1990 Zephyr 550 Project

Just the cap bolt that threads in at the end of the tensioner? That’s happened to me before. The original tensioner is… not great. 

If you can track one down, get the later model tensioner. I know I’ve posted about it somewhere else here on the forum, might take me a little while to find the post and part number for you. But it’s a way better tensioner that is much more intuitive to use. People will tell you to get a manual one, but you’ll end up having to adjust that, well, manually, and with the tight space behind the engine on these bikes it’s a huge pain in the #$$. 

Edit: here’s the thread:  www.kzrider.com/forum/2-engine/621445-ea...changeability#910178
it looks like I never followed up on it, but I ended up getting the later model superseded part and it works great. The best part is that when you are checking timing you don’t pull the whole thing out, just the spring. So it stays where it was, without the risk of it expanding further, and after you check timing, you put your cam cover back on, reinstall the spring, and you’re good to go. 

But also if you decide that a manual tensioner is what you’d prefer, I have one that’s yours for the cost of shipping. 

Yes, it was just the cap bolt that stripped out.  Thanks for the information about the tensioner, I went ahead and ordered the updated/later part. I did a leak down test(glad I did), cylinder #3 exhaust valve is slightly bent.  I pulled the head and have a new valve on order. 

I've had a manual tensioner on a KLX250SF back in the day, it was more of an annoyance than anything. I like the set it and forget it of automatic tensioners. 

Here are pictures of the scoring on the camshafts.
     

The used cylinder head I bought has several leaky valves, I set it off to the side. New exhaust valve installed into the old head, reassembled and put back on the bike.  Valve clearance was loose, intakes all over 0.32mm and exhaust all at 0.50mm or more.  The cam chain is at the edge of the service limit.  New front(it had a 17t) and rear sprockets(39t was on it) installed, new rear tire to replace the oversized one on it.  I removed the swingarm to check the bearings out, they're fine but there was very little grease and the seals are done. I am waiting on parts from Japan because surprise, you can't find them in the USA. 

 
 
 
 
 

 

So that is probably the last iteration of the early 1980s GPz550 engine, of sorts. I wonder if it shares any parts with the old version?

The engine has a blown bottom end, I think the oil control rings on cylinder #2 and #3 are broken.  It spit tons of oil out of both cylinders and I couldn't see a foot in front of my face after running it for 30 seconds in my garage(door open).  It starts right up, revs fine, no hesitation at all, but has piston slap that sounds like a diesel and would explain the abnormal cylinder wall wear I saw. So now I I need to source a new engine, I don't want to continue to fix problems the previous owner did with this one considering all of the RTV I found inside of everything.

The bottom end is completely done on this engine, the rod bearings have a ton of vertical and side to side play.  There is no way the dickhead who sold me this bike didn't notice that when he split the case and reassembled it. So much wasted time. 

Sorry to hear that.
An acquaintance of mine has one of these also, and his bottom end is also blown. Shame too, because otherwise his bike is tastefully modded and in showroom condition.
Makes me wonder if this might be a common problem on these bikes, and I should be doing some kind of preventative maintenance to make sure it doesn’t happen to mine. 

Small engines are very robust. For things to get to this point, there must have been a lack of lubrication. Oil pump failure, lack of oil... there could also have been gasoline in the oil, due to a problem with the fuel tap. The Zephyr and GPZ engines have many compatible parts; the Zephyr is a GPZ550H. Only the external appearance is different. After taking measurements of the crankshaft, install new bearings, and you're good to go. Be careful with the pump.

The project is still going but I may end up just getting rid of it as a roller once I get around to splitting the case.  New fork tubes, previous owner crushed them in the clamps and the spring wouldn't move despite saying he rebuilt the forks(he just threw on new dust seals and they were out of oil).  New OEM bushings and seals were also thrown on the forks.  The lower steering bearing wasn't pressed on the stem completely, it's like he gave up trying to change it out after gouging the hell out of the steering stem trying to remove the race.  I filed that down and got them changed out the correct way.  Front tire(correct size) is new along with the wheel bearings.  The only motorcycle I am buying after this would have to be a new one from a dealer, problem after problem just due to incompetence and being a lazy person on this bike.   

 

 

That’s a shame. They’re great bikes, and I hate to see one so abused. I don’t know what compels some people to try to do maintenance or mods that they clearly aren’t capable of. I mean I say that  as someone who has definitely gotten in over his head on things a few times, but still. 
I really hope you’re able to see it through and get it up and running yourself. You’re clearly qualified to do it. But if you decide to sell it as a roller, I hope the next guy keeps this thread alive and isn’t a hack. 

Come on, let's not get carried away. We need to sit down, list the cost of the repairs, and ask ourselves these questions: Do I want to go? Is it worth going? Should I go? It's difficult to form an opinion until the engine has been disassembled and inspected.