Suzuki GS750. using oil.

[bob808]

• Members
• • 95

Hello again. You guys have helped me a lot in the past and I did think I was around finished with the engine, on this bike,but.

Suzuki GS750 24,000. miles, original pistons.

I'm using oil, using around 30ml over 50 miles. Blue smoke on start up.

History.

Head skimmed last year, it was warped. ground in valves. new springs

Finally got her set up, and running well.

Replaced seals on ; clutch push rod

gear change sender unit

cam chain tensioner.

No more leaks.

I did think about a leak down test but I will be taking the head off so is there any point?

When the head was skimmed, the barrels looked great, A1. ( mistake no. 1 ) I didnt change the rings.

I did change the valve stem seals.



How do I proceed?

I will put new valve stem seals on again. Belt and braces. ( this time).

Q.1. Is it worth changing the rings only?

Q.2. Should I, change the pistons, and rings, and re-hone the barrels?

Finally ( for the moment ?), Will you recommend manufactures of pistons and rings please?

 

[Rijko]

I would do a compression and leakdown test, would be a shame to do all the work and discover the valves leak and could have easily been re-lapped while you were working on it.

New pistons/rings are expensive, but the story might not end there : you may need new wrist pins (Wiseco for instance).
Unless you go for Cruzinimage (several have good experience with these cheap pistons), a new set pistons will set you back 500-700, boring cylinders another 100-150, it adds up quickly.

Mileage is fairly low, could very well be cylinder bore, rings and pistons are still ok.
Measure cylinder diameter, ring gaps and piston diameter as in the service manual or have it done.
Suzuki describes wear limits and does not recommend replacement unless worn in the manual.

Blue smoke on startup often is valve stem seals.
You may want to check / replace those before taking the engine apart.
I damaged 1 valve stem seal once when installing, the rubber lip on the inside of the seal was damaged.
That was all it took to start smoking on cold start ..

If this does not resolve it and have to take the top apart, don't forget to check the oil rings orientation : they could be mounted upside down.

 

[bwringer]

Yeah, I'd pull and ponder the plugs, and have a peek at the bores with an inexpensive bore camera... this could be as simple as one or more failed valve stem seals, which would be seen as oily carbon buildup.

These can be replaced easily enough without disassembly using the old rope trick or an air hold.

Some brands of aftermarket valve stem seals, such as in the Vesrah and Athena kits, are known to be completely lousy quality. OEM Suzuki, of course, is a good move, There are excellent quality aftermarket brands of Viton seals available as well.

One last bit of advice is that I've seen far too many GS engines and rings wrongly condemned based on faulty compression testing. If you do feel the need to do a compression test, pull the carbs or you'll never get usable results. Lots of bad Chinese gauges out there, too, and getting a good seal on the tester's hose is difficult. If you're getting bad results, suspect your testing or tester's sanity before you start taking the engine apart. If the bike runs strongly and starts quickly, you have good compression.

I'll agree that blue smoke on startup doesn't really sound like rings.

 

[rphillips]

Am I figuring this right?? 30ml per 50mi. = 1qt. per 1600 mi. More than you want to lose, but not terribly drastic. How many mi. since you had it apart, may get better as everything gets seated in. My new "80" GS1000 was using about that much after appx. 3000 mi. break in. My dealer didn't want to do anything about it and said put 20W/50 oil in it. It made a big difference, would get through oil change and be about 1 qt. low.... Just say'in

 

[bob808]

Am I figuring this right?? 30ml per 50mi. = 1qt. per 1600 mi. More than you want to lose, but not terribly drastic. How many mi. since you had it apart, may get better as everything gets seated in. My new "80" GS1000 was using about that much after appx. 3000 mi. break in. My dealer didn't want to do anything about it and said put 20W/50 oil in it. It made a big difference, would get through oil change and be about 1 qt. low.... Just say'in

350miles, I am using 20W/50 atm. Thank you

 

[bob808]

Yeah, I'd pull and ponder the plugs, and have a peek at the bores with an inexpensive bore camera... this could be as simple as one or more failed valve stem seals, which would be seen as oily carbon buildup.

