How can a crank get like this?

[Guest]

This bike is my new rescue project. It's a 1982 GS550L 8-valve that I picked up on Saturday.

PO says he had it running, but poorly, as recently as September. He took it to a mechanic, who told him the CDI box is bad (causing the bike to die after several minutes) and the carbs need to be rebuilt. When he bought it the clutch was going but it's apparently completely gone now. There was oil seeping from the left side of the head gasket, but the mechanic said that wasn't affecting the cylinders. Too much $$$ for him, and he's not capable of the work so he gave up on it. PO let it sit for the winter too with no gas in the tank (yet didn't drain the float bowls) so there's no doubt now it needs a carb cleaning and now it has some rust in the tank.

OK, I get the bike home. I wouldn't even try to start it without cleaning the carbs and the tank first. So my first order of business is to run a compression test. She turns over smoothly with a good batt. 75 psi cold/dry on cylinder #1. Ugh. #2 is even worse: 65 PSI. Life gets better on the right-hand side: 115 on #3 and 125 on #4. Yeah, but 65 is WAY low. Pressures get about 10-15 psi better wet in all cylinders, so the rings aren't that bad. I also notice at this point that the plugs are one heat range hotter than spec. So I'm fully expecting a couple of cooked valves now.

(it's really hard for me to believe that he could have taken it to a mechanic with compression that low in two cylinders and a suspect head gasket and said mechanic say it only needs a carb rebuild...)

Oh yeah, and the outer rings on the plugs from #1 and #2 were almost totally clean.

Drained the crankcase, which apparently held about a 50/50 oil/gas mixture. Ugh. Off come the tank, carbs, and valve cover. I check valve clearances. Six of eight are OK, two are too tight for my .0015" feeler. One is on #2 with the lowest comp, but #1's check out. The other unmeasurable gap was on #3, which was in the OK compression range. I have yet to find a local source for .01 mm feelers. Man that's a tight tolerance! The timing marks on the cam shafts and ignition check out.

OK, off with the head! Exhaust splits on it's way off the bike. Ugh. There's no major valve damage that I or my friend can see. No holes in pistons. No major cracks in the head or scorch marks on the gasket. But maybe it was a bad head gasket after all? Cylinder walls 2 and 3 feel good: no major scoring or scratches. Turn the crank and check 1 & 4 at BDC - no scoring.

My friend is turning the crank, looking for signs of binding; nothing. He stops between centers, then I notice that #2 and #3 are about 3/8" apart in travel. Correct me if I'm wrong, but that seems very wrong. Measure #1 and #4, similar story. Further investigation reveals that #1 and #2 are hitting TDC (and yes, they're reaching TDC) maybe 10-15 degrees advanced from the cam and points timing. #1 reaches TDC when the mark is above the letter F - not the line it marks - on the timing guide.

Now I'm feeling awfully sick. I hadn't done much looking about the bottoms on these motors. Now I have more questions than answers.

• Today I got the crankcase off and have it up on the bench. Any advice/tips/gotchas for the disassembly?
• Does the crank come as pieces or unitized? Could somebody have re-assembled it incorrectly to cause this? The drawings in the parts fiche show an assembly of dozens of parts with the roller bearings. The Suz service manual just shows checking and "replace if bad".
• Should I just try to find a used crank somewhere? Can they be swapped between blocks? (some searching through the old Q&A suggests yes to the latter)
• It seems kind of obvious to say yes, but would this timing cause the low compression #'s in those two cylinders? I mean, even with the timing off they still have to pass TDC with the valves closed toward the end of the compression cycle - albeit with a shortened intake cycle!

I'll attach a pic. It's hard to see that #4 and #1 are off (#4 is lower), but it's pretty clear that #2 and #3 are off.

[waterman]

From your description it sounds like a royally twisted crank. It could be replaced but 550's are plentiful and cheap, should be able to find a decent replacement motor for little money. I purchased a running 82550L for less than $400 two years ago.

[cbxchris]

Yeap its twisted.

Two options which are as already mentioned find a donor bike or send it off to be reindexed and welded. You also might have a rod bearing out causing part of the problem. Roller bearing engines are EASY to work on. Just pay attention to bearing with pins,etc. that have line up holes in the cases when reassembling. Good time to check the tranny out while out,replace the timing chain and just a good once over.

[seekinsoul]

Sounds like your crank is twisted. I had the same problem when I got my '82 550L, good compression on #3 & #4, low on #1 & #2, etc. These cranks are made from pieces that are pressed together, and feature roller bearings instead of being one piece cranks with plain bearings. It's likely that the crank "twisted" in the center there the timing sprocket is. When I say twisted, I mean that the part that the timing sprocket is machined on turned inside the weight it is pressed into.

The cheapest and easiest way to fix it would be to find a used crank somewhere and drop it in. You could also send the crank to a shop to fix it, and possible have it welded to prevent it from happening again.

I went with a used crank, and it took me a while to find a good crank with the correct teeth on the primary output gear (3 crankshafts exactly). Finally someone here offered me a good crank, and I was in business once again.

Here's a search on ebay:

http://shop.ebay.com/?_from=R40&_trksid=m38.l1313&_nkw=gs550+crankshaft&_sacat=See-All-Categories

Here's what mine looked like after I pulled it out


Maybe someone with more experience will be along to help. You might want to post in the parts section. Someone might be able to hook you up with a good one.

[mike_of_bbg]

I went with a used crank, and it took me a while to find a good crank with the correct teeth on the primary output gear (3 crankshafts exactly).

