We hardly use the bike, but just so happen yesterday we took the bikes out to do some trail riding. After about an hour into our riding expedition, the motor started making a ticking sound. I shut the bike off thinking it was getting hot as we were just poking along. I happened to notice that the coolant reservoir was empty, so I filled it up and proceeded back to the truck. Before I could get there, the bike made a loud pop and hissing sound and died.

Today, I tried to restart the bike and noticed that there is water coming from what looks like the head gasket. I've never broke one of these bikes down, however I have rebuilt a motor or two in my day.

I know from what I've told you, we can't tell what kind of damage has been done until I get into it. However, it still feels like it has plenty of compression, so I'm hoping it will be nothing too major.

I checked the link here in the forum with the service manuals posted, but it came back as a dead link. Does anyone have another suggestion where I can get a breakdown and reinstall of a head gasket sequence? Also, any pointers would be highly appreciated.

I will also try to keep you updated of the progress as I go.

 

Cylinder head bolts torque in a criss cross fashion to 17-19 foot pounds. The 4 cylinder nuts torque to 24-28 foot pounds (or pretty snug as most people do). Once you added water/coolant to the hot engine and didn't bleed the 10mm bleed bolt at the top of the head you will blow head gaskets because of trapped air. Try Ebay ,etc if you have to as you really need a good manual on these engines. I wouldn't just try to replace a head gasket only! If it started making noise you probably have a piston starting to seize/lower rod problem and need to take the cylinder off to check it out along with the crank and rod bearings. OPT

 

Well, I started messing with the 400 today. I took a pic before I started taking anything apart, just in case this is the last time I see her together...lol



Plastics, seat and fuel tank removed.




Not that many miles on it considering it's a '97




The underside of the head...




Where the head gasket blew.




The cylinder wall, the piston and the head actually looks very good. I cleaned everything up, but forgot to snap some pics of it.

Since I never heard the fan come on, I jumped the fan wires straight to the battery and it works as it should. So now I'm thinking maybe a thermostat switch issue. I'll pull it tomorrow and place it in a pot of water with my meter hooked up to it to see if the contacts will conduct when it heats up. For kicks, I grounded the temp sensor and the light came on as it should (no buzzer if it's equipped with one).

Before I pulled the head, I turned it over with the pull rope and it still feels like it has a lot of compression. After seeing the piston and cylinder wall, do you think I still need to pull the jug off of it?

 

No buzzer,just a hot light! Once you pull the head,I'd pull the cylinder to at least mic the piston skirt's clearance to the bottom of the cylinder if the piston/cylinder doesn't look scarred.Clearance is critical. Can't tell by the pics,but looks like a stock piston.I'm old school! Once you take a cylinder off I can almost always find a reason to bore a cylinder to the next over size that will take any out of round,egg shape out. Nothing worse than putting a 2 stroke engine back together with the same piston and rings and then it seizes up! OPT

 

Being that this is my first bike rebuild, would I take the cylinder and head to a regular motor shop to get the work done or is there a special shop that strictly deals with bike motors??

 

Most good cycle shops can measure the cylinder,tell you what oversize is needed and can bore the cylinders out for you. Better to be safe than sorry since you have the head off anyway. OPT

 

I found a recommended machine shop that will do the cylinder boring and check the head to make sure it's not warpped for me today. They asked that I bring the new piston in with it. Being that I need to order that first, after a little research, I'm going to purchase the Wiseco brand piston kit with a new top bearing. Now my question is, what size do I order? Is there a way to check and double check the old piston that's in the bike now? Hopefully under the gunk ontop of the piston, it will have some markings on it. Also, being that the standard is 83mm, should I go up .25 or .50? It does have a few marks in the cylinder, but I'm not sure if they will still show up if I went with .25 bore.

I would hate to have to buy two pistons for this thing.

Again, I'm not into the high performance racing scene. I use the bike to trail ride and during hunting season.

 

Sounds like the shop is getting the cart before the horse! You really need to measure the cylinder first to determine what oversize is needed to clean up the cylinder! Just from looking at the pics and if there is no great scoring in the cylinder,first over(.25mm) (.010) should suffice,but again have the cylinder measured against the stock 83 mm bore! Then a Wiseco complete kit(piston,rings,bearing,pin,clips,head and base gasket) is the best way to go,then they can bore it for you. OPT

 

Okay,
After your advice, I pulled the cylinder off this afternoon and I'm glad I did (thank you). I was telling one of my coworkers that I was breaking the motor down and he suggested that I take a look in the crankcase when I pull the cylinder. He told me that if it's full of water, then the seal on the back of the water pump is probably bad and will need to be replaced. Well, the crankcase was full of water, so maybe this is what caused the whole ordeal to start with. Since I have it down this far, where is the water pump located and should I put a new pump in or just changed the seals?

Here is the motor with the cylinder pulled....







A close up of the piston. Again, thanks for talking me into pulling it.

 

The water pump is behind the flywheel and stator enclosed in the engine. Doesn't look like 1st over will clean it up,probably have to go to 2nd over piston. Coolant came most likely from the blown head gasket.I had this happen quite a bit!!The major thing besides the piston is to make sure the rod and crank bearings are ok (I would not do a top end only for this reason!) Here's breakdown of what's in the engine. Best to have a manual to work on this as it's a complicated engine. http://www.cyclepartswarehouse.com/f...1997&fveh=5430
OPT