top-end troubleshooting redux

Hm. So I double-posted, edited the later double post to say sorry, and then the original post was deleted. So here I go again. It was a long freakin' post, too. Let's see if I can remember it.

Background: I bought a 1982 KZ550C3 with 13k on the clock last fall to have something to ride as I try to restore my 1975 Yamaha XS650. I bought the basket case 650 two years ago with little riding experience because I wanted something to work on, but then, after the MSF course and riding around other people's bikes, I wanted something to cruise around on. Hence, the "working" KZ550 I picked up.

When I test-rode it, the 550 was already warmed up. It also had expired tags. Both bad signs, which I overlooked. Now I know. Bike seemed okay, maybe just needed a little TLC. All four pipes were hot.

When I returned, I couldn't get it to start for the life of me but for a few times. Power was poor and the bike would bog down under throttle. I tried a few things, but it got cold & dark out, and I have no garage, so it sat for the winter.

Spring has come and I have been trying to breathe life back into the beast. You've probably seen some posts on the matter. But I think I may have found the source of most of my woes.

Symptoms: Poor startup (won't unless I use starting fluid), "clunking" noise, especially when cold, at idle. Bogs down when throttle is applied. Sometimes, even when warm, it wants to die as I release the clutch and go into first, even if I give it a decent amount of power. Also, sometimes, when it dies, it sounds like the starter gets kicked over once.

Last year, according to my notes, #1 and #3 pipes were cold (lukewarm). This year, I found that #3 could be cool. Plugs (new) now have shiny, oily black electrodes -- not fouled, but probably getting there.

I replaced the battery. 11.8V at the coils, 12.3 at the battery.

On Friday the 13th, my compression test adapter finally arrived. It was a bad omen. Here are the compression results when warm (1, 2, 3, and 4, psi):

110 90 110 170

Yesterday, I added a small amount of oil through the spark plug holes. The compression was then:

160 125 175 230

These are steady state values after several cranks Based on a compression ratio of 9.5:1, I would think this should be 140.

I checked the valve clearances a while back. These are:

exhaust: .012 .010 .009 .007
intake: .005 .006 .007 .006

My Clymer says that exhaust should be .006 to .010, and intake .004 to .008. So, with the exception of #1, these are in spec.

The oil tells me that the problem is worn rings / cylinder walls, though the high compression of #4 worries me and makes me think valves have something to do with it. So this is probably a top-end rebuild and not just a valve job.

Now, the questions:

- Is this the correct diagnosis? I haven't done much with carbs other than check float level. From what I can tell, all four are firing. (FYI, yesterday, when I fired after dumping oil in the cylinders, #1 was cooler, so it seems to be jumping around.)

- I only see rings & pistons for sale at bikebandit and not z1. Any other sources? If I get the cylinders bored over, do I need new pistons, or is it possible to just get larger rings?

- What are the other possible contributers to my problems (clunking, poor starting, etc.)? Do I have to worry about anything in the bottom end? Is this time for a whole rebuild?

- I bought the 650 for a rebuild and the 550 to ride. A rebuild after 13,000 miles sounds excessive. If I have to rebuild the 550... you may find a parts bike for sale shortly. What is going to be involved here?

Thanks for the comments.

Nick

Post edited by: nick_borer, at: 2007/07/15 17:44

nick_borer wrote:

Now, the questions:

- Is this the correct diagnosis? I haven't done much with carbs other than check float level. From what I can tell, all four are firing. (FYI, yesterday, when I fired after dumping oil in the cylinders, #1 was cooler, so it seems to be jumping around.)

You might be jumping the gun a little, it does have a problem but I don't think you can definitely say it is the rings at this point.

- I only see rings & pistons for sale at bikebandit and not z1. Any other sources? If I get the cylinders bored over, do I need new pistons, or is it possible to just get larger rings?

If BikeBandit (that's an honest name) can get them, then so can Jeff at Z1 Enterprises, you just have to ask.

If it is the rings, then it's doubtful that you can hone the cylinder and still be within service limits for a standard piston (but you might get lucky), so you would have to get new pistons and rings. At that point, Wiseco big bore kit becomes a cheaper solution, 615 cc for a 550 I think.

- What are the other possible contributers to my problems (clunking, poor starting, etc.)? Do I have to worry about anything in the bottom end? Is this time for a whole rebuild?

