Going ahead with engine rebuild

[TheNewGuy]

I bought a 1977 gs750 two months ago. Bike has 18k original miles. Compression is 90 on all cylinders. Carbs have been dipped and o rings replaced from cycle o rings. Valves have been adjusted. Ever since I bought the bike the engine itself has smoked after warming up. Not the exhaust, the engine itself. Possible blown head gasket? Am I able to just do the head gasket and not have to replace the rings, valve seals, hone cylinders ect? All input is greatly appreciated

 

[Nessism]

How lucky do you feel?

 

[roeme]

I never been into an engine that far; but even to me it's obvious that it's a good idea to replace rings/base gasket when you're taking off the head. It really doesn't add much in terms of work, does it?

Not sure about work involved with the the valve stem seals, I'd presume not that much?

..but why half-ass it when you're diving into the engine anyway: You're taking off the head at the very least, so you have all the parts off that are most likely responsible for the smoke, shouldn't be too much work to measure/service them according to the manual?

But some more knowledgeable guys may want to chime in.

 

[Guest]

Download a service manual for your bike, if you haven't already (http://members.dslextreme.com/users/bikecliff/). When you take the engine apart, you can measure the rings and the cylinders per the factory manual and see if they are in spec (this will require investing in some special tools). I would at least replace the head and base gasket, along with valve seals. Make a call about the rings once you have it open. If they are stuck in the piston grooves a good soak in carb cleaner could bring them out so you can measure the gaps, and is a likely cause of the low compression.

 

[sharpy]

what you mean the engine smokes? was only one time or is there a leak somewhere. if engine hasnt been apart and it dont smoke ill look for the sorce of that smoke and just fix it for now.

 

[Steve]

OK, diagnosis time:

- Was your compression test done while the engine was HOT?
- Was the throttle held wide open during the test?
- Did you do another compression test after adding a bit of oil to each cylinder?
- Have you adjusted the valves?
- Does it smoke while accelerating?
- Does it smoke while DEccerating?
- Does it smoke more when cold or hot?

Now, let's interpret the questions:
- If the test was not done hot, it's only good for generalization, not for proper diagnosis.
- If the throttle was not held open, the test is meaningless, as the engine simply could not get enough air to compress into meaningful numbers.
- Adding a bit of oil will help determine if the low numbers are due to rings or valves.
- If the valves are tight, they might leak enough to affect compression numbers. If your bike starts easily when cold, the valves are likely not too tight.
- If it smokes more while accelerating, it's likely the rings.
- If it smokes more while deccelerating, it's likely the valve seals. Valve seals also tend to smoke when engine is cold and/or idling.

Now, just a few points on major engine work:
- In the process of removing the head, you will inevitably jiggle the cylinders. That will disturb the base gasket.
- To replace the base gasket, you will need to remove the cylinders.
- Some will hone the cylinders lightly any time they are available, others will say that there is no need if you are keeping the same rings.
- If you are replacing the rings, DEFINITELY have the cylinders honed, but check them for roundness first.
- If you replace the rings, pull the pistons to make it easier to clean the ring grooves. This will require new keepers for the wrist pins.
- If you feel really lucky and insist on only pulling the head, change the valve seals. They may be all that's leaking now, but you will disturb everything below them.

Good luck with your project. :encouragement:

.

 

[TheNewGuy]

OK, diagnosis time:

- Was your compression test done while the engine was HOT?
- Was the throttle held wide open during the test?
- Did you do another compression test after adding a bit of oil to each cylinder?
- Have you adjusted the valves?
- Does it smoke while accelerating?
- Does it smoke while DEccerating?
- Does it smoke more when cold or hot?

Now, let's interpret the questions:
- If the test was not done hot, it's only good for generalization, not for proper diagnosis.
- If the throttle was not held open, the test is meaningless, as the engine simply could not get enough air to compress into meaningful numbers.
- Adding a bit of oil will help determine if the low numbers are due to rings or valves.
- If the valves are tight, they might leak enough to affect compression numbers. If your bike starts easily when cold, the valves are likely not too tight.
- If it smokes more while accelerating, it's likely the rings.
- If it smokes more while deccelerating, it's likely the valve seals. Valve seals also tend to smoke when engine is cold and/or idling.

Now, just a few points on major engine work:
- In the process of removing the head, you will inevitably jiggle the cylinders. That will disturb the base gasket.
- To replace the base gasket, you will need to remove the cylinders.
- Some will hone the cylinders lightly any time they are available, others will say that there is no need if you are keeping the same rings.
- If you are replacing the rings, DEFINITELY have the cylinders honed, but check them for roundness first.
- If you replace the rings, pull the pistons to make it easier to clean the ring grooves. This will require new keepers for the wrist pins.
- If you feel really lucky and insist on only pulling the head, change the valve seals. They may be all that's leaking now, but you will disturb everything below them.

Good luck with your project. :encouragement:

.

Yes the test was done hot with the throttle open. Used two different gauges on two seperate tests. Same results each time. Did a wet compression test after and the compression jumped to 150-160 in all cylinders. I'm looking the the gaskets. Do I need to order the center rectangle o ring and the o rings for each cylinder?

 

[alke46]

The bike is 41 years old. The o rings you mention are the same age. Wouldn't it just make sense to replace that old rubber while the engine is apart?

