More YZA for sale

[Slakewell]

Nice looking bike and the price isn't silly

http://www.vintagemx.us/cgi-bin/largephoto.cgi?C=xfa1uu8jNe9qVa9e

[firko]

There's a bit of work to make it legal for our pre '75 rules. The '79 top end would have to go which would mean the rod would too.....therefore an engine rebuild before you start. Not sure about that swingarm too.

[Davey Crocket]

The top end would be OK, they just use a spacer under the barrel so you can use a later rod and piston. This also necesitates getting a sleeve made up. Very expensive engine to get parts for.... they where originally chrome bore and genuine pistons, rings and rods are hard to get. This makes it cheap and easy to rebuild later on. I think the swingarm would have to go to the bin though as nobody made aftermarket arms for them back in the day.. The price of the bike is OK.....room for movement there.

[firko]

The top end would be OK

With respect John, I very much doubt that. If, like the seller says it's from a '79 model there's no way it'd pass scrutineering as the barrel on the engine is regarded as a major component so being 4 years past the cut off date is stretching it more than a bit.
I agree with the swingarm though. If indeed it is a Pro-Fab it wasn't made for this model or for any Yamaha. That's fine  if the bike it was made for is 1: a pre '75 bike and 2: the swingarm is an actual period piece or a correct modern replica but I've got my doubts. I suspect it's made by Karl Landrus and has no historic precedent. I'd be happy to see a period photo of a YZ or any bike with a similar swingarm. Karl is a major fabrication talent and his generic swingarm may be legal in the USA but they're ilegal by our rules*.

*Karls replica swingarms are good tackle and absolutely legal..it's just his generic swingarm that bothers me.

[RED ALERT]

The way I read the ad, is that the bike runs a '79 piston with the spacer under the YZA barrel for clearance.
Could be wrong but thats what it sounds and looks like. A '79 head would have radial fins I think.

[Slakewell]

If it ran the 79 Barrel it wouldn't need the spacer? If it's just a 79 rod and piston it's a tuff call to say it's not with in the sprit of the sport.

[Davey Crocket]

He is using a YZA barrel and head.....just modified with a sleeve so it can be rebored and the spacer is to suit the new rod/ piston combo....there are heaps of YZA/B,s (250 and 360) running that combo. If you look at Adam Scard's 360A that he sold last year? that was featured on the cover of VMX magazine it has the spacer. It sold for $14.000. I think the piston and rod used is irrelivant as geniune stuff is like hens teeth and most collectors/restorers/racers that have geniune stuff will not part with it. You have to remember these bikes where made in very limited numbers and outdated very quickly. Parts availability was always in short supply. Cool bikes though.....one day I'll get a 360 to go with my 125 and 250.

[paul]

He is using a YZA barrel and head.....just modified with a sleeve so it can be rebored and the spacer is to suit the new rod/ piston combo....there are heaps of YZA/B,s (250 and 360) running that combo. If you look at Adam Scard's 360A that he sold last year? that was featured on the cover of VMX magazine it has the spacer. It sold for $14.000. I think the piston and rod used is irrelivant as geniune stuff is like hens teeth and most collectors/restorers/racers that have geniune stuff will not part with it. You have to remember these bikes where made in very limited numbers and outdated very quickly. Parts availability was always in short supply. Cool bikes though.....one day I'll get a 360 to go with my 125 and 250.

so you wouldnt,wack a protest  in on that bike ? ,if he beat you for a place  in the nat for instance 

[mx250]

He is using a YZA barrel and head.....just modified with a sleeve so it can be rebored and the spacer is to suit the new rod/ piston combo....there are heaps of YZA/B,s (250 and 360) running that combo. If you look at Adam Scard's 360A that he sold last year? that was featured on the cover of VMX magazine it has the spacer. It sold for $14.000. I think the piston and rod used is irrelivant as geniune stuff is like hens teeth and most collectors/restorers/racers that have geniune stuff will not part with it. You have to remember these bikes where made in very limited numbers and outdated very quickly. Parts availability was always in short supply. Cool bikes though.....one day I'll get a 360 to go with my 125 and 250.

so you wouldnt,wack a protest  in on that bike ? ,if he beat you for a place  in the nat for instance 

If you protested that bike it would only be cause you could - any mods would not giving a winning edge .

