GS750 8-valve smoking/oil consumption

[The1970's]

I continue my search for the perfect GS750 by tackling one issue at a time. This month's issue to look into is the engine. Since buying the bike in May I've put about 4,000 miles on it. The total now is just over 30,000. Since I have owned it it seems I've been going through about half a quart (or whatever it takes from low to full markes) of oil every 300-600 miles. I don't really notice any smoking when I'm riding it but friends riding behind me have noted a blue smoke only at high throttle settings. It does have a small leak at the oil pan gasket and a slight weep from the valve cover, but neither of these even produce a noticeable drip when parked or idling so I don't think its leaking that oil out. I have ordered a oil pan gasket though so at some point I will pull the pan off and replace it.

Compressions all read between 90-120 with #3/#4 being higher and #1/#2 being lower. Dripping some oil in the cylinders does increase the numbers by about 5 PSI or so. I had a hard time getting the cheap compression tester to seal on the head so I am not completely confident in the readings.

I had always been ready to do a top end rebuild in the somewhat near future, but the bike runs great and is plenty powerful so I've just been riding it. Is there anything else to check or is the solution to pull it apart and inspect? If I put the oil pan gasket in is there anything I can check while the pan is off that may elude to the problem?

[alke46]

Sounds exactly like mine. You don't mention the age of the bike but my first inclination would be dried out, hardened valve stem seals. Mine is getting ready for a top end inspection and I already have the seals ready to go in and I am also going to check the rings to make sure they are still within tolerance.


Good luck and keep us updated with your progress.

[The1970's]

Sounds exactly like mine. You don't mention the age of the bike but my first inclination would be dried out, hardened valve stem seals. Mine is getting ready for a top end inspection and I already have the seals ready to go in and I am also going to check the rings to make sure they are still within tolerance.


Good luck and keep us updated with your progress.

I had thought of that and was thinking about throwing some new ones in because they are relatively cheap. I read in one of the threads on here of someone replacing them without removing the head. Any experience? Mine is a 1978 and judging by some of the work I've done to it, it has sat for some period of time under someone else's ownership.

[alke46]

No experience with doing the job without head removal. I have heard a bit about it with using rope or else air to hold the valve up while removing the springs and collets. I think mine will be getting new gaskets at the base, head, camshaft cover and the cam chain tensioner.
My #3 cylinder is slightly lower on compression than the other 3 so I want to see if there is a reason for that.

[Big T]

I know AZR did the valve seal replacement without removing the head. He might have done a write up on it


Nothing in the oil pan would cause oil usage. Clean the pick up screen while you're in there

[chuck hahn]

If its gonna get torn into, If it were mine, the rings AND valve stems would be done. With the jugs removed you can clean up the piston tops of carbon too. Head off you can clean the domes and clean the valves when you remove them. Lapp the valves and be done for the next 20 years or so.

[Carter Turk]

I had thought of that and was thinking about throwing some new ones in because they are relatively cheap. I read in one of the threads on here of someone replacing them without removing the head. Any experience? Mine is a 1978 and judging by some of the work I've done to it, it has sat for some period of time under someone else's ownership.

Not to encourage you to do it with the head on.

I had success with thin rope inserted through spark plug holes and the pistons raised by turning the crank on the ignition side.
My engine was out of the frame, if I remember correctly, to put a new transmission in without disturbing the pistons, cams and crank.

While it was out, I decided to renew valve stem seals.
Used a deep socket with 2 windows cut in the side to access the valve spring retainers.
I left the bottom portion of the socket intact below the windows, to make it easier to push evenly on the valve spring.
Tried to make a hokey levered removal arm that failed miserably.
Ended up just using my hand to push down on the spring and it worked.
Might be rather difficult, but not impossible to get to the inner cylinder valves, while still in the frame. No experience doing it that way.

Prior to this I had never touched anything valve related except for valve adjustments- the easy non shim kind, with locknut, but 8 more to adjust.

[Steve]

I read in one of the threads on here of someone replacing them without removing the head. Any experience?

Carter Turk is speaking from experience. I have done it on a car, but not a GS, the car is easier because you don't have shims and buckets recessed into the head.

As he mentioned, you will have to come up with some means of compressing the springs and removing the keepers. Actually, it's not all that hard to remove them, the HARD part is getting them back together. Doing it this way will be the only "cheap" way. If you decide to pull the head to do it the "normal" way, you should really pull the cylinders and change the base gasket, because its seal will be broken when you jiggle the cylinders while removing the head. This will add a few bucks for gaskets.

