VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Update on 1941 rear seal and PCV valve

I have now two sets of original rear seals. One set in the picture was from Mike Deeter who kindly sent a set so I could compare them with the two sets I bought from Gasket City. I would strongly recommend contacting them if you are experiencing rear seal issues and want to replace yours with an original set.



Mike Deeter's theory is that the Best graphite seals are leaking at the top not the bottom. He believes that the bottom seal is compressed more by the weight of the crank. You can see in the next two pictures that I was able to slide a .003 feeler gauge between the block and crank. I was not able to do the same on the bottom. This could have been because of Mike's theory or because I had a shim behind it? I am demonstrating this on my 49 engine which leaked excessively.




The next picture shows how I finally sealed the valve cover so as to maximize the vacuum of the PCV valve. The results of that are shown in the next picture. It shows I still have an oil leak but not as severe as the original one.




The machine shop has agreed to install a set of the NOS rear seals. I will start tomorrow on removing the engine. I stuck a window air conditioner in my garage window and will watch the British Open on TV. Guess you have to take the "good with the bad, " or is it, "bad with the good?"

As frustrating as this journey has been, at times, I could not have done it without all your help. Best wishes, Mike

If you seal off all the vents a positive vent system or any other vent system It WILL NOT work. There must be fresh incoming air from some source. Positive vent was standard on some trucks and optional for all vehicles. It took in air through the valve cover vents till 1955- Then the vents were eleminated and the intake was through the vented oil filler cap. It 1968 they changed to a closed positive vent system. The air intake was then mounted insude the air cleaner and took in filtered air through a special mesh.....less dust injested.
The crankshaft will be pushed down when the engine is under power. That is why the rear main must be adjusted on the "tight" side to better keep the shaft centered in the main journal to prevent leakage.

The positive vent system was used originally as a way to vent the crankcase when the vehicle was not moving. The road draft system worked fine at 35 MPH and up but trucks and cars that were used under conditions where the engine did a lot of idleing there was no venting taking place and the engines would sludge up. The reason it was used from 1963 and up for all engines was to burn up the "blow-by" fumes that came out of the road draft tube - an air polution thing.
If your road draft tube is clear (they did fill with sludge) there will be not more pressure in the crankcase than there is with a PV system. The pressre is the highest when under full power and thats why you used to see the center of the traffic lane black from blow-by and up hill grades.

Thanks Gene, so I am assuming that I should leave one of the valve cover vents open as a source of fresh air?

As I understand it, when I talked with the shop foreman that did my rebuild, he stressed that the PCV system works only with the right size PCV valve and the correct mixture of vacuum to fresh air. If there is too much fresh air entering through the valve cover vents or an unplugged breather tube then the thing doesn't work.

I am suspicious about the postings of those who have adapted their cars/trucks to PCV venting. How did they do their engineering to establish the right vacuum/fresh air ratio. Plugging up the breather hole in the block, or the breather tube does eliminate the possibility of oil leaking from a breather tube but is it really recirculating crankcase gases back into your intake manifold?

In defense of my shop foreman who is in his 60's with plenty of engine rebuilding experience, he has never hesitated in saying that the rear seal needs to be replaced, but has also been curious about the effect of PCV venting for solving a rear seal leak. Thanks, Mike

If I were going to install a PCV system on one of my cars I would try and find the GM setup that was sold thru the parts departments or find a motor from a big truck that had it installed. My 53 6400 Firetruck has a PCV system on it. I don't think a PCV installed will make any difference caused by a leak that is a result of a worn engine, excessive clearance in the bearings or a defective seal. Gene explains in his post very clear how a PCV system works and how a draft tube works. It might be a good idea to find someone with a dye kit to help check it closer before you take it apart. It's easy enough to put the dye in and then use the black light to check and see where the oil is coming from. If you do it don't run it anymore than you need to and don't drive it very fast so it sprays the dyed oil all over, makes it unless to see the source of the leak.
Good luck
Don

The pv system amounts to a small vacuum leak. This will lean out you fuel/air mixture and could affect engine performance and or burn an exhaust valve.
There is nothing wrong with the original system. It can relieve more pressure from inside the crankcase than a PV systemm can. When the caused a problem a caused oil to leak is when the road draft tube became plugged-up. The short coming of the original system was it failled to provide adquate venting in the winter when the car was used for short trip city driving. It performs perfectly well for the driving our old cars recieve......I would stay with the original, make sure the road draft tube is clear (fumes should be coming out at a hot idle) and the vents in the valve cover are open.

