Longrod 300r Idea!??

[Daddio]

Over the past four years I've gotten into the performance side of the aircooled 250Rs. When I was growing up my dad had a bodyshop and his hobby was building old hotrods, he's actually still doing it. When he started there were very few high performance parts available so he and his buddies would try different things from other cars to try to make the cars faster or look better. I was strongly influenced by this and now it has carried over into the trikes. This is mainly due to 1upfront getting into dragracing his Rs. As you know the aircooled Rs don't have an abundant supply of high performance parts available for them either. So this old hotrod mentality has helped us overcome some of these obstacles. I have been sitting on some of the ideas that I've had because we haven't had a chance to put them into an engine to see if they would really work.
I'm throwing this one out there because, with all of the current projects going on between us, it could be a few years before we can try it out. Maybe someone else might try this out for us to see how it works.

You can no longer buy new pistons for the Hondaline 300 however the the trx 330 bigbore piston will work. That piston is 4mm shorter on top than the stock 300 piston. When 1up put that piston in his cylinder we were told that the cylinder would need to be machined down 4mm on the bottom so that that the piston would reach the top of the cylinder. That is one way to do it.

http://i39.photobucket.com/albums/e183/lrdunlap/100_0166.jpg

I realized that the reason the piston was shorter is because it was for the longrod trx 250r. What I didn't realize is that the liquid cooled rod could be used on the air cooled crank. When we had the two cranks apart to have the liquid cooled machined to match the aircooled for the 380 bigblock build I measured the two rods and they will interchange. the only thing I'm not 100% sure on is the thrust washer thickness on the big end but that should be simple to figure out. So why not use the longrod with the 330 piston and not modify the cylinder.

What do you guys think? Do you think I'm :crazy: ? :wondering :beer

[Enginerd]

...What I didn't realize is that the liquid cooled rod could be used on the air cooled crank. When we had the two cranks apart to have the liquid cooled machined to match the aircooled for the 380 bigblock build I measured the two rods and they will interchange. the only thing I'm not 100% sure on is the thrust washer thickness on the big end but that should be simple to figure out. So why not use the longrod with the 330 piston and not modify the cylinder.

What do you guys think? Do you think I'm :crazy: ? :wondering :beer

I think this is a great idea!:w00t: I was going to try to do a 380 build similar to yours, but after seeing the post by 1upfront over on .ORG concerning your build, I am not comfortable with boring the cases to allow the 85-86 crank to fit. the case wall between the tranny and crankcase just looks a bit too thin to me.

However, I think using the Oddyssey big bore cylinder and its required machining is still a good way to go, so this post about a long rod with spacer plate makes great sense to me.

Having said that.........I am curious about 250R center to center distances for the various generations of 250R connecting rods.:wondering

Can somebody tell me the Center to Center distances for:

83-84 250R
85-86 250R
Later "Long-Rod" 250R (requires spacer plate)

Maybe Daddio and/or 1upfornt can help as they work at a Honda dealership.

Thanks!

Gary

[Daddio]

Center to center big end to small end is the same on the aircooled and liquid cooled atc's. The width of the big end of the rod is also the same on both as is the pin diameter and bearing. The big end thrust washers on the liquid cooled r are a little thicker than the aircooled machines. This can be solved by using the aircooled thrust washers.

[Billy Golightly]

Mechanically, this should work out great and be a great alternative to modifying the cylinder.

Functionally, with the way the 2 strokes are so damn finicky and how many variables there are, I'm not 100% sure. What your going to run into is modification of not only the ignition timing with the different rod lengths (Different dwell times at TDC will throw the timing curve out of whack from the aircooled curve). Your also going to modifying the port Time/Area of all the ports. The longer rod will take more time to move through the stroke then the shorter rod, so you'll have an increase in the TIME aspect of the port Time/Area equation. I've never done this so I can't say what the exact effect of it is, but it might be necessary to correct the area of the ports to match the increase in time that you'll be having with the longer rod. The guy that ports ya'lls cylinders will more then likely be able to figure all that out for you though, I'm just kind of talking out loud :lol:

[Daddio]

Port timing is affected when you use the 330 piston in the 300 cylinder after machining the bottom of the cylinder also. I don't think using the long rod will change it any more that does. Actually even if that piston had the same deck height as the stock piston it would change the way the engine would run because of the porting on it and cutout on the skirt. The guy that sold us the 330 piston also offered the cylinder machining service and it didn't offer any port work. We had Denny do the machining and portwork because we were planning on using that engine for dragracing only and it was ported accordingly.
1upfront still has a stock 300 kit that he bought from Babbits a few years ago, when you could still get them, that now has about twenty hours on it. We will be using this kit to try this idea out, but we have three other projects in process right now so the 300 longrod will have to wait for a while. I would love to see how it works out. Maybe next year. I love a good challenge.

[Enginerd]

Center to center big end to small end is the same on the aircooled and liquid cooled atc's. The width of the big end of the rod is also the same on both as is the pin diameter and bearing. The big end thrust washers on the liquid cooled r are a little thicker than the aircooled machines. This can be solved by using the aircooled thrust washers.

Daddio,

Do you know how much longer the TRX "long-rod" is than the factory ATC rod...

[Daddio]

I was told 5mm. I don't have one to compare it with yet.

[cr480r]

The long rod will also add crankcase volume

[NOS_350X]

The long rod will also add crankcase volume

Only if you use a spacerplate, not if you relocate the pin on the piston.