 

[Steve]

Those gaskets should come with a full gasket set. You can get just an upper-end set or a full rebuild set, but make sure the head gasket and base gasket are OEM Suzuki gaskets. Yes, they cost about as much as a full gasket set from one of the other vendors, but you will not have to do the job twice. A full OEM gasket set should cost less than two aftermarket sets, but it's worth the price.

Also, for reference, some of the well-known aftermarket kits include Athena, Cometic and Vesrah. Most of us will advise that you do NOT get Athena.
Between Cometic and Vesrah, I think more prefer Vesrah, but can't say for sure.

.

 

[TheNewGuy]

I got the oem gaskets ordered. The only things Im concerned with doing this are removing the cam tensioner and getting the timing set correctly. Also, getting the cylinder over the new piston rings by myself. Anyone have any suggestions on this? Thank you

 

[chuck hahn]

I cut thin strips of 3/8 plywood just wide enough to fit between the bottom of the piston skirt and the cylinders studs. Then i wrap them in masking tape to prevent wood chips falling into crankcase. Next I rotate the crank till all 4 pistons set on said plywood shims..making them all even in height. Now I start the cylinders down on top of the pistons just to the top ring ( You should have already orientated the rings per the service manuals description ).

Next i take a small flat tip screwdriver on each side of a pistons rings and gently start each piston a little. Working back and forth from piston to piston while tapping the jugs down youll get all 4 into the barrels. Now the trick. Ever so slightly move the crank and slip out the two pistons shims that get loose. Then wiggle the crank a little to get the other two out. Once all 4 sets shims are out hold the crank still with a wrench on the 19MM nut and tap the cylinders home.

Youll notice a bevel to the inside of the barrels that is "supposed to" help feed the rings in but dont count on it being that simple...LOL

Then the rest is just follow the service manual step by step and youll be fine.

 

[jsandidge]

I cut thin strips of 3/8 plywood just wide enough to fit between the bottom of the piston skirt and the cylinders studs. Then i wrap them in masking tape to prevent wood chips falling into crankcase. Next I rotate the crank till all 4 pistons set on said plywood shims..making them all even in height. Now I start the cylinders down on top of the pistons just to the top ring ( You should have already orientated the rings per the service manuals description ).

Next i take a small flat tip screwdriver on each side of a pistons rings and gently start each piston a little. Working back and forth from piston to piston while tapping the jugs down youll get all 4 into the barrels. Now the trick. Ever so slightly move the crank and slip out the two pistons shims that get loose. Then wiggle the crank a little to get the other two out. Once all 4 shims are out hold the crank still with a wrench on the 19MM nut and tap the cylinders home.

Youll notice a bevel to the inside of the barrels that is "supposed to" help feed the rings in but dont count on it being that simple...LOL

Then the rest is just follow the service manual step by step and youll be fine.

You make it sound easy Chuck.

 

[chuck hahn]

I edited the post to say all 4 SETS of shims from under the pistons. And another note. Make the shim wide enough so they go kinda close to the connecting rod. This will give lots of surface for the piston to rest on and eliminate a lot of potential tilting of the pistons as you work them in to the barrels. Object is to stabalize the pistons upright solidly so the feed straight and smooth.

 

[chuck hahn]

It is actually really easy even without ring compressors...and a few resettings under your belt. They will seem to fall on after youve got it down a few times.

 

[chuck hahn]

Crap..another tidbit. Hold the cam chain up as you settle the pistons onto shims with the crank. This prevents it from rolling onto itself and jamming Which you dont want to find out AFTER the pistons are in. Ask me how I know...LOL

 

[hannibal]

I got the oem gaskets ordered. The only things Im concerned with doing this are removing the cam tensioner and getting the timing set correctly. Also, getting the cylinder over the new piston rings by myself. Anyone have any suggestions on this? Thank you

Did you find an OEM gasket set? I was lucky to find one on Ebay but couldn't find the advertised part number anywhere to verify. Bought it and it was mostly complete.

This was my first time opening an engine. As for reinstalling the cylinders, I recommend patience, your favorite adult beverage, and more time and patience.

Since the head is off, I lapped valves and replaced valve stems. Since the cylinders are off, I replaced the rings and honed the cylinders.

Don't sweat the cam tensioner removal. That's straight forward in the service manual. Reassembly and setting timing is well explained in the manual as well.

 

[TheNewGuy]

Thank you all for the in depth knowledge. Will keep everyone posted. Thanks again

 

[Guest]

The bike is 41 years old. The o rings you mention are the same age. Wouldn't it just make sense to replace that old rubber while the engine is apart?

Just do a full rebuild while you have the engine apart anyway, so you don't have to take it apart again later.

 

[TheNewGuy]

Got the head off. The jugs are Stuck though. Any ideas other than the rubber mallet ive been trying

 

[alke46]

Got the head off. The jugs are Stuck though. Any ideas other than the rubber mallet ive been trying

On mine, I was able to get one corner to pry up just a bit then I put a wooden shim into the opening. Went to the opposite side and did the same thing. Once both sides had a tapered shim under it, I just lightly tapped the thicker end of the shim to drive it under the jugs. Once the seal is broken you can then lift it off the crankcase.
Good luck.