I don't understand the logic of the crank sitting on the bottom of the rope seal. I would have thought the bearing would have kept the crank in the proper position. If your crank is dropping down that much, I would imagine there's way too much slack in the main bearing. Something is not lining up right and I really don't know what it is. So far, my Best Gaskets Rope Seal is holding strong and dry.

However, I do think you're going down the right road by installing another rope seal. Maaaaybeeee this one will hold...I sure hope so anyway.

Say the bearing has .002" clearance. Under power the crankshaft has a down force placed on it. The the clearance on the top would be ..0015" and the bottom .0005".....The space between the seal on the top and bottom would be the same measurments. A rubber or lip type seal could flex enough to cover that amount. Thats why it is important to have the bearing adjusted "on the tight side".
All things considered with the above numbers and a properly installed rope seal there would be next to no leakage. All seals need some leakage to lbricate the seal its self.
A properly installed rope seal did not leak. They were used on Oldsmobile 307 engines up till the last one made in 1990.

There was a fellow here, now deceased, who was a certified wizard on engines. He started with T Models and went through approx 2008. He built full race flatheads for whisky and dirt tracks, Jimmy 6 cyl's and overhead Chevie V/8's for NASCAR. Self-taught, he had a lot of secret tricks.

I'm told one of his Chevy engines still holds the lap record the last time they ran Daytona on the beach (likely driven by Joe Lee Johnson).

***When he built any engine with a rope seal (and there were a lot of 'em) he positioned the seals with the ends at top center and bottom center (not at the sides). This must be difficult to accomplish. I don't know but he likely sealed the ends of the rope with something. His engines didn't drip at the main bearings seals!

Just a FWIW.

The machine shop foreman came and picked up my engine head and block last Monday. He called the next day and asked me to bring in all the remaining parts including the radiator so he could start the engine after replacing the rear seal. I was out of town so brought him the parts today.

The pictures show the condition he found the seal in. He said it was completely saturated with oil and had moved about 60 degrees from where he had originally installed it. Remember the pin holding the seal? It had left a cut in the back of the seal as it moved. It doesn't show in the first picture because I took a different area. Notice how there is a fine irregular ridge on the top and bottom of the seal. In my earlier posts some of this edge was sticking on the back of the rear bearing cap.

I assume the complete failure of this seal could have been caused by excessive heat or over compression of the seal, or both?






He was also very concerned that the remaining oil in the oil pan was contaminated with gas when he took the oil pan off. I had saved the oil I drained and to me it smelled like burnt oil. He said the entire crank and cylinder walls etc. seemed to be dry, when they should have had an oil residue feel to them. He showed me the cam which had the beginning of wear patterns but yet no grooving. He felt this was unusual for having only 100 miles on the engine. He then showed me the fuel pump which you can see has an extremely worn cam driven rocker arm. He assumed that this was another sign of gas in the oil. The arm should be as it appears in the last picture.

He assumed that the gas in the oil was caused by a flooding of the engine on original start up, or the carburetor was malfunctioning. He asked that I rebuild the carb. Being in a hurry I did a partial rebuild finding the float level 1/8th of an inch from parallel (sagging), and the accelerator pump with badly damaged leather. I replaced the accelerator pump, float needle and seat, upper pump cylinder gasket, and the bowl cover gasket. I also checked the low speed jet. I hope to hear from the shop latter this week. Thanks, Mike

P.S. The float needle was also the old style (all metal).

Seeing you have a new camshaft use Quaker State Defy oil . It contains more zinc for break-in. The best price I saw for it was at Walmart.
The seal looks like it was not installed fully in the grove. Was that an existing fuel pump or a brand new one. Looks like poor hardening of the wearing surface.

