Tear er' down ---- AGAIN.

[Coyote]

I have determined that the problem with my new top end is simply that the ports were not chamferred, Only an edge break was provided. I mean an edge break you could do with a piece of 400 grit paper. I noticed this when assembling, but I figured the hone man knew what he was (wasn't) doing. I refuse to start the bike again because I am certain it's eating itself alive - hence the strong metallic smell and ridiculous noise.
There is no doubt I need to tear it down again and correct this situation. Even though I only ran it for about 15 minutes, I think I have already wasted the rings. It shouldn't be too hard to tear the top end off again if I can get the exhaust out of the way without tearing them off as well. I know in my heart that the motor will only get worse if I continue to run it. If I keep going, I'm going to waste the cylinders as well. I can't afford that. So I need to bite the bullet and tear it down again now.
The books clearly show how those chamfers are supposed to look--dimensions and all. What they don't tell you is there no one on the face of the earth that can do it - per book. I wonder how they did it at the factory?
So forget the impossible dream in the book. What do you guys shoot for and how do you get there?? I do own a counterfeit Dremel and some stones and sanding drum for it. The only hand stone I have is round and extremely fine.

I need a little bitty man with a little bitty die grinder to run in there and do the job

[Craig380]

Last time I did it was by hand using a couple of those mildly abrasive stones for craft / hobby work - one of the cylindrical type was perfect, as it made it really easy to get the angles.

I didn't measure the chamfers, I just went round the ports smoothing and rounding the edges until they felt smooth to the fingertip and didn't snag skin. Took a couple hours to do all 3 jugs.

[pearljam724]

Sorry, to hear about your misfortune. But, as you mentioned. It won't take a lot of time, effort, etc. for you to remove the cylinders and address that. Good detective work on your behalf. But, one thing I question. I remember reading about when your bike originally seized up. From I remember the cylinder walls were scored pretty bad. Were these scores only above and below the ports and I wonder how the ports became jagged all of the sudden ? Perhaps from the cylinders needing rebored long before it happened ? Wise of you to address it now.

[joolstacho]

This can't be rocket-science eh?!
All we're doing here is radiussing the ports so that the rings don't snag on any sharp edges eh?
A cheapo dremel clone and stone (eg chainsaw sharpening stone) should have the ports radiussed smooth in no time eh?
I wouldn't get too hung up on those precise measurements would you? they're only a guide.

[yeadon_m]

Coyote, sympathies and indeed empathy.
My pretty UK GT550B is in bits again for its 3rd rebuild. The first time I had everything done from crank to replated cylinders and new pistons (I sent the motor out and received it back en bloc, cos I'm lazy). The shop was IMO incompetent, fitting aftermarket rods (too long) and I ran the bike 30miles with zero piston to head clearance before they admitted it and sent me base spacers. The bike scored two of its pistons and was noisy. On checking, several ports felt sharp to me, so I sent the top end back. Two new pistons and one newly plated cylinder, sounded better.
150miles in, its just lunched the left side (locked up while riding....even done a 20 foot slide?) and needed a hammer and hardwood to drive the piston out. Wrecked the new crank also. Not a happy bunny. Looking at my piston, it looks (to my inexpert eyes) t be a 'four corners seizure' and if so I read this is too small a clearance.
On both occasions, the shop replated without pistons in hand, which I assumed was crazy yet they told me was fine. I now call BS. Expensive BS, at that. As I have neither the time nor energy to fight the original shop (though I have written to them asking for a contribution of cash), I'm splitting the cases this time and I'm sending pistons with cylinders to a new shop; and the crank is also going to a different, new shop.
If this time it eats itself I will move it on and take the loss.
When it was running, it was lovely. I like the 550 a lot. Just not this one
Cheers,
Mike

[Coyote]

PJ, the bike never did seize. It just had no compression due to a totally fried piston with melted in rings. The PO said he rode it home, but ir ran like crap. The only plan I had was to remove the head and de-carbon. I decided to check the compression just as a 'need to'. That's when I found nearly zero compression on the left. Now I know I had to dig deeper. Both the piston and cylinder were toast.Not just around the ports, but all over. Above and below the ports and 360. Some of the scoring I believe was caused by pieces that broke off the piston above the top ring. Never saw anything like it and no hone job is going to fix it. I toyed with the idea of just repairing the left as the center and right looked fine. Then I decided to get a set of .5 over pistons and do it right. I retrospect, I wish I had just fixed the left. I never did figure out what caused the destruction . My theory is the owner forgot to put oil in the tank and ran it dry before realizing it. It was obviously extremely hot.
So Mike, a 20 foot slide? That must have been a rush! . No biggie though right? Just rebuild the motor and do the laundry

]



A little emery cloth and she'll be as good as new. If you look up junk in the dictonary, it says to 'see this"'.