[paul]

id like to see that engine on a dyno compared with a un modifided one.i take it i has a different stroke ie haveing the spacer etc

[Davey Crocket]

Engine displacement stays at 250cc, it's all about matching the right components together, the bore stays the same size, you have to have the spacer because the rods a different length and thats what the spacer is for to bring it back to the right stroke. It's all about keeping the engine going so theres another bike on the track. There are heeps of engines running similar set ups out there....where do you get KX pistons?....PE400 pistons and gaskets have only just become available from old mate in the states that is on the forum, and I'm sure alot of the Euro bikes have god knows what inside the cylinder, like I said, it's perfectly legal and in a lot of situations it's the only option. I'm sure Lozza could explain it better.

[JohnnyO]

The stroke doesn't change, the spacer is to raise the cylinder to the correct height because of the longer rod. Should be perfectly legal and there is no performance advantage.

[firko]

The seller wrote:

The motor has the spacer under the Cly. So you can use a 79 YZ Top End..(Easy to find parts

which to me could either mean that it has the F model barrel or that you could fit it if you wanted. Now I've thought about it a bit more I realise that the '79 model barrel wouldn't fit without a fair bit of surgery so I think he's used the late rod, piston and skirt. The 214 to 311 rod and appropriate piston change isn't an issue, I've done it myself in the past. The issue now would be in using the F model sleeve and porting the original YZ barrel to suit which would in effect give you '79 model porting. If those porting specs can be achieved by conventionally porting the YZA barrel then I reckon he's legal but if there is a major re design needed to bring the YZA up to F specs I have a real problem with it. Not being familiar with the YZ250 F I'll leave that dilemma to my more learned Yamaha aficionados. I'm curious to know whether the F model porting specs are achievable in an A model barrel.

Id like to see that engine on a dyno compared with a un modifided one.i take it i has a different stroke ie haveing the spacer etc

As Johnny O said, changing the rod length has nothing to do with changing the stroke. The stroke is changed by altering the distance between the crank centre line and the crank pin centre line. It's a common misconception that changing the rod length changes the stroke.

Looking at the engine in the bike it's fairly clear that he's using the original YZA barrel so if the liner change is kosher, I reckon the bikes kosher*. The wording of his ad could be taken both ways.
*I still have issues with the swingarm though.

[Davey Crocket]

You cannot buy a "ready made" sleeve for these engines...you have to get it machined up....George Mckenzie is doing a 250B barrel for me at the moment. The std porting in these barrels is pretty good according to George so he is leaving it stock...I cant remember what piston and rod he chose  but it's ended up working without the spacer...piston pin height and rod lenght cancelled each other out but now I have an engine that has 4 rebores in it....should outlast my VMX racing days.  The swingarm is definately not period and would need replacing. Still a cheap YZ250A to get into.

[firko]

If indeed it is a Pro-Fab it wasn't made for this model or for any Yamaha. That's fine  if the bike it was made for is 1: a pre '75 bike and 2: the swingarm is an actual period piece or a correct modern replica but I've got my doubts. I suspect it's made by Karl Landrus and has no historic precedent. I'd be happy to see a period photo of a YZ or any bike with a similar swingarm. Karl is a major fabrication talent and his generic swingarm may be legal in the USA but they're ilegal by our rules*.

I received the following email this morning from a guy who is pretty knowledgeable in these matters which disputes my opinion on the legality of the Pro-Fab swingarm on that YZ A. If my friends conversation with Tom White confirms the availability of Pro-Fab alloy swingarms for the YZ A in 1974, I believe that the swingarm to be legal. The combined knowledge of the forum membership never fails to impress me.
First off though, the Profab rectangular swingarm on the YZ-A is 100% 
legal.  Discussions I have already had with Tom White, for one, prove 
to me that Profab, for one, made and sold rectangular (some in 
aluminium) swingarms in 1974.  There's no ifs or maybes.  There's 
lots more examples from other riders/manufacturers.

The std porting in these barrels is pretty good according to George so he is leaving it stock

That's cool John but how close is the '79 porting to the '74? Are there any extra ports and do the ports need to be repositioned in the A barrel? Is there any welding required?