1981 XS400 Engine Build: A Story of Pictures, Videos, Beers & Tears

[burr]

Hey Everyone!

After hijacking a few threads, I figured I'd start my own. I'm rebuilding my 1981 Yamaha XS400H (4R5 engine). It's my first bike. I'm pretty mechanically inclined but I've never worked on anything like this before. Here goes nothing…

A Little Intro:

• Bought this guy for $600 CAD in Toronto.
• It had ~14,200 miles, or 22,900 km
• Carbs were sparkling clean (PO had ultrasonically cleaned them)
• It ran OK.
• At a shop, I got the air filters replaced, brakes "tuned up" and oil filter changed. They installed a new Battery.
• Put about 500km on it (300 miles for our Americans) over the course of 10 days.
• I was hearing some clicking in the days before it happened. I now believe that was poorly adjusted valves.

Then, just 2 minutes from my house, it happened; a sickening crunch, 'tick-tick-crunch-tick-click' and a puff of noxious smoke appeared. A sound you'd expect to hear when knawing on Kashi cereal and simultaneously eating poprocks. That deep-in-your-bones feeling when you hear a sucker punch on Worldstar and the sickening crack of knuckles against skull. It was also impossible to miss the aroma of white smoke and hardcore burning plastic, like accidentally leaving plastic tupperware on the stove overnight.
The result was I completely lost engine power. Wouldn't start. No resistance from kickstarter. Electronics seemed OK. Didn't want to shift into 1st gear from neutral. Seemed like it would shift into 2nd, 3rd etc.

Great. A total write off, I thought. The foretold and forewarned 'deal-too-good-to-be-true'. But all was not lost. For I had picked up a semi-complete spare XS400 engine, and had a multitude of parts.

This thread will chronicle where I started with my Barney (The Purple Dinosaur)–coloured ride. I promise to upload only the highest resolution pictures. I will start a YouTube channel, packed with questions, frustrations and updated tips as I go. Disassembly vids? Yes. Reassembly vids? Certainly. Tuning, adjusting, cleaning pics and videos? You bet. Anything and everything to please you engine-porn junkies

In the month or so since I've owned the bike, I have learned countless details from this community. I want to give back. But I need some help. Lots, actually. The only thing I ask is… be my Obi-Wan Kenobi. You're my only hope.

 

[burr]

Here's where I started from. It was gross, but I was happy. The first thing I changed were the handlebars. That was pretty easy; the original handlebars were quite long, and the new clubman style ones were quite short which means I ended up with quite a bit of extra cable length. Also, I'm a pretty tall guy, and needed the extra reach so I dealt with it.

Tribulations #1. A driver backed into the bike, and left the tank dented, the left rear light broken off, and the paint really damaged quite badly. But he left a note, and gave me cash. I didn't ask for much, because I figured I'd be stripping it anyway.

Did I mention I made a custom seat? I'll definitely be posting all the steps and materials required for how I did that.

• Uses the original seat pan
• 3 types of foam
• marine-grade vinyl
• Only cost about $50 CAD to make

I think it looks unusual, unique and Holy Gary is it comfortable. Gives my Ogre-sized body some extra height, too.
These pics here show the condition I got it, and the first two upgrades I made.

 

[burr]

So, the 'kerplunk' noise of the event meant I had to get my hands dirty very early into my bike's life. I always wanted to rebuild. Careful what you ask for, right?

Anyway, the first diagnosis I did was non-instrusive. I removed the left sparkplug and peeked into the cylinder…

Three pics, one video: The left sparkplug was badly smashed. The right sparkplug look pretty white. The left piston looked heavily damaged, from what i could see when I used a flashlight shining into the sparkplug hole. (Anyone want to comment and gives me tips on the right sparkplug? Is it within reasonable limits of whiteness?)

 

[burr]

The current stage I'm at is a complete disassembly of my backup, "spare" engine.

I've broken down the top end completely (rings out, cylinder heads out), gear assembly out… my question now is what is the best method to completely clean the grease off the disassembled internal engine components?
Do I soak them in mineral spirits? Do I spray all the parts with a degreaser, pressure wash the degreaser off, then re-lube them with engine oil?
I have the the degreaser spray 'Gunk' brand but it wasn't too effective.
How do I treat the bearings, like the needle bearings on the gear assembly? Do i soak them in a degreaser as well? Let them be and just coat them with engine oil when i reassemble?

Also I'm not too concerned about the looks of the external cylinder yet, but should I coat everything in aircraft/marine paint stripper before I rebuild?

Here's what I'm talking about:

 

[NewHavenMike]

I think I used a spray bottle and mineral spirits, along with a pail of mineral spirits to dunk parts in..

