Topic: 400F oil pump rebuild

[eastyork1977]

So someone thought it would be good if I posted a thread showing how to rebuild that pesky 350F / 400F oil pump.

I know that the oil pump on a 400F is actually too small stock and doesn't create enough pressure for the bike and it has issues there. I heard someone has found a way to get a 750 oil pump on a 400F but this thread is just a stock / oem rebuild, plug and play.

So first step, drain all your oil. Best to perform this rebuild with an oil filter and change since you've got to drain the bike anyway.

After you've got the left side cover off, locate the oil pump in front of the shift shaft.
Locate the oil pressure sensor on top the pump.

Carefully remove the tiny hex screw at sensor. Its a number 7. I used a spanner, a JIS bit is very tricky to get up in there.

Remove electrical connection and replace the #7 hex screw back onto sensor to avoid loss.
Locate the wire clamp and pull it open so you can un hook with wires attached to the pump.

Next slacken the oil pump cover hex bolts.

Now pull the hex bolts securing the pump to the inner case and gently pull the pump out straight. You may need to twist it out very slowly.

You'll want to pay close attention to the two large and two small oil passage dowels in the pump when removing. Sometimes one of each or all will stay in the case.
 

[eastyork1977]

Then pull out all the old flat seals that have been in there for 37 years or more. I like to use plastic scrapers and pullers where I can to prevent marring. (I'm only left handed in the pictures cause I'm holding my cam with my right)

Remove the front cover which should already be loosened. There are two seals and one dowel under the pump cover.

[eastyork1977]

Check your oil pump gear clearance using a feeler gage per manual. Be careful with the internals, they can come right out.

Next as the manual states, clean off the faces and internals with gas.

[eastyork1977]

Once you've got all nice and clean and dry its time for the new o rings to go in.

I like to use a good quality vacuum grease in sparing amounts, but I'm sure most lucas greases are good here.

Two seals cover side.

Five seals case side.

I found that one of the listed seals did not fit in the cover. Luckily I had the right one.

I would suggest placing the dowels inside the engine case before replacing the pump. Dowels are in the oil pump in the pics to show that the o rings fit in place.

[eastyork1977]

Next up, make sure that the case is nice and clean for replacement. Dry off before the oil pump goes back on.

Replace the electrical onto the pump sensor before the pump goes back on. Much easier this way.

Gently work the pump back into its original position. Again, twist gently as you go straight into the case. Never force it or go fast.

If you can't get it to sit right, check that the dowels are all the way in the case.
If that still won't work, rotate the gear on the pump just a degree or so, repeat just slightly again if needed.

Once back on, tighten and secure all hex screws and bolts. Torque values are available in the manuals.

Finally secure the oil pump sensor and replace the wire hook around the electrical.

If you've changed the filter now place it back on as well.

Renew with new oil.

Listed o rings below (some of the listed rings in fiche were not correct)

Passage seals:

91302-044-013

91301-MY9-003 (17.5 x 2.5 used)

At case seal:

41123-516-000 (91302-250-010 fit)

At cover:

91309-286-000 (31 x 2.5 fit, listed seemed huge)

Will post a video of the idle later today.

[kajtek]

Thank you for the write up, it is much appreciated. I have ordered o rings as per the details in the how to section, plus another low miles oil pump, so i can choose between the two for the one with the least wear. I will have to see if my o rings fit or not, at least i have the spare pump to trial fit them first.

U mentioned using vacuum grease, is thus to hold the o rings in place or to lubricate the pump as all the oil has been cleaned out?


Ashley

[eastyork1977]

Vacuum grease or paste to seal up nice and tight with the case.

Silicon paste, like sea-divers use, as long as its high temperature is best.
But lucas high quality greases will do too.

I got my hands on some really good quality Audi vacuum paste from a dealership a couple years back but sadly have run out. Really hard to find.

You won't need it to lube up the pump, its just to form a good seal with the engine case side and you don't need a lot. As you mentioned, it will hold the o-rings in place too, which never hurts when you're dealing with fiddly little parts.

[vfourfreak]

Nice tutorial, clear and easy to follow. I will file this link for future reference for when I do get a project underway. Thank you for this.

Two questions if I may :

Do you prime the pump before fitting it ?

Re the CB750 pump in use on 350/400, do you mean the whole pump or some internal pieces like lobe or something else ?

Cheers
Kev

[ttr400]

Nice write up.........however the pump rotors you show are not the main oil pump rotors, these are inside the main pump body.  The rotors shown in your pics is for the secondary pump which feeds the gearbox. i would suggest you do a part 2 of the rebuild.

Yes it is advisable to prime the pump before fitting, fill with oil or petroleum jelly (Vaseline).

CB750 Oil pump parts: The CB750 oil pump has a main set of rotors that feeds the motor (same size as the CB400F) plus a second set of rotors that return the oil back to the oil tank. this is a thicker set of rotors and can be modified to fit the 400F pump, plus with some machining to the pump body. But most 750 pumps i have stripped have been badly worn. thats why i make new rotors for my uprated high volume 400F pump.

I have more but sorry for the thread hijack.

Kevin

[neevo]

Kevin, what tools/machines are required to do the 750 rotor mod? Is it a lathe or mill job?

Also is it something an amateur could do, or best left to the pros?

I have a fully stripped 400F (with TTR rearsets ) that I have bought 3 oil pumps for, but all of them had some form of damage on the lobes (although 1 isn't too bad). Given how much I will have in he motor I'm thinking the 750 mod might be prudent to do.

[eastyork1977]

Thanks for the feedback and no I don't mind the thread jack.

There are some things that omitted or only grazed over.

Main inside lobes were measured and should be checked with a feeler gauge. As mentioned check manual for specifics.

The internals were cleaned inside the pump and inside the cover but I couldn't take pics of that action, so as mentioned, clean with gas.

I did miss posting the prime step so thanks for the catch, I like to prime with oil, but as mentioned by the other members looks like vaseline or grease will do the trick.

[eastyork1977]

tr400 thanks for the heads up on the 750 oil pump mod. probably try that out this summer.
Will be in touch...

This thread was mainly to show the seals needed and tricks to get the pump on and off. I will try and do more posts as I go.
Should be easy enough for anyone to do, but not a beginner job.
You need patience to complete this task for sure.

[vfourfreak]

Should be easy enough for anyone to do, but not a beginner job.
You need patience to complete this task for sure.

And you have helped no end with these posts, again thanks. I only ever drove the wire out of my 400F back in the day, hardly worked on it at all except for changing the cam for a Yosh Road & track, but never delved deeper. I am filing this for when I do.

Kev

[ttr400]

Apologies did not catch that bit.
Neevo, It can be done but some accurate measuring tools would be required. plus the rotor has to be ground on a surface grinder (then hardened again) and the 400f pump has to be milled, i have a jig that i use to hold it in a lathe.

Vaseline is good to pack the pump (especially if it's a while before installation) otherwise engine oil. but not grease, this won't mix with the oil, Vaseline or petroleum jelly will mix. 

Kevin

[eastyork1977]

ttr400, once again on point.
Great point about the vaseline over grease. Did not even think about that but it makes a lot of sense.

I heard that the 400F pumps don't have enough pressure for the bike. Maybe you can tell us what the issues are with the pump as it comes on the bike, seem to have done this a couple times.
Can I send you a pump to mod?