Posted June 01, 2008 - 12:44 PM
Posted June 01, 2008 - 05:53 PM
i currently have a wr400 and read somewhere that itstalling the crankshaft from a 426 was an upgrade is this true cheers ben
The crank from a 426 will drop right into a 400. BUT (you knew that was coming), it's not a free ride and you will have to account for the following:
1. The small end on the 426 rod is 19 mm vice 18 mm for the 400 making it stronger. Therefore, the 400 piston wrist pin will be too small and you can't use your current piston
2. The gear on the right side of the crank that drives the counter-balancer mechanism is held in place with a Woodruff key on the 400 crank, whereas the 426 crank is splined so you can't use that gear.
Your options, then, are:
1. Buy a 426 cylinder (which will drop right in) and piston and you are now up to 426 cc. The 400 head works just fine with the 426 cylinder (with the proper gasket).
2. Bore out your current cylinder to use a 95 mm piston to give you 426 cc, or better yet go larger with the 97 mm piston to give you 444 cc. There's enough material in a 400 cylinder to bore it out to 97 mm. Both the 95 mm and 97 mm pistons use 19 mm wrist pins so they will fit the small end of the con rod just fine. Also, the 400 head with the proper gasket will bolt up to either the 95 mm or 97 mm configuration without any issues.
3. Buy the splined balancer drive gear for the new crank.
All of the above assumes you will be using a 426 crank/rod. The other option is to rebuild the 400 crank with a 426 rod which will allow you to retain the current balancer drive gear. All of the above will still apply.
I have two 400s, both of which have had the stock cranks rebuilt with the 426 rod. One cylinder was bored out to 95 mm and the other to 97 mm. I'm still running the stock Woodruff keyed balancer drive gears.
Hope this helps.