640 Rear Main Leak After Rebuild

After rebuilding my 640 Ford I got it together enough to let it run. I let it run on and off for 20 minutes at a gentle idle up to 12 hundred RPM s. During this time I adjusted the valves, set the timing and played with the lift.

Today I let it run for another 20 minutes, mostly at 15 hundred RPM s (PTO speed) but a couple of times I let it run at wide open throttle while I adjusted the carb and a couple of times I let it run at enough RPM s to let it move across the shop floor in 1st and reverse.

Everything worked well, the lift goes up and down, the clutch is smooth, the engine purrs like a kitten, no smoke, no blow by.

I shut it down to find a puddle of engine oil the size of a saucer under the tractor. The rear main seal is now leaking bad. I used the Fel-Pro crank shaft seal kit with the 2 piece rubber seal (which I staggered like the instructions said) and the rubber packing material with drive in pins. I siliconed the rubber side packing sections, but tried not to get any on the round seal halves.

Unless someone has a suggestion I guess it is time to tear the tractor back apart and reinstall a seal from beneath the engine. This task I do not look forward to as it appears that I will have to remove the crank from the bottom.


Should I clean and reuse the seal and packing and really silicone the time out of it or get a new seal? I still have the oil absorbing packing and rope seal that came with the engine gasket kit, but I thought those were nothing but trouble. Any suggestions would be appreciated as I read all I could before installing the seal the last time, and now I am really bummed out.

Before you go too far, make absolutely sure it is the rear main seal.

Sometimes it can be oil coming down from above, or a galley plug or the cam plug, can be the pan gasket.

Any investigating you can do before tearing back into it will give you assurance you on the right trail.

Is the seal built into the rear main cap? If so, a common place to leak is pressurized oil from the bearing coming out under the main cap. If that is the case, the seal is not at fault and can be left as is, just seal under the back of the cap with a very thin application of automotive silicone.

Some may have had luck with sealing the rear main without pulling the engine, but I am not one of them. I tried the rubber side seals with drive in pins like you used during your rebuild. I had no luck installing them from underneath with the engine in the tractor. I pulled my engine and with it upside down on an engine stand used the two piece rubber seal on the round journal, and used victor reinz sealant in the side wedge grooves of the rear main cap. Six years and no leaks. The victor reinz is a gray colored sealant, and the tube comes with a long applicator nozzle which helps getting the sealant down into the v grooves in the sides of the rear main cap.

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You will see all I have had to say about'em...

You missed you chance to check for leaks while the engine was out pan off ... Resealing in frame is very doable I would use the victor reinz kit... If its the rear seal go get it its not a hard job at all....

I never stagger the seals just never have and never had an issue.. I used the pin/rubber set one time it won't happen again :wink: I liked to never got it sealed up they are just a P.I.A.
If you use the paper cap side seals put RTV on'em not engine oil as recommended and seal the cap to the block with ultra grey RTV...

The last one I did I did in-frame the engine had just been rebuilt all ford parts I did not see anything wrong with it I went back with the Victor/RTV set all was good no leaks... Its gotta be clean and oil free that RTV is not your every day RTV...

I am at that stage right now, engine is off and mounted on the stand. So I am very interested in
what the procedure is for checking the seals before assembly. Could some one explain it to me?

Steve, I was thinking that the whole time reading this post! Once, I put a rebuilt 390ci into a Ford Galaxie only to have engine oil coming out of the flywheel inspection housing. First thought was rear main seal. Installed new one under the car,not fun. Guess what? Still leaked! Took the car to a buddy's place that had a hoist and pulled the trans. Turns out the shop that had put the rotating assembly together had only put the oil galley plugs in hand tight but with sealer on them.
I called him and he apologized profusely! Only thing he could come up with is the phone rang and when he came back it had slipped his mind to tighten them down.
Moral of this story? Try to be as close to 100 percent certain as you can that that's where the oil is coming from!

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3x what michford and Hobo said. I put a new seal in a 901 5-6 years ago. I used the 2 piece neoprene, seal but I used the rubber and pin side seals. This was with the block upside down on a stand. I pulled the pins back out three times before I was satisfied with them. Never again!! Victor Reinz for me too. So far as upside down, I wouldn't do that. But I certainly would check thoroughly for other possible leaks first. And I would not put silicone any where near that neoprene seal.

Many thanks. That may head off some headaches for me, second time around. The neoprene seals
certainly didn't work so hopefully the VR sealant will.

I have read all the post by HOBO NC and the others. My Son and I installed the seal three times before we were confident it would not leak.

I split the tractor after a close inspection and found it is leaking at the rear main seal. Not at the packing but around the crank shaft.





I plugged the engine openings and hooked the air hose to the dip stick. I could hear the air escaping from around the rear main seal. The curved neoprene section at the top which I thought was unusual. Not the side packing. I verified this with leak finder I used for tires. Not lots of little bubbles but one big gush that would blow all the solution away. I thought some crud may have got trapped in the seal so I blew it out with carb cleaner and compressed air, but that did not help. Actually the carb cleaner ran out the oil pan drain.



I took the oil pan off and found some crud in the bottom. I thought I had cleaned the engine well. Something may have failed. I will tear the rest apart tomorrow.




I still have the rope seals and packing that came with the engine gasket kit. Should I use those or throw them away and just use a Victor-Reinz seal kit this time.

Your call on the rope seals... If you go there I coat the paper sides seals with RTV NO WAY would I depend on the oil to swell them...

