1979 GS750 Top end

[adamchatum]

Hey guys, did a compression test on my bike and had only ten psi on my #3. Took the head off and found a cracked exhaust valve.
Would it be a good idea to replace only one valve or do all four? I'd rather do one for the cost.
Also, can you put a 16 valve head on this engine/cylinder, to replace the 8 valve? Probably need different pistons huh? Just asking because the wrecker has one down the road.
Thanks

[7981GS]

16 valve heads don't fit on 8 valve engines.
Replace the bad valve, clean up all 8 valve seats, the other 7 valves and replace all of the valve stem oil seals.
While you are at it, you could spend a few minutes and introduce yourself to the forum in the new member section and your questions will get answered much more rapidly.
I don't know exactly why that is so but, I see it all of the time here.

Daniel

[BassCliff]

Greetings and Salutations!!

Hi Mr. adamchatum,

Are any other valves burned? These engines are pretty bullet proof providing they get a modicum of maintenance. After a careful inspection to be certain, you can just replace what's busted and get all of the other maintenance up to date. Or you could go overboard and, while the engine is down that far, replace the base and head gaskets, rings, hone the cylinders, replace valve seals, etc. But all of that is probably not necessary.

Anyway, let me dump a TON if information on you, and share some GS lovin'.

I just stopped by to welcome you to the forum in my own, special way.

If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", "Top 15 Tips For GS Happiness", the Carb Cleanup Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. Now let me roll out the welcome mat for you...



Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

[Nessism]

Hey guys, did a compression test on my bike and had only ten psi on my #3. Took the head off and found a cracked exhaust valve.
Would it be a good idea to replace only one valve or do all four? I'd rather do one for the cost.
Also, can you put a 16 valve head on this engine/cylinder, to replace the 8 valve? Probably need different pistons huh? Just asking because the wrecker has one down the road.
Thanks

A cracked valve is most often the result of neglected valve adjustment. I'd remove all the valves and inspect everything carefully before deciding on what needs to be replaced.

[adamchatum]

Thanks for the welcome everyone.
I just got this bike for fathers day from my wife. She found it for $150. Couldn't ask for a better wife huh? Its a bit of a project, but I'm more than game.
I'm going to order a new valve. But in the mean time I'll disassemble the rest of the head and do a good clean and valve lapping. Hoping to rise the compression a little.
Shims were good. All buckets were turning, and gaps were below .0015".
Bike only has 33,000 k's.
I'm going to try and post a pic of the cracked valve.

[adamchatum]

Here is the valve.

[Nessism]

Shims were good. All buckets were turning, and gaps were below .0015".
.

Nothing "good" about those shims. They are too thin.

And yes, good wife you got there. Does she have a sister?

[adamchatum]

The manual says 0.0012 - 0.0031. Is that a bit too small a gap?
Yeah, she has a sister. But you'll have to pry her from New Zealand.
Thanks

[Nessism]

The manual says 0.0012 - 0.0031. Is that a bit too small a gap?

and gaps were below .0015"

What was your question again?

[hjfisk]

The manual says 0.0012 - 0.0031. Is that a bit too small a gap?
Yeah, she has a sister. But you'll have to pry her from New Zealand.
Thanks

I don't know if you realize it or not but you valves will tighten with time not loosen up like a motor with adjustable stems, shim motors tighten so you want to be on the loser side not tighter. That is why your valve cracked in the first place more than likely

[BassCliff]

Hi,

I'm a simple man. It's a metric bike so I use metric measurements for most stuff. The valve clearance spec is 0.03mm to 0.08mm. It doesn't hurt to run a little looser than that, especially on the exhaust valves. Some of my clearances are 0.10mm. It's a little noisier than if the clearances were tight, but the engine breathes better and the valves last longer.

0.03mm = 0.00118 inches
0.08mm = 0.00135 inches
0.10mm = 0.00394 inches

Feel free to peruse my little website. I think you'll find some useful stuff there.


Thank you for your indulgence,

BassCliff

[Nessism]

Hi,

I'm a simple man. It's a metric bike so I use metric measurements for most stuff. The valve clearance spec is 0.03mm to 0.08mm. It doesn't hurt to run a little looser than that, especially on the exhaust valves. Some of my clearances are 0.10mm. It's a little noisier than if the clearances were tight, but the engine breathes better and the valves last longer.

0.03mm = 0.00118 inches
0.08mm = 0.00135 inches - make that .00315
0.10mm = 0.00394 inches

Feel free to peruse my little website. I think you'll find some useful stuff there.


Thank you for your indulgence,

BassCliff

Fixed it for you cliff!

[BassCliff]

Fixed it for you cliff!

Oops, thanks Ed.

I think that's why I use the metrics.


One of these days I'll learn to type.


Cliff