This is the right side piston. Notice how the rings seem to be breaking down along the upper edge. Looks like it might not have been long before this one lunched as well. I'd give $50 to know what happened to this motor.

[yeadon_m]

Coyote,

Yup, it was, er, interesting.

My left piston looks somewhat similar to yours, but with less widespread scoring, and with 3 deeper melted grooves. No ring pieces lost, no marks on piston crown. Very little bore damage but alloy transfer. I don't know why this happened but speculate inadequate clearance and first hot day ride. I can't find faults with carbs, ignition or lube system and the other two pots are fine.

Cheers,
Mike

[joolstacho]

I'd be interested to hear whether those lunched pistons were aftermarket or genuine Suzi pistons.
I just spent a small fortune on a pair of genuine +0.50mm oversize GT500 Suzuki pistons. I agonised over the decision, because I paid almost 3 times more than you can get aftermarket pistons for. (And I'm on a pretty tight budget!)
My reasoning is, that I'm spending bulk time, shedding plenty of sweat, and maybe a couple of grand foldin' restoring this thing, and I'm damned if I'm going to cut corners on the most important part of a 2-banger motor... the piston/bore quality and accuracy. Save a couple of hundred on pistons? - No, not for me.
I'll probably end up eating my words, but I know that I'm giving the me and bike every chance of good performance and a long life. (Well the bike anyway! )

[GT750Battleship]

Hi,I'm with you,no cutting corners on lots of things during a restoration,The guy who rebuilt my GT750 motor has being doing this a long time,& recommended I use Wiseco pistons & rods,the reason being they are a little more durable than the Suzuki parts & should well & truly outlast me providing air filter & gearbox oil changes are adhered to,I'm a bit "over the top" with maintenance in any case
Cheers,
Roger

[Coyote]

The pistons were original as installed by Suzuki in 1975. My new pistons are also OEM because the .5mm OS aftermarket weren't available until after I bought the ones from Suzuki. Had the .5mm oversize pistons been available, I would have bought them. Now I'm glad I didn't buy the cheapo's as other things I bought from the same aftermarket dealer were a big disappointment. Money wasted.

[ConnerVT]

I'd be interested to hear whether those lunched pistons were aftermarket or genuine Suzi pistons.

You couldn't tell by looking at them?

[Vintageman]

Coyote,

I am not sure I understand. Did you have the cylinders bored over size and installed over size OEM pistons to match and that is what is now noisy? Or did you hone and use same size piston as before?

After the ports are chamfered, I now polish them (chamfer only) with 400 grit. It stops some of those fine scratches on the cylinder walls about the ports caused by the rings knocking off the otherwise rough peaks left by the chamfer tool/stones.

[joolstacho]

I steered clear of Wiseco because of the forged piston / extra clearance needed issue. (Well if I wanted slappy slugs I could have just kept using the old worn Suzi originals!)
Seriously though, does anyone know if any of the repro pistons have the gudgeon pin hole 1mm offset? -My bet is that they don't. Suzuki would have done that for a reason, to minimise piston rock I assume.

[Coyote]

All 3 jugs bored ,5 over and 3 new Suzuki .5 over pistons installed. And yes it's noisy. I believe the excess noise is due to sharp edges on the ports. The port edges were just better than razor sharp. i.e. just hit a quick lick with some emery cloth to remove the razor edge. No chamfers at all.

[Alan H]

I steered clear of Wiseco because of the forged piston / extra clearance needed issue. (Well if I wanted slappy slugs I could have just kept using the old worn Suzi originals!)
Seriously though, does anyone know if any of the repro pistons have the gudgeon pin hole 1mm offset? -My bet is that they don't. Suzuki would have done that for a reason, to minimise piston rock I assume.

An offset gudgeon pin staggers port timing on up and down strokes.