Archived Posts

[Admin]

i bought a nos jug for my s 32 that has a huge chamfer. maybe it just looks bigger in that tiny bore

[Admin]

To emphasis the point, this is NOT optical illusion they are BIG champfers but are in every NOS 500 cyl I have seen. I have never seen these in other 2 strokes such as yamahas RDs. So I will try to locate the manuals Allan suggested dont know where but will figure it out cause I am READY to have my freshened up 500 back on the road!!!! and take my other GT apart for rebuild!

Still hoping for more input from some of the raceing guys and the folks in NZ/OZ overseas as well? I am really courious as to why the champfers are so big?? Has to be a reason they were done?

Just a thought, could the port be cooled by the incoming fuel charge enough to cause the edge of the port to interfer MORE with the rings? and need to be champfered that much to insure the ring wont catch?? Its a BIG cyl. for a two stroke? The GT750 is water cooled and may not need the same design?? Guess the book is the way to go. Thanks Dofin

[Admin]

Dofin im curious too as to what you find out cause ill be looking at my 69 Titan eventually and then i'll get to see the large chamfers firsthand.
I need to buy a shop manual for that bike anyway just for the sake of having it for the technical specs, but see what you can dig up in the later Titans and GT500 books.

[Admin]

It seems very strange to me all that chamfering, since 2stokes rely on the ports' pulse effect and that chamfer surely would destroy it
I found some time ago this measurements that worked very well on all my rebuilt engines:



... my two eurocents.

[Admin]

Advant63, I finally checked out your picture and YES that is exactly what I am talking about. Any one interested should save that picture and then make it bigger to see huge bevel at the bottom of the port!! What the heck is that suppose to be for??? Dofin

[Admin]

Is it fair to say that we all understand the reason for port chamfer is to allow the rings to move back smoothly into the ring grooves.

When the rings pass an open port such as the exhaust or transfer the rings bulge slightly into the port and when the piston reaches the top edge, we want to ease the rings back into position gently.

True, the chamfer slightly softens port pulses and timing but the soft landing is more important. One of many compromises in any design.

Why where they so large on a stock T500? I would speculate that it was a safety measure and easy to manufacture that way. If it lost a hp or two, that was less important than not breaking rings.

Race motors are all chamfered because we don't like breaking rings either, but they are more like 1mm to 1.5mm tall.

[Admin]

Dofin,

In case I didn't answer your last question clearly enough, the chamfer on the bottom of the transfers and exhaust is to stop the rings snagging when the piston travels to BDC.

And don't sweat that pulse idea. Look at the roof of almost all exhaust ports and see that they are curved. Really square would create a stronger pulse and a higher peak power over a very narrow range.

The curve allows for less noise, longer ring life and a wider powerband.

That's the same reason that transfers are curved at the corners.

Ports are more about resonance than peaks created when the port cracks open. It's true that the sharp opening of a port creates strong pulses, but they are not always the most useful.

[Admin]

here's a larger fuzzier shot

[Admin]

Now that I see the port clearly, I can honestly say that I've never seen one with that much taper. I think it's extremely excessive, and maybe Suzuki did it so that you didn't need to chamfer the ports after boring to the expected maximum bore. Who knows????




Lane

[Admin]

But at what expense in power on the new engine??? Lane take a look at the second pic on my first post and see what the transfer champfer looks like after the 2nd (1.0) over looks like. It is not completely across the port and is just visible to the right side of the port. Both ports look the same in both cyl.

I inspected a Cyl with 20k miles and you can see where I THINK the rings came in contact with the Champfers just below the transfer port opening, it would be about half way down the champfer. With out the champfer might the rings snag the transfer port?? As TZ375 mentioned in his post. All this is very strange that others have not questioned the champfer and what its for specifically?

We havent heard from the racers on this forum? They have the Cyl. modified, are these large Champfers required on thier engines?? I guess Eric is the one to ask?

I can try to get a picture of the marks for all to see if there is an interest??

[Admin]

I really don't know what effect it will have.


Lane

[Admin]

Dofin,
I think you may be overly concerned. I'm running two cylinders at first oversize that had almost no chamfer remaining after boring. The guys at Wiseco Pistons advised me to use a ball hone to finish some H1 cylinders and chamfer their ports, and it worked great. Sure beat the old bent rat tail file and Dremel tool. So I used one on these Titan cylinders as well. I used a 240 grit ball hone, and the engine runs great. Oil the snot out of the hone, then give it ten full strokes in each direction at around 2 strokes per second and 800 rpm. If you're not happy with it, give it ten more. It won't remove more than .0002" from the bore, and the rings will seat better, too.

http://www.brushresearch.com/brushes.php?c1=1
If you decide to try this, get a BC hone sized 70mm in silicon carbide - 240 grit. Also order a small bottle of their honing oil. If you call the Tech Guys at Brush Research (323-261-2193), they'll walk you through the process. And there's an instructional video you can download from their site at this link. http://www.brushresearch.com/video/EXPO ... 20Flex.wmv

Stu

[Admin]

Yes there is a gloss, a semi gloss and a flat clear, BUT you cant spray the whole badge with it if not the aluminum would then be flat looking too.
I've got a decent example of one of these badges from Suzuki thats not been abused and you can see the flat black paint has been painted on by hand the way its onto the sides of some of the letters.
I'm 99% sure this is the stock flat black paint cause it looks correct and has no layering of being done over.
People think of factories being all mass production now but you have to remember in the 70s a lot of outsourced work was still done by hand.
I'd even go so far as to say the orange metal flake paint on the "GT" side cover emblems was also done by hand too...

Allan,
The tank badges on my GT500 are in excellent original condition, and except for a few small spots of dried white polish, the sides of the letters are completely black. I don't see any evidence that they're hand painted. Is it possible that some of the original paint has worn off the example that you have?

Stu

[Admin]

Dofin,

Are you talking about what appears to be a huge area below the transfer port that is relieved or what's left of the chamfer at the top?

The top edge looks normal but if that large fuzzy pic is what it appears to be, then that is really strange. It looks in that pic to be about 10mm deep and at that size it isn't a taper - it's a relief and I have no idea why it's there. It makes no sense to me.

It would encourage the rings to expand into that area and then into the transfer ports. One could hypothesize that they were there to ease ring expansion into the transfers progressively because Suzuki engineers were concerned about such large ports (for the time). At BDC there would be little or no gas loss through that area so that wouldn't be an issue for them.

Seems to me that if they made them that way without any problems, I wouldn't worry about it and since most bikes don't have them, I wouldn't worry if they are gone. Just make sure there are appropriate chamfers in teh corners and you should be fine.

BTW, I personally wouldn't use a ball hone in any bore I had correctly sized, but I'm probably being too conservative.

[Admin]

DOT 5 fluid may have an adverse effect on the seals.