1970 Suzuki T500: shattered piston skirt!!!

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1970 Suzuki T500: shattered piston skirt!!!

Postby ericsattic » Sun Apr 29, 2012 2:42 pm

I was riding my 1970 T500 and my left cylinder went dead on me, no noises or anything it just died, luckily I was close to home and managed to limp back home on one cylinder. I immediately pulled the plug and noticed the electrode had just about melted together because it had a small piece of metal stuck in between the electrodes. No hole in the piston, no scorching, burns, or other visible damage to top of piston, cylinder walls as smooth as glass, etc... But I also found a couple of tiny pieces of metal inside the exhaust port... I pulled the jug and low and behold the skirt on the piston facing the exhaust port has been completely shattered!!! The top of the piston looks fine and there is no damage to the rings, etc... Plenty of two-stroke oil seems to be getting to the cylinder, crank, etc... It seems "most" of the pieces of the shattered skirt ended up in the exhaust pipe; I found them there after I removed the pipe and baffle, then lots of tiny pieces fell out. I believe the piston is a genuine Suzuki piston; top of the piston has an "L" on it with an arrow, which is correctly facing the exhaust port. The piston is also correct for the 1970 T500 because the skirts are solid (pistons for the 1968 Cobra are different and have a hole in the skirt). I have done a little research and unfortunately it seems that shattered piston skirts like this are not all that uncommon on the T500. I am just getting the thread started here so I have some questions:

*what are some causes for this type of piston failure - too lean fuel mixture due to carb settings (jets are stock); pre-ignition due to incorrect timing; crappy piston design, etc...?

* just prior to this the plug had completely fouled on a prior ride. A week or so later I changed the plu with a new one, which was in use on this fateful excursion.

* Plugs in the bike were a B7HS, though many people use them I now realize those are not truly correct, they may be too hot, I purchased some B77HC plugs and will use those in the future on this 70 T500 and already put them in my 68 Cobra.

*with regard to fuel mixture I have a habit of putting the 91 octane lead-free gas in my bikes (no more) and in the fall I had loaded this bike's fuel up and ran it shortly with what I now think is too much stabil fuel stabilizer for fuels with ethanol, along with a strong dose of sea foam for winter storage! Even if its not the problem, I now use the lower-octane fuel AND the correct mixture of fuel stabilizer.

*it seems "most" of the piston debris ended up in my exhuast pipe; but what about potential debris i the crankcase? This is an "early" model T500 and has crankcase drain plug holes; could I pour say diesel fuel into the crankcase and attempt to wash out smaller pieces? Does the case have to be split?

*Should I replace the piston with a genuine Suzuki piston, or go with say a wiseco? If I go with something else, it's obvious I should replace BOTH pistons.

* I managed to remove the exterior piston pin "circlip" that holds the piston in place with the piston pin on the connecting rod. However, the interior circlip is very hard to get to. Is removing the other jug the only way to get more space to get to the other circlip, or does someone have any special tricks they can share?

Obviously more to follow, thanks to all in advance for reading and offering some potential advice, Eric
1968 Suzuki T500 Cobra
1970 Suzuki T500 Mark III
1970 Kawasaki 500 Mach III - H1
1970 Yamaha R5
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Re: 1970 Suzuki T500: shattered piston skirt!!!

Postby muzza » Fri May 11, 2012 10:28 pm

That is bad luck, thanks for your detailed post. I am travelling so can't write much, hopefully someone more mechanically inclined will.
Question, how worn was the piston or the liner. Excessive wear could lead to skirt collapse if there is too much clearance.
In years of riding and racing i have never suffered a skirt collapse so would not think it commonplace.
As to piston i would use a gt750 piston and not a wiseco.
You may be lucky re crank but can never be sure without taking it down and cleaning it thoroughly.
I agree with you over colder plugs and i always used a degree colder when touring. I also raised the slide a notch to run richer to cool the motor

cheers


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Re: 1970 Suzuki T500: shattered piston skirt!!!

Postby dinoGT » Wed May 16, 2012 4:05 pm

I know what's happen to you... too olds pistons (both), I had the same thing 4 YA... cylinder and con rod out... the piston pin was going threw the cylindre... like a chain saw.
You must rebore the cylinders and news pistons kits, suzuki or Wiseco
You must open all your motor because you have piston alloy into... you MUST wash the head conrod...
Look seriously at the feet con rod
Can't answer you about gazoline because I am French but do not use etanol, it is dangerous for your motor.
B7 is not good, for road B8 or B9 when hot (over 25°C)
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Re: 1970 Suzuki T500: shattered piston skirt!!!

Postby Zook-e » Thu May 17, 2012 3:03 am

I had been in a long back and forth messaging with him and it was a low mileage motor. The cause of the shattered piston was the previous owner had used a 68 windowed piston in one cylinder and stock one in the other. Evidently the previous owner had bought it on e-bay listing it as a fit for all T500 engines.
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Re: 1970 Suzuki T500: shattered piston skirt!!!