I had a oil tin to get the parts covered up fast. Bearings, I kinda didnt touch them because when I tore my bike down, I took off what I needed to and closed the case back up, I made sure that everything was in working order and dumped oil on everything and then put a plastic bag over the top. It stayed like that for around 6 months..
I used this type of gun oil called, EEZOX, it came in a small flip top tin. My machinist that bored the cylinders warned me about flash rust and it needs to be assembled fast or constantly oiled, which I had already known. But I used this oil and I left the cylinder jug in a box in my room all Winter and there was no rust at all..

 

[arfstrom]

The manual is going to be your best friend for this. If you haven't already looked, I use a chiltons. I have done this 3 times since 2010, and the middle time, I took the jug's to a powder coater, and had the jugs/sides coated with a nice black paint. (case I just rattled canned it.) I recently used a nylon long bristled to try to clean my fin's, and carbs from the winters accumulation of dust. my first time working on this, I made a decent relations with the local Yamaha maintenance guy, at the dealer, whom was very informative on what to do. since I needed parts, and the parts guys have some clue. (their background varies)

Thanks for taking photos, So what was the issue? Piston? cam chain?

 

[burr]

Woah buddy… I've got some good pictures for you guys! Be cautioned that these pics are NSFW, it's pure piston GORE.

Today I finally removed the engine to diagnose the real problem, rather than just shining a light through the sparkplug gap. As promised, HQ pictures.

To remove the engine I pretty much followed the instructions in the manual. I did a couple things differently, so I'll mention the issues I faced and how I dealt with them. (Anything I don't specifically mention should be the same as Pg. 52 in the manual).

1. Electric Starter: The starter chain was very easy to remove. No issues at all even though it was filled with muck and grime. There was even a full leaf that was still kind of green! I chose to remove the entire electric starter from the engine case, instead of disconnecting it from the frame and assembly Took a bit longer, but no big deal.
2. Drive Chain: the drive chain and sprocket were also easy to remove. I used a screwdriver and gently tapped with a hammer to 'pry' the bent washer tab behind the drive sprocket flat. My sprocket nut (~30mm size? It's big!) was finger tight. I didn't see any specs in the manual for specified torque/tightness, I hope this was ok. Once the large sprocket nut was unscrewed, I wiggled the sprocket off and the drive chain was easily disengaged.
   • I was worried about removing the chain, but it turned out to be VERY easy. No special tools required, even though the manual mentions that you may need a special 'chain cutter' tool. The tools I used were: a hex/allen key to remove the cover, and a screwdriver+hammer to bend the washer tab. That's it!
3. Engine Mounts: The manual was not clear on removing the engine mounts. In fact, it said you had to remove the rear engine mount bolt from the right side. Untrue. I had to unscrew it from the left side, and pull it out with pliers from the right side. Also, whoever assembled this bike was an idiot, and had stripped a few of the front frame mounting bolts. That's fine, I just removed those mounting plates from the frame rather than remove the engine mounts from the plates (Hope that makes sense). Overall, not hard to do – I was surprised how few screws hold the engine in place.
4. Engine Removal: What a PITA. The manual says you need to remove the oil filter before removing the engine. However, I wasn't able to remove the oil filter; the PO was clearly an idiot and had stripped the hell out of the oil filter assembly screw head. He had then tried to chop it with a dremel in order to use a flathead screwdriver, but cracked it. Even with an impact driver I couldn't unscrew it. Damn… so I tried something else. I was able to remove the engine from the frame WITHOUT removing the oil filter. By first removing the Valve Cover, cam, and cam sprocket while the engine was still in the frame, I was able to gain extra clearance and lifted the engine free. Here's some pics of the bike + oil filter screw all messed up.
   • Also, the ignition points cover was installed with two screw, one of which was stripped. When I removed the ignition points, i noticed it doesn't look like the one in the manual or in other pictures on the forum. Can someone tell me what is going on with the points i removed? Are they even a "points" ignition? Pics below. I found an identical part on eBay but it's called "Pulser Pickup & Rotor, part# PU264-01."

 

[burr]

Once i removed the engine, I got to work taking apart the top end. I already had the valve cover off and a piece of string tied around the cam chain. I noticed a slight burnt smell from the engine.

As I unscrewed the acorn nuts from the cylinder head I noticed one of them was murderously tight. Eventually i got it off by retightening the other nuts, but was greeted with an even fouler smell. You gotta see the pics, I haven't seen anything like this on the XS400 forum yet.

Inside the Cylinder: Now for the fun. The left piston head was completely melted and looked like a crumpled mound of aluminum foil. Actually, it looked like the foil wrap around my turkey sandwiches I packed for lunch a few days ago. Seriously, WHAT IS GOING ON?!?! The exhaust and intake valves on the left side were also completely destroyed. The valve cover is chewed up, not to mention the valve seats are gone. Everything on the left side looked like it was raided by Attila the Hun double wielding scimitars of damascus steel. There is small bits of shrapnel in the left side of the carburetor near the butterfly thingy, too. I didn't take pictures of the carbs, but they'll need an overhaul, too.