I did a compression check on a 750 four recently, 70-90 psi cold on all four, added one sqruirt of oil to each cylinder and all four shot up to over 200 psi. That's bad rings

It is possible that you have valve sealing problems, and worn valve guides. A leakdown test would narrow it down to the actual problem.

Personally, I'd take a look at the bottom end before deciding to fix it, there comes a time when it's cheaper to just get another motor (probably around $200 or less).

- I bought the 650 for a rebuild and the 550 to ride. A rebuild after 13,000 miles sounds excessive. If I have to rebuild the 550... you may find a parts bike for sale shortly. What is going to be involved here?

Leakdown test

clean your carbs. The cold cylinders are not getting fuel. The clunking is probably from the kicking in and out, mine does this when its not running on all 4.

Were the compression readings done with the throttle held open? Was the bike warm or cold?

It's going to be dirty carbs from sitting. gas will turn into a nasty gummy mess when it is allowed to sit in the carb bowls for a while. This will clog all the passages and jetting.
You need to take the carbs apart and CLEAN THEM REALLY GOOD. I bet most of your problems will go away.

Compression done with throttle closed, good point, shoulda done it with throttle open. When I get a chance I'll remedy that and repost the numbers.

The first set of values (before I added oil added to cylinders) were with the engine warm, though I got the same readings (within ~5 psi) cold. The second set was the next day, and the bike was cold.

Carbs are next, for sure, but if compression isn't up to snuff then I need to figure that out for sure. I really hope it's valves, but the oil makes me think it could be rings or worse. Of course, it could be everything...

Regarding carbs, the bike sat during the winter with the carbs drained & off the bike. However, I'd be willing to bet that it wasn't used much in 2006 before I bought it because it still had '05 tags. So yes, there could still be varnish & other badness in there. For the record, the bowls were removed and everything was fairly clean. I also dumped in a little bit of fuel system cleaner into the gas as I was running it last year, and the gas I have (stored in a separate container all winter) probably has some of the cleaner in it. I know that octane gradually decays over time; I used premium so I would doubt the gas is a problem. The evidence of poor running should be sealed with the compression test.

Now I just need to steal some time away in the evening to do a proper compression check. One question: a compression ratio of 9.5:1 should yield about 140 psi of compression. Shouldn't I be worried about 170 and higher? That could lead to preignition on #4, yes?

The rings sound like they are stuck. That happens from sitting.
They will get better once the bike is running.
You CANNOT clean the carbs by pouring in "fuel sytem cleaner" you have to take them apart and clean them by hand. PITA but it is the only way.
Once you have the carbs cleaned and back on check the valve clearances, put in new plugs and make sure the points are clean and working properly. Get a good charged battery then pour a little oil into each cylinder and try to start it.

:quote:These are steady state values after several cranks Based on a compression ratio of 9.5:1, I would think this should be 140.

You would think so, atmospheric pressure (at sea level) of 14.69 psi X 9.5 = 139.55. Of course thats assuming a volumetric effciency of 1, not likely at cranking speed because of valve overlap and ring and valve leakage. Also if someone replaced the valve core in your compression tester with one from a tire it will read way lower than with the correct valve core. (ask how I know this :blush: )

Post edited by: Z1R rider, at: 2007/07/17 19:54

nick_borer wrote:

I also dumped in a little bit of fuel system cleaner into the gas as I was running it last year, and the gas I have (stored in a separate container all winter) probably has some of the cleaner in it. I know that octane gradually decays over time; I used premium so I would doubt the gas is a problem.

It might be ok but personally I would'nt trust it. Every winter I put Stabil in the gas tank while the bike is in storage and every spring I empty that gas into the van and use fresh from the pump. One less thing to cause a problem.

I would check compression using the proper method and adjust the valve before moving forward with ANY carb adjustment which will more or less be a waste of time if any valves are hanging since that affects compression and thus, vacuum. An engine is an air pump... some issues MUST be resolved and made correct before moving to the next if you are trying to resurrect and old bike. If you fail to do this and approach things randomly, it can be frustrating.

I wouldnt worry about the noise, When my bike wasnt firing on all four it souded like it would come apart.
Do a comp test the right way and go from there.
Either way you will need to clean the carbs, and lube the advancer. I think you might be jumping the gun a little:) Take your time and dont rush.

I wouldnt mess with the valves till you get it running on all four.