Postby Batterstyle » Sun May 27, 2012 9:46 am

Sorry to hear about your bike dropping it's skirt! I agree with Muzza, I have never heard of this happening with the T or GT500. Mixture or plug heat range should not at all cause this. For mine there could be only 1 cause. Just plain and simple metal fatigue. Given that the pieces are small this is hightly likely. If you think you can flush the pieces out through the drain holes I would go for it. remaining pieces will end up in the exhaust pipe anyway. The alloy will not harm little or big end bearings etc as it is just simpy too soft. However if you have any doubts about the crank/seals/gearbox maybe you could consider stipping it apart. If not make sure the bore is ok. Replace the piston and little end bearing. Re getting the circlip out that is easy. Just pull the other barrel off. Hone both barrels.Put new rings in from the ring set. If the other piston shows scuff marks replace it as well.
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Re: 1970 Suzuki T500: shattered piston skirt!!!

Postby Bikegeezer » Mon May 28, 2012 5:17 am

Zook-e wrote:I had been in a long back and forth messaging with him and it was a low mileage motor. The cause of the shattered piston was the previous owner had used a 68 windowed piston in one cylinder and stock one in the other. Evidently the previous owner had bought it on e-bay listing it as a fit for all T500 engines.
I suggested to him that was exactly the cause when he posted this issue on the VJMOG forum, but he swore the machine didn't have windowed pistons installed. I guess he assumed it didn't, because the remaining piston was proper. How did you get this info about the PO's debauchery?

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Re: 1970 Suzuki T500: shattered piston skirt!!!

Postby Zook-e » Wed May 30, 2012 1:45 am

I had a very long back and forth pm session with Eric. After many questions I found out what had been done to the bike by the PO. With such low mileage it is hard to imagine that much was done. Only thing I can determine is the PO kept throwing parts at it not knowing how to bring a barn find back to life. Too many times windowed pistons for the T500 are listed on e-bay as 68-77 pistons. One really needs to know there stuff with vintage bikes.
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Re: 1970 Suzuki T500: shattered piston skirt!!!

Postby ericsattic » Thu May 31, 2012 1:47 am

Thanks to all here for the posts and PMs, especially old Z00k from right here in Virginia. And sorry about the confusion but the bike DID NOT have a windowed piston in the left cylinder - both pistons were non-windowed and correct for the bike. Anyway, my story continues below complete with a link to photos. I pulled the heads, cylinders, and pistons off and I finally learned why the two stroke addicts are always talking about crankshafts. I believe the reason my piston skirt shattered is because of a combination of excessive piston / cylinder clearance AND a shot crankshaft. It seems to me the bearings on the big end of the connecting rod / crank pin bearings are excessively worn. So, I am going to have the crank rebuilt, cylinders bored, buy new pistons, rings, pins, etc... Probably just a six-pack's worth of repairs for most of you, but for me it's a 1/2 keg job (just wish some of you lived closer to help me drink it - and pitch in on the work)!

I put together a bunch of photos in a picassa web album that can be accessed in the link below. Click on the link, click on the small thumbnail photo in the upper left corner of the page to enlarge the photos and get the slide show started, then just click the grey arrows on either side of the photos to toggle through it all. Read the narrative too, some hidden topics for another post. Looking forward to some comments. PS - from now on when I purchase a "running" bike I am going to pull the heads and cylinders as soon as I can to inspect the pistons and connecting rods for wear before I do too much riding! Regards, Eric

https://picasaweb.google.com/1174857257 ... directlink
1968 Suzuki T500 Cobra
1970 Suzuki T500 Mark III
1970 Kawasaki 500 Mach III - H1
1970 Yamaha R5
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Re: 1970 Suzuki T500: shattered piston skirt!!!

Postby dinoGT » Thu May 31, 2012 9:01 pm

Nice pics
It is not a big failure but you must be ok when you say too much play in the cranckshaft (i think also too much cyl/pist play).
In some day I will put one photo of my piston failure... the failure top of the top ...
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Re: 1970 Suzuki T500: shattered piston skirt!!!

Postby Batterstyle » Mon Jun 11, 2012 11:45 am

Great pics. Hmmm...For mine I don't see how a worn big end can cause this. Also if it was worn out it would have made a knocking noise. There would also have been indents on the piston crown from the shrapmetal due to the bearing failure. This metal would have been transferred by the ports to the top of the piston. Big end failures on T500 engines are very rare. Did you use a micromter to measure the bore? Vernier calipers are no way to measure this. Get an automotive engineering place to look at your bores. They may just need a hone. If you do pull the crank out make sure newe seals are put in.

PS. I am jealous of your bike collection!
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