Sick GS1000G motor explained

[Anonymous]

Well, I finally took the thing apart. I didn't like what I saw inside.

This motor had busted a piston some time ago with another owner. Then a friend had bought it in pieces. He got sick of fixing it himself so he took it to a motorbike shop to finish it. This is who I bought it from.

When I lifted the head and barrels I found that somebody had put the wrong piston in to replace the junked one. This piston is a Suzuki part but it has no lower land for the oil rings above the wrist pin. It must be designed for different oil rings altogether.

The effect of the piston was that the oil rings have carved out horizontal damage on each side of the barrel about a half inch below the head. The damage is probably 2 mm deep, 5 to 10 mm high, and extends for about two inches wide.

There is also severe vertical scoring on both sides of the barrel where the wrist pin circlip came adrift from one side and damaged that side, then it seems to have gone through the wrist pin to the other side and damaged that as well. In each side bits of it have caught in the unsupported oil rings.

The result is a barrel too badly damaged to repair and a damaged piston that should not even have been in the motor. The bike has also been running way too rich and the carbon build-up was very heavy in all chambers. And the head has some valve guide wear that needs work. And all the rings in the other cylinders are down below their limit as well.

I visited the mechanic who did the work this week to ask what he had done to the bike, but I came away very uninspired and not wanting to return. However, I am in touch with another mechanic who does top class work and will get him to do any machining that I need.

And today I lined up a guy who has a spare GS1000G motor sitting in his shed (with a hole in one piston :?), and another guy who has a spare head that he thinks is a E or S model (a bit more grunt in the cams).

So in a week or so I guess I can put together enough bits to be back on the road with a properly done repair. Then I get the new mechanic to sort out the tuning and the bike will be very happy with me.

Kim

[Anonymous]

Bad luck fella.

I think E and G model cams are the same. S model cams are peakier, you may prefer not to use them. I am converting my S to E spec cams. The S cams don't give enough increase in top end for the amount of midrange they take away.

[saaz]

Its a wonder the thing ran at all!!! Imagine what it will be like running properly.........

[SqDancerLynn1]

could it have been a two stroke piston???

[mcycle-nut]

YIKES! It's a wonder the guy knew which end of the wrench to use! 8O

[Anonymous]

Sick GS1000 motor revisited

Hi Folks,

Well, tonight I got the GS1000G running again. It's taken several days and about 30 hours work, well, lots of sitting and thinking between the actual doing. :-)

I've replaced the barrels, one piston, and one valve. The bits I got from a guy with a damaged GS1000G motor sitting in his shed for some years, waiting for him to do it up. However, his GS850G is going so well (400,000 kms with a rebuild 25,00kms ago) that he sees no need to put in the 1000 motor. So he just gave me his 1000 motor to use whatever I needed and we'll work out a price for the bits I take.

Here's what I now think happened to mine.

That unusual piston is the shape it is because it melted. It used to have lower land under the oil rings, but it just melted out and left the rings floating in mid air. It also melted the circlip slot on one side and the alloy closed up around the clip. It's now embedded into the metal of the piston. And on the other side the circlip slot melted and the clip went astray and foulded up the barrels. The "semi-floating" piston rings did the rest of the damage.

There is also more damage to the cylinder wall than I noticed at first. I described the damage to the top area of the wall, there is similar damage to the bottom of the cylinder, once again on each side of the piston.

When I fitted a new piston to the conrod I found the gudgeon pin very tight. When fitted they should "grip" the piston and rock easily in the conrod. This one gripped the piston and double-gripped the conrod. It was too tight to rock back and forth like it will in operation. This conrod shows damage to its top from the original piston collapse. I suspect that it was slightly damaged in that original event and so gripped the pin to tightly opn the repaced piston, so the pin overheated, and the heat transferred to the sides of the piston, which is where the melted areas are.

When I found the pin was too tight as I was putting in the new piston I took the conrod bearing out a little until the pin had normal movement. It now spins easily and I hope the hot-melt will not happen again.

I also did a leak test on the valves. Having the head off meant that I could service those that were leaking a bit and replace on that had got a bit pounded with a valve from the other motor. It's good to have a lot of spares. :-)

I will have to get some pics of the melted piston and the damage it did to the cylinder for you. 8O

In all of this I have also come across a bike mechanic who does marvellous work and I am going to drop the bike in to him to give it a going over while I'm on holidays in the next few weeks to tune it up, sync carbs, jet for my filters/4into1 pipes etc. Considering that the rings are at their lower limit and valve guide seals are starting to leak I will give the rest of that work to him next winter.

It's good to hear the old beast start up again. It will be better when I get it on the road and am feeling confident that it isn't going to fall apart again.

Kim

[saaz]

It could be hat it will go for ages as it is...good luck!!!