Thanks to Murray (MUZ)

With Thanks to Muz, Without Whom This Would Not Be Here

Saturday, January 14, 2012

GT380 - Oh Oh this is not good.

As I wrote in the previous post, the crank is tight in the cases and No1 appeared to be damaged in some way. So I removed the pistons and split the cases. When I split them the crank stayed in the upper case which is unusual.

The crank was tight in the upper case and wouldn't rotate. Further examination showed that rod No1 was bent.

I then had a closer look at the piston, It was broken and cracked internally.

When I split the cases I observed a lot of oil sitting in the bottom of the crankshaft area. This was unusual but I didn't think much of it at the time.

Looking at it now it seems that I had a case of 'Hydraulic Lock'. I don't know how the crankcase filled with oil. The only thing I can think of is that the oil tank contents had bled slowly through the oil pump and feed pipes and had slowly entered the crankcase over the many years of storage. Then when I've started the engine it has run briefly before enough oil was forced up through the transfer ports into the combustion chamber to fill the chamber with more oil than it could hold. As fluids can't compress the piston has travelled up and at a certain point could not travel further and has come to an extremely rapid stop. The inertia of the crank etc has then caused the connecting rod to bend and the little end to break the internals of the piston.
As can be seen in the above photo the rod has quite a large bend in it. The little end bearing and pin are probably damaged as well.

So now I'll have to get the crank rebuilt. I only need one conrod however they are generally sold in threes and are quite expensive. I'll shop around. I should be able to get a single piston and the bearing. Then I'll have the crank split the new rod installed and then the crank rebalanced. Hopefully then it will all go back together and run ok.

GT380 Engine Removal

I pulled the engine out the other day. I am very curious as to why it stopped.

First I just removed the head, carby's and exhausts to see if I could see what had happened.

No luck so it was off with the oil supply for the pump, electrical plugs, clutch cable, tacho cable, chain and engine bolts. Then onto the bench.

Still couldn't see anything so off came the cylinders.

Now I was getting somewhere, No 1 piston was not moving freely and its rod would not move. No's 2 & 3 were free. I was running out of time so I'll do the rest tomorrow.

Sunday, January 8, 2012

GT380 Carburettors

I have settled in at the new location and have finally got a bit of time to address the GT380. The last post was about the leaks in the fuel tank. I put a liner kit in it. I did take photos and documented the process however in the move I seem to have lost the photos. If I find them I will post them.

Anyway the kit worked well, the tank is fuel tight. The fuel tap has a leak and I must get a kit for it (if possible). When I cleaned the carbys there was a hole in the fuel bowl of the middle carb. I was unable to fix it properly, I made a temporary fix for it. It held fuel but did weep a bit, it was good enough to consider staring the bike.

My info was that the bike hadn't been started since the 1980's, I could be wrong about that. Anyway with the ignition off the engine turned over on the kickstart smoothly. I cleaned the points and sprayed a fairly heavy mix of fuel and oil into the intake ports and turned the engine over a few more times. These engines have roller bearings and as long as they haven't rusted they should be alright with a bit of oil. The engine felt smooth and the compression was ok. I put in a new battery, then put a little premix in the tank. I choked the carbs, turned the ignition on and gave it a kick.

Wonderful !!! It started first kick. It idled for about five seconds then stopped. I tried the kickstart it was locked solid. I didn't try any anything else. I'll pull the engine out and see whats happened. Could be anything. I doubt if it's a catastrophic failure. The engine was only idling at about 800 rpm when it stopped. We were getting ready to move at the time so I haven't touched the bike till now.

One thing I did do was to set up an ebay watch for a bowl for the carby. I also contacted Mikuni and many other retailers and specialists to get a bowl. No luck at all, seems the 28mm Mikunis on that are not even known to exist nowadays. Then I came across a set of three from the same model. They were being sold by a wrecker in Ireland. I only needed the bowl but he wouldn't break up the set, so I unwillingly bought all three for almost $150.00. They arrived a few weeks ago and so I began to pull them apart. I thought I would keep the bowl and restore the rest and on sell them again.

I don't know if that is possible. Externally they didn't look too bad, when I began to dismantle them.....yuck and double yuck. The slides were stuck, which I expected. When I removed the bowls, disaster. They were full of a white crystalline substance. I have seen similar stuff on the inside of carbys before but nothing like this. They are almost full of this crap. I don't know if it's a by product of the breakdown of the aluminium or something else, but it's extremely hard to remove. See Below.

It's amazing the entire bowl is just full of the stuff. It had formed around the float and was extremely difficult to remove without damaging the float. Nothing seems to dissolve it. I'll keep looking for a solvent but if I can't find one it's a matter of a lot of time and patience to remove it. I hope the bowl hasn't got a hole in it.

Here a a couple more photos of the stuff.




I'm going to pull the engine out in the next week or so to see what has stopped inside it. I'll post the process.