Questions on Winter Engine Rebuild - 400F

I received a 99 400f and partially revived it. it runs ok, but the carb is gunked up and it has a hanging idle. I plan on sending it to Zip-Ty over the winter...

Anyway, here is the issue. Over the past 2 oil changes i have noticed a lot of metal on the oil filter. I also noticed a noise from the engine after the last one. It is not valves - had them checked at yamaha 5 hrs ago. Since there is a lot of metal, I am guessing big rod end bearing based on info found on this site.

So, I guess it is time for a total rebuild. And since the crank is most likely the culprit, I prob should install a 426 crank and top end. Maybe i will go 444 with the $$ i save by doing most of the work myself. So here are some questions i couldn't find answers to in the search forum...

1. will a 400f clutch assembly work with the 426 crank, or should i get a 426 clutch assembly? i read the 426 was different (larger) and therfore stronger.

2. will the stock 426 cyl head bolt to a 400 cyl, or should i just get a 426 cyl off ebay?

3. how difficult is it to replace all the bearings in the cases/entire engine? do i need any special pullers for the bearings?

4. does the 426 cyl head allows the bike to rev faster? my 400f (and others according to my buddy) is very lazy compared to a 426.

any other info, or tips for the rebuild would be appreciated.

The 426 crank is different from the 400 in at least one, possibly two ways:

  • The wrist pin bore in the rod is larger
  • The '01 and later models use a spline driven balancer drive gear, rather than a key driven one. This would require at least the use of the '01 balancer drive gear to make it work.

  1. The 400 clutch should be OK. I'm not certain whether you can upgrade to a 426 clutch
  2. The 462 head will fit, but has no port in the intake for the hot start assembly, as it was included in the carb on that model. If you use the 426 crank, you will need the 426 piston, which means you'll need the 426 cylinder, anyway. The upside is that after that, it will be a 426.
  3. You need a flywheel puller, and some means of extracting one transmission bearing from a blind pocket (like a slide hammer type puller)
  4. Yes, it helps, but that's not all there is to it. The ignition map and cam timing are a bit more aggressive, also.

ok, just to recap a list of the parts i will need in addition to some others i think i need. please comment on stuff i may have missed if you want.

2001 426 crank

2001 426 counterbalancer

oem 426 cylinder core for lukes racing 444 kit

2001 426 cyl head in good shape

all new 400f engine bearings

boysen supercooler water pump setup

426 cdi

hot cams intake cam w/ auto decomp

sounds pricey. still cheaper than a new 450 though, and my suspension was just done for my weight, so i guess that is a plus...

sounds pricey. still cheaper than a new 450 though, and my suspension was just done for my weight, so i guess that is a plus...

Even though it can still be improved (and it can be done very reasonably), the combination of the chassis and the stock suspension on an '06 that you could buy for under $3K is already better than anything you can do to a 400 for $3000. And it's faster than a 426, too. :busted:

so you are saying sell it. i wish you were wrong. no sence in throwing money down a rat hole.

oh well, new plastics and hopefully it sells for $1800 to $1500

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now