Vintage Yamaha
- Thread starter Rev Brown
- Start date
Ted Hamilton
Helmet Painter / Racer
You may have better heat transfer through the cases.... I don't think that the dome shape or size are different, so if it's built to WKA or IKF specs, I'd expect similar performance. If it's stock, probably not, except against other stock engines. Since there seems to be little rules enforcement or tech at these events anyhow, I'd throw it on and go run....odds are someone will be at the same speed due to engine similarity or lack of driver skill... (ie. they're slower than their motor theoretically is...) 
Go have fun... or get a "new" style -- they're going for pennies on the original dollar these days, at around $350 for good blueprinted ones that are ready to run...
Go have fun... or get a "new" style -- they're going for pennies on the original dollar these days, at around $350 for good blueprinted ones that are ready to run...I'm a LONG WAYS from an expert, but one thing that has changed from '80's are until now is back then the ports had to be "as cast", but in recent years they can be polished.
I believe the more modern cylinders have bigger transfer ports. I think the port timing is the same, but the opening of the transfers up the sides of the cylinders are bigger.
Mechanically, the connecting rod and bearings have been improved through the years.
This is as much as I know, and I'm not really 100% sure about that....
I believe the more modern cylinders have bigger transfer ports. I think the port timing is the same, but the opening of the transfers up the sides of the cylinders are bigger.
Mechanically, the connecting rod and bearings have been improved through the years.
This is as much as I know, and I'm not really 100% sure about that....
Rev Brown
Member
Thank You
Keep in mind there’s two Yamaha classes offered in VKA. Stock appearing and limited. Stock appearing is exactly that. It needs to look stock from the outside including the carb but internal modifications are allowed as long as the stock bore and stroke are maintained. I have both old and new style engines in stock appearing form and both are equally competitive.
The limited class is a spec class. Engines need to be wka legal and use the S-ry pipe. Again both old and new style engines are competitive. Tech is performed at all the Northeast VKA events. Yamaha class are the biggest at VKA events. Their will be someone there to run with regardless of your speed.
The limited class is a spec class. Engines need to be wka legal and use the S-ry pipe. Again both old and new style engines are competitive. Tech is performed at all the Northeast VKA events. Yamaha class are the biggest at VKA events. Their will be someone there to run with regardless of your speed.
Rev Brown
Member
Hello,
And thanks for the reply.
I am well aware of the rules and the classes in VKA.
I will be running the over 60 Yamaha class, vintage tires etc.
Im over 70 but still very competitive.... I want that $5 plastic trophy !!
That being said I am looking for a BPrinted Yamaha new style.... whats out there?
And thanks for the reply.
I am well aware of the rules and the classes in VKA.
I will be running the over 60 Yamaha class, vintage tires etc.
Im over 70 but still very competitive.... I want that $5 plastic trophy !!
That being said I am looking for a BPrinted Yamaha new style.... whats out there?
Pete_Muller
Moderator
Rev Brown,
I wouldn't be concerned with old-gen vs. newer-gen KT100. In theory: old cases and head, newer cylinder might be overall the best choice.
But seriously.... there is SO much more to be gained by getting the setup right (carb tuning, clutch, chassis, etc.), that old vs. new is meaningless.
Good luck in your racing!
Pete
I wouldn't be concerned with old-gen vs. newer-gen KT100. In theory: old cases and head, newer cylinder might be overall the best choice.
But seriously.... there is SO much more to be gained by getting the setup right (carb tuning, clutch, chassis, etc.), that old vs. new is meaningless.
Good luck in your racing!
Pete
Pete_Muller
Moderator
Rev Brown,
A bit more info for you that might be of use:
- Very old con rods are best, (provided they are not worn to excess or thrashed in some other way). The "X" rod (that's the letter on the side put in during the forging process) was always my preference, though I haven't seen one in years, and don't have any in my possession any more. The material used in those old rods was simply better/stronger. The large end of the rod did not go "out of round" when running excessive revs, like the newer rods did. Shoot for .0013"-0015" clearance on the big end rod bearing, and .0008" to .0010" on the small end. Put a micrometer to the crankpin, and then mic the rollers in the big-end caged bearing. Add 2 roller diameters to the pin diameter, and zero your dial bore gauge at that size. Then you can measure the big-end bearing clearance. Hone if necessary (on a real Sunnen honing machine -- do NOT attempt to enlarge either end of the rod without the correct equipment).
- Jim46 eludes to this, but the actual proper explanation is to go from a "top-located" con-rod to a "bottom-located" con-rod. This requires different bearing on BOTH ends, and then of course the correct thrust washers for the bottom end. In my experience, .012"-.015" is a really good target for side-play on the bottom-located setup. Note that you *must* use a wider caged bearing in the upper/small end of the rod. DO NOT locate the rod at both ends!
Pete
A bit more info for you that might be of use:
- Very old con rods are best, (provided they are not worn to excess or thrashed in some other way). The "X" rod (that's the letter on the side put in during the forging process) was always my preference, though I haven't seen one in years, and don't have any in my possession any more. The material used in those old rods was simply better/stronger. The large end of the rod did not go "out of round" when running excessive revs, like the newer rods did. Shoot for .0013"-0015" clearance on the big end rod bearing, and .0008" to .0010" on the small end. Put a micrometer to the crankpin, and then mic the rollers in the big-end caged bearing. Add 2 roller diameters to the pin diameter, and zero your dial bore gauge at that size. Then you can measure the big-end bearing clearance. Hone if necessary (on a real Sunnen honing machine -- do NOT attempt to enlarge either end of the rod without the correct equipment).
- Jim46 eludes to this, but the actual proper explanation is to go from a "top-located" con-rod to a "bottom-located" con-rod. This requires different bearing on BOTH ends, and then of course the correct thrust washers for the bottom end. In my experience, .012"-.015" is a really good target for side-play on the bottom-located setup. Note that you *must* use a wider caged bearing in the upper/small end of the rod. DO NOT locate the rod at both ends!
Pete