Newbie with seized engine

[carld]

Hi everyone, I've just recently acquired an XZ400 as a non runner.  After cleaning the carbs out real well and repairing the YICS, it started and ran without problems, but I never ran it more than 10 minutes at a time as I hadn't registered it yet.  Also, I heard strange knocking sounds in the engine and didn't want to push it. 

After doing some research, I found out the knocking was due to the starter clutch so I drained the oil, opened it up, fixed the clutch (loose bolts as promised), closed her up and put in new oil.

Thinking everything was okay, I took it on the road to have it registered.  It ran fine for the first 3KM or so then started to lose power and finally died.  While it was coasting, the bike was left in gear, on the off chance that the bike would jump start, which it didn't. As the bike slowed down to almost 0kph, the rear tire suddenly locked up.  As I thought it was nothing, I tried to start with the starter button but no dice.  I also tried to push start in second to fifth gear but every time I popped the clutch, the rear tire would just skid.  After towing the bike back home, rocking the bike back and forth reveals that the engine may indeed be seized.

Any ideas on the cause?  I had just put in new oil, water was good, no overheating, bike ran for less than 15 minutes.  Am I going to have to take the engine apart or is there something I can do externally to get it running again?

Thanks in advance! :)

[Walt_M.]

That sounds like a dropped valve, but I haven't heard of that as a common XZ problem. It could also be a spun rod bearing. Easier to check the valves first though. Good luck.

[YellowJacket!]

Sounds like something either came loose during one of your repairs or may have been left in there and got stuck.

David

[xswheels]

Do the easy things first. Remove your spark plugs and check them for debris and colour. Since you had your engine cover off prior to the seizure, I would pull that cover and look for missing/loose bolts or any damage.

[treedragon]

Here in NZ there are/were a lot of the 400's and they are notorious for trashing the rear main with a large number going through the bike shop I deal with. Coincidentally yesterday my engineer friend there was showing me an XZ final drive shaft that had been converted to chain drive and pointed to the oil feed hole in the end of the shaft and commented that it was the reason the 400's kept on trashing the rear main............

Quote "It's a design F***up, the 550's have a lot smaller feed hole for the drive shaft lubrication so no problems. Under stress the 400's just don't get enough oil." With him being an XZ engine fan(atic) the problem bugged him for ages until he spotted the difference between the two models.

[carld]

Thanks for the replies guys.  I'll do the spark plugs and side cover first to check for anything loose and for damage.  While I'm in there, I'll see what wiggles and what doesn't as well.  I do hope it is nothing serious.

I'll be bcak with updates. :)

[Rick G]

Also, re check your work in the starter clutch. Any time I work on a bike and it immediately  develops a problem , I re check what I have just done . it pays to be sure.

[carld]

Well, the starter clutch was a rather simple repair so I do hope I didn't mess it up.  But then again, it wouldn't be the first time I messed up something simple. :D  Thanks! :)

[carld]

Hi Everyone, just an update on my XZ400.  I've been out of the country quite a bit lately and I haven't been able to mess around with the bike.  I finally took it to a mechanic last week to have it taken aprt, as I didn't want to dig into the engine and I suspected it was something deeper.  It looks like Walt nailed it with the spun rod bearings.  I'll be going to get some replacements and hopefully all will be well afterwards.  The rest of the engine seems to be in great condition though. :)

Cheers.

[Rick G]

I hate to pop your bubble, but if it has spun a rod bearing, it will need a crank shaft. Yamaha provided no under size rod bearings.
D. Minor  has used rod bearings from a 1983 Mazda 1500 (actually a little over that like 1585, or there abouts) and had the crank reground . A Visionary in Scandinavia also report getting the crank reground,  and using Japanese car, rod inserts
I'm working on it, as I want to have a spare.

[carld]

Thanks for the heads up, Rick.  I found that out the hard way when I went hunting for parts yesterday.   ;D

No problem though.  I found some inserts from a Nissan (possibly a Sentra) that are almost the right size.  The inside of the conn rod where the bearing sits will have to be built up a little and the crankshaft ground down a bit. I got the oversize 0.75 just to be sure.  The inserts have to be modified though, a new lubricating hole needs to be drilled in to match the conn rod hole and it may have to be trimmed slightly but it should work.  I've got a machine shop working on it for me right now.  Apparently this sort of thing happens a lot here in the Philippines where original parts are hard to come by.  The machine shop knew exactly what needed to be done.  ;D

[carld]

Well, I got news from the mechanic yesterday that the engine is already up and running.  They just need to button up a few things and I may be able to take the bike home today.  The mechanic warned me however that on these bikes, once the crankshaft has been repaired, that's the start of all the problems of this bike and it would be best to offload it already.  I was wondering how true that is and if I should take his advice to heart.

I'm generally handy with tools and I can fix almost anything on a bike external to the engine, but to be honest, I know zilch about internals.  When it comes to the engine, I always say if it ain't broke, don't fix it.  If I'm going to have a problematic engine, I don't know if I will be able to keep it running.

The flip side of that is, now I have the perfect opportunity and excuse to learn....

What do y'all think?

[Tiger]

 :) On your travels, keep an eye open for another motor that you can mothball and keep as a spare...just in case ::) I have three ;) I really wouldn't worry to much mate...

               8).......TIGER....... 8)

[carld]

Hi Tiger,

Thanks for the reply.  So you think I should keep it? Even if it's a 400 and not a 550?

[Rick G]

Spare engine is good advice , even better, pick up a couple of spare bikes.
If they did there work properly there is no reason to sell the bike. You could also keep your eyes open for a clean 550./
What you described was a classic case of spun rod bearing.

[carld]

Well, that's comforting to know. :) I don't know if I can find spare bikes though, or if the wife will let me keep so many spare parts around (I already have 5 bikes including this one).  ;D  I would actually like to keep this if it's worth it, I already had plans for the paint and all. :)