• I read on another thread about things that cause melted pistons… @16VGTIDave mentioned in this thread that air pods directly on the carbs (i.e. without a rubber H-Pipe) can cause problems. My bike did NOT have an H-pipe. The air pods were strapped onto carbs using one pipe clamp and rubber housing. I should have taken more pictures, I will in the next few days.

Inside the Cylinder Jugs: Once i pulled of the cylinder jugs, I realized the piston connecting arm was mangled. See the pics, it's pretty gruesome. I didn't have time today to split the crankcase… that's for this weekend.
So, now the plan is: split the crankcase i just pulled out and figure out the extent of the catastrophe. Seems like part of the piston connecting arm broke (or rod? leg? What's the proper term here?). Could also be the crankshaft or crankpin that fractured.

The Engine Case HOLE: Beneath the electric starter I noticed a hole. It's definitely not supposed to be there… I will investigate further when I split the crankcase. Any bets on what caused it? The engine case must have taken pretty savage blow. I did not notice any damage to the electric starter itself. I'll upload a video on Youtube soon.

 

[burr]

Also, during my engine removal I found these two pieces on the ground when cleaning up. I'm unsure of where they came from though.

Does anyone know what these two parts are for? The one with spindly legs feels like aluminum. The round one with letters and a directional arrow has a softer rubber inner bit. It's very lightweight, and might be plastic. They are both of similar diameters, maybe 30mm or so. Thanks

 

[arfstrom]

The two pics are of the bushing that goes to the rear motor mounts. The other one appears to a seal from the case, perhaps the clutch rod seal. (or one of the other 3 thats on the case) perhaps PO used it as a buffer on the rear motor mount too?

Part 19 on this diagram
http://www.partzilla.com/parts/search/Yamaha/Motorcycle/1981/XS400 - XS400H/FRAME/parts.html

 

[xschris]

Get another motor!!! That one is done. Use what parts you can from the old one as spares.

 

[burr]

Thanks @arfstrom ! That makes sense

 

[NewHavenMike]

Yea that thing is TOAST.. You may get lucky and have some good transmission gears to save.

Looks like a valve dropped.. Maybe from revving too high?

 

[burr]

@NewHavenMike How does revving too high make the valve drop? Also, Why do you say this is a valve drop? The valve was damaged, true, but still in those cotter pins in the valve cover. For what it's worth, the sparkplug was all smashed up, too.
Regarding revving too high – I liked to throttle blip/engine brake (for the short time I used it, only about 600km/350 miles). That definitely increases revs. Still unsure how that's bad though.

 

[Tyler Shiells]

@NewHavenMike How does revving too high make the valve drop? Also, Why do you say this is a valve drop? The valve was damaged, true, but still in those cotter pins in the valve cover. For what it's worth, the sparkplug was all smashed up, too.
Regarding revving too high – I liked to throttle blip/engine brake (for the short time I used it, only about 600km/350 miles). That definitely increases revs. Still unsure how that's bad though.

Your missing the exhaust valve on the left combustion chamber. Or did you take it out?

And to get all those parts up here in canada is going to cost prbly as much as parts bike you may find.

I just replaced the rings and valve seals and all new gaskets and that cost me about a $140.

 

[NewHavenMike]

Well, These engines are made to rev pretty high but it could happen still...

The valve retainer/lock could just become unseated in the retainer and that will cause disaster. If it was your timing chain, both cylinders would probably have messed up valves.

Valves were probably floating and things got knocked loose. The action of a valve train is pretty sloppy, youtube some videos of valve floating and youll see.
These engines are also pretty old and most have a ton of miles on them.

 

[BBS360]

Wow. Just wow.

Not just holed but chewed up inside.
I'm wondering if the engine kept running on one cylinder for a while before the con rod blew off? It'd explain all the additional damage to the piston and the noise you mentioned.

 

[burr]

Yeah - I removed the valves on the left side, both intake and exhaust.

I have a second engine already, the plan is to swap out the entire top end from the current busted-ass engine with the "backup" engine. But considering the hole in the top half of the crankcase of the busted one, I might be forced to use the entire backup engine. I'm hesitant to use the backup because some of the screws are stripped – such as the ones holding in the circular gear change thing on the right side (not sure what it's called).

 

[burr]

@BBS360 It must have continued to run, right? Spinning the cylinder manually via the stator would not have caused attrition like this

 

[BBS360]

Pretty impressive really. If not for the con rod busting apart it might have kept running for a while.

Circular gear change thing? Right side? The clutch plate assembly?
I'd use the complete spare motor. Invest in a manual impact driver to help bust out screws. Some seafoam deep creep will help loosen them up.