These can be replaced easily enough without disassembly using the old rope trick or an air hold.

Some brands of aftermarket valve stem seals, such as in the Vesrah and Athena kits, are known to be completely lousy quality. OEM Suzuki, of course, is a good move, There are excellent quality aftermarket brands of Viton seals available as well.

One last bit of advice is that I've seen far too many GS engines and rings wrongly condemned based on faulty compression testing. If you do feel the need to do a compression test, pull the carbs or you'll never get usable results. Lots of bad Chinese gauges out there, too, and getting a good seal on the tester's hose is difficult. If you're getting bad results, suspect your testing or tester's sanity before you start taking the engine apart. If the bike runs strongly and starts quickly, you have good compression.

I'll agree that blue smoke on startup doesn't really sound like rings.

Can you name some brand that are good for Viton seals. Thank you.

 

[bob808]

I would do a compression and leakdown test, would be a shame to do all the work and discover the valves leak and could have easily been re-lapped while you were working on it.

New pistons/rings are expensive, but the story might not end there : you may need new wrist pins (Wiseco for instance).
Unless you go for Cruzinimage (several have good experience with these cheap pistons), a new set pistons will set you back 500-700, boring cylinders another 100-150, it adds up quickly.

Mileage is fairly low, could very well be cylinder bore, rings and pistons are still ok.
Measure cylinder diameter, ring gaps and piston diameter as in the service manual or have it done.
Suzuki describes wear limits and does not recommend replacement unless worn in the manual.

Blue smoke on startup often is valve stem seals.
You may want to check / replace those before taking the engine apart.
I damaged 1 valve stem seal once when installing, the rubber lip on the inside of the seal was damaged.
That was all it took to start smoking on cold start ..

If this does not resolve it and have to take the top apart, don't forget to check the oil rings orientation : they could be mounted upside down.

What am I checking, with the wrist pins, play?

 

[rphillips]

30ml = 1.01 oz... 1.01oz. (30ml) per 50 mi... 1 qt. = 32 oz... 32 oz X 50 mi. = 1600 mi pr. qt... Have the metric #'s have got me confused ?

 

[Cipher]

Why in God's name 20w50 is too viscous if mineral unless you're in Cairo at high noon towing a tent trailer.

 

[Rijko]

What am I checking, with the wrist pins, play?

The service manual describes wrist pin OD, piston hole ID, and wrist pin to bore limits.
I stopped measuring those because for the GS, they were almost always within tolerance.
I look at the small end eye if no visible damage and look at the wrist pin that should show some
very light running wear and call it good usually. Light wear looks more like a discoloration,
a dulled chrome, no noticeable rims or scars.
In your case, low mileage, i expect them to be real good.

The GT750 is a different matter, the protective layer inside the small end is often worn away.

Now i don't recall wether GS1000 or GT750 but years ago i tried mounting the Wiseco pistons using OEM wrist pins.
I mounted 1 circlip and pushed the wrist pin against it, was able to see the circlip groove, but the circlip
would not click into place.
Turns out the circlip-to-circlip distance was ever so slightly shorter than OEM so i had to order the
Wiseco wrist pins.
That's what i meant to say but i was not clear enough.. if you go for non-OEM pistons check if you need their
wrist pins too. Needless to say always use new circlips.
I have reused circlips as a young boy, and never had a problem.
But for the price better not take the risk.
Don't forget to mount the circlips with the opening pointing upward.

 

[bob808]

Why in God's name 20w50 is too viscous if mineral unless you're in Cairo at high noon towing a tent trailer.

What would you recommend?

