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compression diminishes to nothing from 1 to 4

  • Thread starter Thread starter Paul's Zuki
  • Start date Start date
P

Paul's Zuki

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So, I just rebuilt my engine clean all the carbon deposits of the valves and such and have put everything back together. I checked that the carbs were getting fuel - check; checked that I had a spark - check; went to check compression and ah ha. very low to no compression. So I did the wet test, poured the teaspoon of oil and recheck. 1st one read about 95, 2nd about 30, 3rd -0, & 4th about 30. I'm stumped. I'm not sure if I should just pull the valves and replace them or if there is another option. that is probably the last thing that is keeping me from firing her up. any ideas?
 
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First, add your bike to your sig so we know what we're talking about here.

Wow, 0 on #3 and you just opened the motor? I guess you would have noticed if you had cracked valves or a holed piston. Those results were consistent over two runs? Holding the throttle wide open? I mean cold compression #'s don't mean all that much but you should do better than zero! Battery is fully charged? Re-check valve clearances and while you're in there verify timing and valve operation. Yet you're getting 95 psi on #1? Is yours a roller bearing crank motor? Could your crank be twisted? Are #1/#4 at TDC at the same time and #2/#3 at BDC (and vice-versa).
 
Well, the bike isn't finished quite yet, that's the only reason no photo. But, yeah, it seemed really odd to me. the 3rd piston did have a hole in it, but I replaced that and I put new piston rings on every one of them. the valves seemed to seat pretty well. TDC is perfect, timing is perfect. crank is not twisted. I completly tore the engine case apart and rebuilt everything minus replacing the valves, but I didn't think it needed and (maybe?) it might the culprit? Even after doing the wet test on chamber 1 it went up an additional 15 psi, but the others are just really throwing me off. maybe a bad compression tester, but if that was the case and the compression was good she should be starting up. Agghhhhh, anyways I have 2 months to figure it out and hopefully it will be sooner than that, but i have a ratbob show i want to enter it in and you have to ride it in to even qualify.
 
How did the valves look when you took them out to clean the head?
 
they looked fine. they had your normal carbon deposit for a bike with 9000 miles on it. That's what's really weird to me. all the springs felt solid and seemed to seat real well.
 
I assume you adjusted the valves so won't go there.

How about some photos showing how you timed the cams? You need 1-4 T aligned on the crank, 1-- mark on exhaust cam pointing at gasket surface, and the specified number of chain pins between 2 and 3.
 
Nessism said:
I assume you adjusted the valves so won't go there.

How about some photos showing how you timed the cams? You need 1-4 T aligned on the crank, 1-- mark on exhaust cam pointing at gasket surface, and the specified number of chain pins between 2 and 3.
Click to expand...

I did do the 1 & 4 and counted the number of pins between 2 & 3, but let me ask you about the valve adjustment. in my book of the bike it's very vague if any info on actually adjusting. is that something i can find on the resource website?
 
You pulled the head but didn't adjust the valves?
 
guilty as charged. Looking back at the process. I just followed the book on dissassembly and reassembly to replace gaskets and sort throughout the motor, but failed to do a valve adjustment. Do you think that not adjusting the valves would really cause no compression? I am asking cause I don't know. If so then I guess I need to pull valve cover and check the measurements.
 
Paul's Zuki said:
Do you think that not adjusting the valves would really cause no compression?
Click to expand...

Yes, the valves cannot close if there is no clearance. If the valves don't close, there is no compression. The valves also tend to burn up from running too tight, if the bike runs enough to get hot.
 
Yeah, you have to check and adjust valve clearances any time you remove the camshafts or bearing caps.
 
Ok. looks like I'll be checking those valves in the next couple of days. Now to the million dollar question were can I get the shims of different sizes?
 
nevermind found them on bikebandit.com. anyone know the od size though? 1978 GS550E
 
Paul's Zuki said:
Ok. looks like I'll be checking those valves in the next couple of days. Now to the million dollar question were can I get the shims of different sizes?
Click to expand...

Did you track the buckets and shims and put them back to the valves where they came from?

If you don't have anyone locally you can get them from (check your dealer if you have one they may have some in stock), Z1 Enterprises sells them for about $5 each plus shipping; they also sell the shim tool for about $15 IIRC. Another source is the Shim Club here run by member ghostgs1; as a member (which requires shim or monetary donation) you can exchange shims. Forum searches will get you there. Make sure you get Suzuki 29.5mm shims, not Kawasaki 29mm ones. Having a very thin measuring shim gives you something to swap in and measure when there's no clearance at all.

If your valves are hanging open you'll probably need to go down two sizes to get them in range. If you can't measure the gap with a .03mm feeler or 0.0015" then try turning the bucket by hand. If it doesn't turn easily then you have 0 or negative clearance. Have calipers or a micrometer handy as many times the printed size will have worn off.
 
mike_of_bbg said:
Did you track the buckets and shims and put them back to the valves where they came from?

If you don't have anyone locally you can get them from (check your dealer if you have one they may have some in stock), Z1 Enterprises sells them for about $5 each plus shipping; they also sell the shim tool for about $15 IIRC. Another source is the Shim Club here run by member ghostgs1; as a member (which requires shim or monetary donation) you can exchange shims. Forum searches will get you there. Make sure you get Suzuki 29.5mm shims, not Kawasaki 29mm ones. Having a very thin measuring shim gives you something to swap in and measure when there's no clearance at all.

If your valves are hanging open you'll probably need to go down two sizes to get them in range. If you can't measure the gap with a .03mm feeler or 0.0015" then try turning the bucket by hand. If it doesn't turn easily then you have 0 or negative clearance. Have calipers or a micrometer handy as many times the printed size will have worn off.
Click to expand...

Yes, I did track the buckets and shims to each valve. I will make note of that when checking. Oh, the beauty of working on our old beloved bikes.:p
 
You should have pulled the valves out of the head, cleaned everything, and replace the valve stem seals. Those seals lead a very rough life with the high heat and all, and leakage is very common.

Edit: just reread this thread and as I understand it you split the cases and everything but didn't service the head or even check the valve clearances? Geeze man, what where you thinking?
 
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Nessism said:
You should have pulled the valves out of the head, cleaned everything, and replace the valve stem seals. Those seals lead a very rough life with the high heat and all, and leakage is very common.
Click to expand...

Not to mention they are 33 years old and hard as a rock!
 
How do you remove the valve stem seals. My book only says that I should replace is there is movement left to right (i'm replacing them anyways b/c they are old azz hell), but it doesn't say how to remove them. It says if replacement needed, special tools are needed and should be taken to a suzuki service tech (of course). Will it really be that hard? any advice?
 
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