Again I do not stagger the replacement seals are the rope either as far as that goes...

https://www.hemmings.com/blog/article/rear-main-seal-repair/

(quoted from post at 17:13:12 05/04/19) I have read all the post by HOBO NC and the others. My Son and I installed the seal three times before we were confident it would not leak.

I split the tractor after a close inspection and found it is leaking at the rear main seal. Not at the packing but around the crank shaft.

I plugged the engine openings and hooked the air hose to the dip stick. I could hear the air escaping from around the rear main seal. The curved neoprene section at the top which I thought was unusual. Not the side packing. I verified this with leak finder I used for tires. Not lots of little bubbles but one big gush that would blow all the solution away. I thought some crud may have got trapped in the seal so I blew it out with carb cleaner and compressed air, but that did not help. Actually the carb cleaner ran out the oil pan drain.

I took the oil pan off and found some crud in the bottom. I thought I had cleaned the engine well. Something may have failed. I will tear the rest apart tomorrow.

I still have the rope seals and packing that came with the engine gasket kit. Should I use those or throw them away and just use a Victor-Reinz seal kit this time.

Click to expand...

The rope seals can work well when installed properly. There is a lot to doing them right. Watch a Youtube video on installing one in a Holden V8. It is very informative.

A few years ago an old experienced mechanic brought his Jubilee to me with a leaking rear seal. The rear seal had been leaking so he replaced it but while he had it apart he threw in new main bearings for good measure. The rear seal still leaked after he put it together. After several attempts with both rope and neoprene seals he couldn t get the leak stopped. Then his shop roof collapsed under a snow load and he decided not to rebuild so he brought it to me. I couldnt get to it right away so my son tackled it. He pulled the engine out, put it on the stand and did a good job replacing the seal. It still leaked so now I tackled it. I put the engine on the stand and while it was upside down I pulled the rear main bearing to have a look and I found the problem. The bearing shell was standard sized and the crank was stamped .010. I put in the right bearings along with a new seal and the leak stopped. I dont know how far you went with your rebuild but while it is on the stand it wont take long to pop a main bearing out to take a look.

I got the tractor apart and the 2 piece neoprene seal and side packing out. Everything looked good with the seal so I don t see why it was leaking. No trash or silicone in the seal and thank goodness the bearings looked great. I was afraid maybe I had spun a bearing.



The crank had some slight pitting on it. It is not as bad as the photo looks. I don t think that was the cause of the leak because it ran for a long time before it leaked, but then who knows. How do I fix the crank pitting while waiting on a Victor seal kit?

(quoted from post at 16:02:59 05/05/19) I got the tractor apart and the 2 piece neoprene seal and side packing out. Everything looked good with the seal so I don t see why it was leaking. No trash or silicone in the seal and thank goodness the bearings looked great. I was afraid maybe I had spun a bearing.

The crank had some slight pitting on it. It is not as bad as the photo looks. I don t think that was the cause of the leak because it ran for a long time before it leaked, but then who knows. How do I fix the crank pitting while waiting on a Victor seal kit?

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Your problem is your crank. In between where your rear main seal rides, and where the bearing rides there is supposed to be a sort of a flange that is approx. 1/8 inch thick and sticks up about 1/2 inch from the bearing surface. It rides in the groove that is just forward of the groove that the seal fits into. It is a flinger that pushes the oil outward and into that groove and shields the seal from having oil thrown forcefully at it. That is why your perfectly good seal is leaking buckets. I can't tell you if this missing ring is machined out or welded on. I have wondered about this myself. Anyway, you need to take it to your local automotive machine shop and they will tell you if it is repairable or not and how much and whether or not you need to go looking for one. They are not hard to find.

Why does it look like a gap between the bearing and crank...

Looks rough to me a rope make be all you can do...

The only set like that I have used the only way I could get it to seal was put RTV on the side seals... I am not crazy about'em...

I have had to replace the crank to get them to stop leaking BUT the crank needed replacing anyways...

Good catch :wink:

Showcrop:
I have seen some crank shafts with the flange (oil slinger) on them. I do not think this model had them, or at least I can not find one even in the parts manual.

HOBO NC

Why does it look like a gap between the bearing and crank...

I took the bearing cap off and loosened everything up to see how far the crankshaft would come down before I removed the seal.

I thought you pulled the engine... My bad...

(quoted from post at 08:47:13 05/06/19) Showcrop:
I have seen some crank shafts with the flange (oil slinger) on them. I do not think this model had them, or at least I can not find one even in the parts manual.

Click to expand...

Don't know what to tell you. The crank in my 901 had one as I described, as does the Datsun motor that I am just finishing up now. They were both part of the crank, whether pressed on, welded on, or machined out. They would not show up separately on a parts digram or list. The groove in the block and cap is there to accommodate it, and the result of not having it I think is apparent.

It also has a place machined in the block for it...

I don't understand the hesitance to use a rope seal. They work very well for long periods of time when put in correctly. I like them better than these cheap new seals. You do have to work them in before you cut them to length then cut slightly long so they compress into the bearing cap.

(quoted from post at 04:47:29 05/07/19) I don't understand the hesitance to use a rope seal. They work very well for long periods of time when put in correctly. I like them better than these cheap new seals. You do have to work them in before you cut them to length then cut slightly long so they compress into the bearing cap.

Click to expand...

Caterpillar guy, I have put a few in and I would describe it as a little more than "work it in" to do it correctly. That is why I always recommend anyone watching that video of installing one in a Holden V8 because it is so complete and step by step.