 

[bob808]

The service manual describes wrist pin OD, piston hole ID, and wrist pin to bore limits.
I stopped measuring those because for the GS, they were almost always within tolerance.
I look at the small end eye if no visible damage and look at the wrist pin that should show some
very light running wear and call it good usually. Light wear looks more like a discoloration,
a dulled chrome, no noticeable rims or scars.
In your case, low mileage, i expect them to be real good.

The GT750 is a different matter, the protective layer inside the small end is often worn away.

Now i don't recall wether GS1000 or GT750 but years ago i tried mounting the Wiseco pistons using OEM wrist pins.
I mounted 1 circlip and pushed the wrist pin against it, was able to see the circlip groove, but the circlip
would not click into place.
Turns out the circlip-to-circlip distance was ever so slightly shorter than OEM so i had to order the
Wiseco wrist pins.
That's what i meant to say but i was not clear enough.. if you go for non-OEM pistons check if you need their
wrist pins too. Needless to say always use new circlips.
I have reused circlips as a young boy, and never had a problem.
But for the price better not take the risk.
Don't forget to mount the circlips with the opening pointing upward.

Thank you.
I will remember this.

 

[Brendan W]

Second for Brian's comments on stem seals.
Where did you get the replacements from?
I got some with a complete kit from NE and I just knew they were junk by the feel of how they went on so went and got better ones.
Not OEM but when it was done I had no start up smoke and practically zero oil consumption on a 50000 mile motor.
I had been losing 1000ml every 200 miles from a combination of a bad headgasket leak at the front between 2&3 and stem seal leak.
Stem leaks are visible at the exhaust ports with the headers off.

 

[rphillips]

1000ml = appx. 1 qt pr 200 mi... That's a whole lot.

 

[bob808]

Ok so head off. Ring gap when squeezed is around 3 mm?? Will order bore measuring tool today.Next stop is machine shop. Problem is nearest one is 80 miles away. Keep you posted.

 

[Brendan W]

1000ml = appx. 1 qt pr 200 mi... That's a whole lot.

And some.....
You know it's time to fix leaks when you plant your boot at a stop and it slips

 

[bob808]

I did not do the leak down ( not intentionally), I just started taking it apart. I already know all the valve specs are within tolerance and will rebed the valves and reseal the stems on rebuilding.

The pistons have not been cleaned they are coated lightly with oil. HUH !
I guessed the gaps looked big ( on the pistons) . But will gap check when required
The bores are great and pistons clean.

I will now take it to the engineer to have the bores measured, its ?30.00 for a tool and I dont think the shop would charge much more. Then they can hone or rebore as required, and I know its good.
Worried about them not being round. Thanks.

 

[Cipher]

What would you recommend?

Castor oil jk. I saw Aberdeen and assumed lowish ambient temperature being combined with short run times to be not allowing oil to flow adequately.

But seriously during your rebuild did you check the play in the valve to guide? Excessive slop would be hard on seals.

As a superfluous aside too light a synthetic runs through my old bike at a disturbing rate. Rotella t6 burns off but t5 mineral does not drop significantly between oil changes.
this is whilst being flogged in a 30 deg. plus environment.

 

[bob808]

Castor oil jk. I saw Aberdeen and assumed lowish ambient temperature being combined with short run times to be not allowing oil to flow adequately.

But seriously during your rebuild did you check the play in the valve to guide? Excessive slop would be hard on seals.

As a superfluous aside too light a synthetic runs through my old bike at a disturbing rate. Rotella t6 burns off but t5 mineral does not drop significantly between oil changes.
this is whilst being flogged in a 30 deg. plus environment.

Yeah checked all the valve specs, even bought a set of ball gauges. I found my piston ring gaps seem very large. How do I upload pics?

 

[bob808]

So just a quick update, Went to the machine shop. The barrels are oval front to back, and enlarged bottom to top. The pistons are toast too. So its a re-bore then. Just going to stick to 750cc cos the head has been skimmed previously. Thanks for the advice. Any opinions on IMD Pistons?