 screw off number 4 carb lid. Stripped the last one. Yes, I Know, JIS, impact driver. Still stripped. I’ll cut a slot with the dremel and get it out. Have to quit for tonight though.

I’ve ordered a compression tester but will probably not get to testing till next week, Sunday evening at the earliest. I’ll be away all weekend. I did the only thing I could do: put my finger over each plug hole and run the starter, yes, throttle wide open. 1-3 audibly “chuffed” and felt strong, felt like it wanted to suck my finger into the hole. 4 was weak by comparison. Hardly empirical evidence, but I’ll have to wait on the gauge to have any numbers.

I’ve also ordered a cheap endoscopic camera for my phone. Always wanted one anyhow.

Measured 12v+ at the O/W + lead on both coils. I have no clue how to read ohms or what I’m doing here. Searched a bit but no luck. I have a multimeter. Would someone mind a brief instruction on how to set my meter, where to put the red and black leads. Sorry, not my forte. Would be greatly appreciated.

 

[Rich82GS750TZ]

OK, watched a video on measuring resistance. I got 3.7 ohms on the primary side of both coils. Can’t get a reading on the secondary sides. I’m sure I’m doing setting something wrong.

edit:
Figured it out.