Aha! I'm sensing that this is not an uncommon issue then.

Oh, that's interesting to hear. They didn't keep that part consistent within the GS550 motors? I'd rather not buy crank after crank to find the right output gear. Is there some indicator as to what I'm looking for (# of teeth, direction of teeth, etc)?

Thanks for your feedback!

[Steve]

First of all,

BassCliff should be along shortly with his little 'mega-welcome'.

. I also notice at this point that the plugs are one heat range hotter than spec. So I'm fully expecting a couple of cooked valves now.

Please explain to me how a "hotter" plug will cook valves.
The temperature of a plug is entirely passive. That is, it sparks, creates the flame that burns the fuel, gets heated by that flame, then has to sink that heat away into the head. A "hotter" plug does not create more heat, it merely stays hotter because its heat sink path is longer, so it does not cool as quickly. It's entirely possible that the carbs might have been jetted too rich and "hotter" plugs were installed because they were fouling. In this case, I would expect to see valves coated with carbon, not burnt.

(it's really hard for me to believe that he could have taken it to a mechanic with compression that low in two cylinders and a suspect head gasket and said mechanic say it only needs a carb rebuild...)

Just goes to show you how much you can trust a mechanic. They may be "professionals", but if you look up the word, "professional" only guarantees that they get paid for it, not that they are good at it.

...two are too tight for my .0015" feeler... I have yet to find a local source for .01 mm feelers. Man that's a tight tolerance!

Let's be careful, here, you are starting to mix up your units. You started out talking about inches, now you're talking millimeters. Minimum clearance in millimeters is .03 mm. Either way, yes, that is a tight tolerance. Less than half the thickness of a piece of paper. There is really no need to actually measure less than .0015". The lower limit is about .0012", so if the .0015 does not fit, change the shim. By changing just one shim size, you will go to the upper limit of valve clearance specs or maybe just a tad over, but it's better to be just a bit loose than too tight. Toss me an e-mail (click on my name for the address) and I will send you a copy of my spreadsheet that helps you with valve adjustment and helps you keep track of your shims.

It seems kind of obvious to say yes, but would this timing cause the low compression #'s in those two cylinders? I mean, even with the timing off they still have to pass TDC with the valves closed toward the end of the compression cycle - albeit with a shortened intake cycle!

I agree with the others on the 'twisted crank' theory. Although your theory of a shortened intake cycle is plausible, remember that they might not be in sync with the cam. If the sprocket that drives the cam is on the same half of the crank as 3&4, pistons 1&2 will not be working as efficiently, so would have lower pressures. Enough to show what you got? Possibly.

.

[SqDancerLynn1]

It seems the 550s were prone to twisted cranks when abused, like their big brother 1100's. You take your chance buying used.

[seekinsoul]

It seems the 550s were prone to twisted cranks when abused, like their big brother 1100's. You take your chance buying used.

That does seem to be the case with the 550, and is the very reason I don't abuse it. It's also good reason to have it welded if your are going to run it hard. Finding a good one was a bit of a chore when I did it, but replacing it wasn't any harder than anything you would do while rebuilding the engine.

As for the gear, I think you just have to check your current crankshaft to see if it has the angle cut teeth, or the straight cut ones. Mine, as in the picture above had the angle cut ones. If you don't want to pull the engine apart just yet, pull off the clutch cover and look at the gear on the clutch. That will tell you what kind of teeth you have.

I also agree that you take your chances with buying used, so make sure what you are getting before you buy. It's hard to tell if a crank is bad or twisted from pictures. If you find one that may work, try to get a picture of it from the angle I took of my bad one, or better yet, try to check it out in person.

[BlackStar]

Sounds like your crank is twisted. I had the same problem when I got my '82 550L, good compression on #3 & #4, low on #1 & #2, etc. These cranks are made from pieces that are pressed together, and feature roller bearings instead of being one piece cranks with plain bearings. It's likely that the crank "twisted" in the center there the timing sprocket is. When I say twisted, I mean that the part that the timing sprocket is machined on turned inside the weight it is pressed into.

The cheapest and easiest way to fix it would be to find a used crank somewhere and drop it in. You could also send the crank to a shop to fix it, and possible have it welded to prevent it from happening again.

I went with a used crank, and it took me a while to find a good crank with the correct teeth on the primary output gear (3 crankshafts exactly). Finally someone here offered me a good crank, and I was in business once again.

Here's a search on ebay:

http://shop.ebay.com/?_from=R40&_trksid=m38.l1313&_nkw=gs550+crankshaft&_sacat=See-All-Categories

Here's what mine looked like after I pulled it out


Maybe someone with more experience will be along to help. You might want to post in the parts section. Someone might be able to hook you up with a good one.

Holy Crap that thing is twisted bad!!!

[850 Combat]

The gas in the oil is probably a clue. i once had a GS850 with abad petcock fill a cylinder with gas. it got a hydraulic lock when I hit the starter.

There is potential there to twist the crank.

My 850 ran for years after that. I always thought I could detect a little vibration though.


I sold that one in the late 80's.

[mike_of_bbg]

Thanks for the feedback. Of the eBay cranks I looked at, there was only one, from a 77, that had straight teeth on the output gear. All the 78-82's seem to be beveled like mine and yours, seekinsoul. I probably would never have looked at that though. We'll see how it goes. There's just a little bit more work left to get this crankcase apart, but that will have to wait for a while.