85/86 250r crank/rod question.

[Preddy05]

I was going to put my motor together on my R this weekend but the rod has play up and down so I'm going to replace it. But i have a couple questions before i do.

1. What gains are there to running a 87-89 crank/rod setup?
2. I already have 85/86 piston kit so if i go with the longer rod i would have to run a spacer plate?

Pros and cons would great to know.. or should i just stick with the short rod?

[DeePa]

using the long rod 89 trx rod and the short rod 85-86 piston and a 4.5 mm spacer plate will give you more torque down low. I just did the swap over the winter and i like it. You will have to either open up the bolt hole for the top motor mount or just decide not to use it.

Extended studs are available. I have the part numer at home. Extended dowels are no longer available from honda but maybe yamahondaman here on the boards can hook you up with a set for a price.

A new crank is about 400 bucks from service honda. Id go that route. Throw a new set of cr 500 mains in there too.

Mike

[JohnR.]

IMHO the reliability is improved because with the longer rod you have a less severe rod angle at BDC. A short rod motor will rev up quicker (part of the reason the 302 Fords run so well) but it is at the expense of some reliability. The longer rod gives you more time with the piston dwelling at TDC before it starts moving down again so it results in more overall power.

John

[Preddy05]

Thanks for the info. Im going to order a one of the longer rod cranks. I was looking on the esr website for a spacer plate should i just order the 72-73mm bore one? It will be used on a stock cylinder.. That might sound like a dumb question but it is what it is.