someone who knows about a 86 rod in a 87 motor

[LT250Racer609]

ok well The cnnecting rod bearings just went in my crank so time to split the cases. However, its a 87 motor. Now if i were to buy a 86 rod, i will obv. need the spacer plate which i have one laying around. But what piston do I need? a cr250 piston?? or a 86 250R piston. The cylinder is only a 250 GT thunder stage 3 port and polish....i might do this with my backup motor if it makes decent low,mid range on my 310 motor.

[iamjasyn]

86 cranks are about 5mm shorter than 87-89. You don't need a spacer plate for a shorter rod. You just need an 86 250r piston.

[atvmxr]

you run 86 piston with 86 crank or 87+ piston with 87 crank = no spacer plate

run 86 piston with 87+ crank then you need a spacer plate

[LT250Racer609]

and will a 87 crank with a 86 piston and the spacer plate be a plus?? or just keep it 87 crank,87 piston?

[matt250r21]

The whole thing with running an 86 or 84-96 CR piston in a long rod motor is this:

1) The long rod gives a less extreme angle on the piston, so piston ware is lower.
2) Long rods give a little more tourque, 86 or CR rods give a little quicker revs.
3) 86 or CR pistons are a better design because there is less blow by were the wrist pin goes thru the piston. 87-89 pistons are machined in that area and allow blow by.
4) 86 and CR piston give you larger bore options.
5) The 87-89 long rod with 86 or CR piston gives you more case volume which also helps lowend.

Some people love the full 86 setup, some the long rod with 86 or CR piston and spacer. All depends on what you want. I would say try them both and see what suits you.

[LT250Racer609]

what i will prolly do then is just keep my 310 with the standard rod (87) and set my other 87 motor up with the standard rod also but with a 86 style piston.