If you decide that you need to (want to?) replace the rings, be prepared for sticker shock. A set of rings will likely run about $150, and the gaskets to put it all back together will be in the $200 range. Most of us HIGHLY recommend using Suzuki gaskets, especially for the cylinder base and head. I have compared prices for my 850, and found that Suzuki base and head gaskets, along with an aftermarket 'complete' gasket set (make sure it's NOT Athena) is about $200. At the time, a full Suzuki set was about $210, which pretty much offset the extra shipping charges of ordering parts from two shippers. Your prices will likely be different, but the comparison should be close.


.

[chuck hahn]

I have used 3 or 4 sets from Cruzinimages without problems. So rings are under 50 bucks actually.

https://www.ebay.com/itm/77-79-SUZUKI-GS750-STANDARD-PISTON-RINGS-SET-4-PISTON-RINGS-11-GS750PR/141984349328?hash=item210eed3c90:g:dBEAAOSw2XFUY0LQ&vxp=mtr

[hannibal]

If you decide that you need to (want to?) replace the rings, be prepared for sticker shock. A set of rings will likely run about $150, and the gaskets to put it all back together will be in the $200 range. Most of us HIGHLY recommend using Suzuki gaskets, especially for the cylinder base and head. I have compared prices for my 850, and found that Suzuki base and head gaskets, along with an aftermarket 'complete' gasket set (make sure it's NOT Athena) is about $200. At the time, a full Suzuki set was about $210, which pretty much offset the extra shipping charges of ordering parts from two shippers. Your prices will likely be different, but the comparison should be close.

I opened my motor this spring. Steve's prices are spot on. I paid about $140 plus shipping for rings but got lucky and found an OEM gasket set for about $100 on Ebay. Thought I bought OEM valve seals but they turned out to be Versah brand. The set of 8 was $30.

I had the motor removed from the bike so taking the head off and replacing gaskets and rings and honing the cylinders was a no brainer.

[The1970's]

I know that the right thing to do here would probably pull the head and have a look at the bores and rings but here's where I'm at: I really like the bike and plan to keep it for a long time and rack up some serious mileage. So if I'm going to do the top end I figure I may as well split the cases, put in an oil pump, bearings, pistons, new valves and guides. Do it right and not have to worry about it for 60,000 miles or so. At this point, it makes sense to me to throw a set of valve seals in it and see where i'm at. Maybe give it another 10,000 miles of life before it needs the full overhaul. I guess my question here is what are the chances of fixing it or at least making it better with just valve seals? I think I can figure a way of changing them in the bike with the head on but if there's only a minor chance of fixing it I probably wont bother with it.

[chuck hahn]

Valve seals wont hurt a thing. BUT what if its a combo of valve stem seals AND rings?? Then what. as for splitting the cases and adding an oil pump..totally 100% unnecessary. That 750 has the high volume gearing and unless you run that thing out of oil dry as a bone it will run 100,000 miles without a hiccup. If you just do the rings and refresh everything in the head ( not including valve guides) youll be fine for 20 more years.

May i ask if this is your first GS bike??? If so, i see your worrying. But youve got nothing to worry about in that lower end..keep regular oil changes and rest easy about it.

[The1970's]

May i ask if this is your first GS bike??? If so, i see your worrying. But youve got nothing to worry about in that lower end..keep regular oil changes and rest easy about it.

First GS yes, I do have a 72 CB500 as well (I really need to update my signature) and before that had a CB400. I may be worrying a little too much, but I used to work at a machine shop assembling engines which where mostly older cars so the idea of having everything new to me sounds great.

Also while i'm at it, what do most people change the oil at? I've been doing somewhere between 1500-2000 intervals. when it gets up near 2000 I notice a little more oil consumption and I change it

[Nessism]

If you got the gumption, do the seals. Viton seals are one of the few aftermarket parts that are better than OEM Suzuki parts. Nothing to lose but a little time and effort.

[The1970's]

If you got the gumption, do the seals. Viton seals are one of the few aftermarket parts that are better than OEM Suzuki parts. Nothing to lose but a little time and effort.

I'm going to give it a go, I'll give an update with the results as well as the method I find worked best.