Hi Gene, The fuel pump was a used one that I had used on the 49 engine. I do not remember its original condition, but think as you that it lacked harden steel. I looked through my extras and sent him (through the CarQuest delivery system) two to choose from. Time will tell, Mike

P.S. Thanks for the oil suggestion.

I would suspect the pump arm was worn when installed on the rebuilt engine. It is not unusual to see some wear in that area but not that much.
I was thinnking back to when the engine was first started and squeaking. The squeaking was caused by the excessive gas wahing the oil from the cylinder walls.
When you restart it this time don not use the choke so it dosen't load-up with gas so fast. If it were mine I would jump it with 12 volts so it would get runnig faster with les chance of flooding.
I am sure running it for 100 miles with a little gas in the oil did not harm anything. Just hastened the break-in a little.
Keep us posted....good luck

The groove that your rope seal sits in appears to not be round. The more I read about your engine, the more I get upset about your machine shop. No one is perfect but gosh...what a mess! Fuel in the oil? I've never heard of such. Premature wear on the cam? What the heck! I don't understand. I still think your rope seal problem goes back to when your machine shop decided to make adjustments to the roundness of the groove that holds the seal.

I had my engine machined at a machine shop, then my dad and I assembled it....we're just shade tree mechanics. We shimmed all the bearings which took a day or so. It was a lot of work and we did have a few problems along the way. It just bothers me that you spent a great deal of money on your engine and it appears your shop screwed it all up.

As for your shop saying that a Best Gaskets Rope Seal won't work....I've got 400 miles on mine now and not a drop. I drove from Knoxville to the big show in Somerset, Ky last Saturday which was 108 miles one-way. I drove 60mph with no issues and had a heck of a lot of fun. My engine is all original and it works well. I don't have a PVC valve or anything else special. Just a plain ol 216.

I hope your shop finds a way to make things right. Gosh I hate what you're going through on this. I'm really sorry you're having so much trouble.

Tomorrow I should get my engine back from the machine shop. They have run the engine for over 3 hours without any sign of the rear seal leaking. They did find a carburetor problem which I solved by bringing them another carb. The engines (1949,1941)that I have used, since the day I purchased the car in 2003, have had an irregular quiver I call a miss. At high RPM the quiver seems to go away. My gut feeling is that what has been common to both engines is my distributor, and vacuum advance. One of the shop mechanics thought it could be a pin leak in the vacuum advance? I have other units so I will give another a try. I also have other distributors so will make a switch. I am excited to put a lot of miles on the car before winter to confirm the rear seal is finally not leaking. Thanks, Mike

P.S. This winter I hope to switch frames, which at my speed I am projecting two years to complete. Part of the time will also involve body work on the firewall and driver side rocker panel.

That is great news and it is very impressive that your shop would do that. Those are great photos too!

Looks like the shop stepped up and are trying their best to make the job a first class one. It is sure heartening that there still are people that will stand behind their work even it if means more time and funds from their pockets to make it right. Seems there are fewer of those people today.

I spent nearly 30 years in customer service and am constantly amazed how pitiful customer service has become in the USA. When the bean counters take control then "service" suffers.

Are you sure they put oil in it

Drove the car about 45 minutes last evening. The engine has about 5 hours on it now and there is absolutely no sign of oil leaking from the rear seal. Its easier to mess with the distributor with the fenders off so will try to fine tune things a little more before putting things back together.

I have two other distributors/vacuum advances so want to give each of them a try at eliminating a slight miss that seems to have followed me from the 49 engine I replaced to this one.

Seems like I can see the light at the end of the tunnel. Lucky me, Mike

P.S. For those wondering what is in the bag on the firewall, its a rabbit's foot. Yes, we have big rabbits in Michigan, and I need all the luck I can get.

Mike,
I am extremely excited about the outcome. You have a good looking solid old car. I like it!

I hope you never have to drop the pan or pull the engine again....you sure have a lot of drive to go through the process so many times.

I'm glad they got you sorted out over there. Its no fun tearing down things twice... three times... four times... yikes! I've had issue with that shop once but they made it right so I continue to use them but it would have been better with no mistakes!