My GMC 302 has developrd an oil leak. I installed a new front and rear seals 3 months ago while installing a 200R4. Unfortunately the rear seal is leaking worse than ever. I am trying to decide what to do now.
One option is to just remove the oil pan and the lower half of the rear main bearing to replace the seal. This saves a lot of effort but but will this approach work? Has anyone tried this? This might be worth the effort if this has a good chance of working.
The other approach is to remove the entire power train, put the engine on a stand, remove the crankshaft and replace the entire rear seal, and put the whole thing back into the car. This approch i know has the best chance of success, but will take more time and $$.
Another thing I am wondering about is the best way to install the rear seal or half a seal. Please help me decide if you have any experience that you may have had doing this.
The GMC manual says to lay the seal rope matrial into the groves in the block and cap and use a wooden mandrel and hammer to press the seal into the groves. The GMC manual pg 377-8) also says to cut the seal ends with a sharp knife and don't leave any frayed ends which would prevent proper seating of the bearing cap to the block ( and cause leaks). I have a friend making a mandrel now.
The Instructions from Best Gasket are very different. They say drill a 1/16 hole in the bottom of the bearing cap to insert a pin provided so that about 1/8 inch is showing to insert into the seal, or use Ultra RTV sealant across the length of the rope to keep it from shifting in the groove. The other thing is to cut the rope ends using a 0.015 in spacer to add material above the bearing cap and block serface but to pack it down flush and push any loose strands toward the center before tughtening the cap down.
I added 0.015 to the end of the rope but it is now leaking. Maybe some stray rope strands got between the cap and block?
I've done it but ways and like everyone else had mixed results. Years ago I heard of someone using a MOPAR neoprene rear seal but I think it took some machine work before the engine was assembled. I have had good luck with Best Gaskets and their method. When doing it from under the vehicle I loosen the mains to take the load off of the top half and I leave the stick-out on the lower half because it is hard to trim the upper. I have gone as far as taking the timing cover loose and sliding the tranny back to gain more room on top. I think it comes down to whether you want to try to fix it or whether you want to redo it.
"I wonder if God created man because he was disappointed in the monkey?" Mark Twain
I used BEST rear main and also added the pin to the lower rear bearing cup. Works well. The key to rope seals is packing the ends in tightly. I cut a drum stick end into a square and used a bearing seal packer together with the drumstick "pusher" to pack the rope as tightly as possible before cutting it.
I have used the Graphtite seals from Best Gaskest. In my experience there is always overflow trapped between the bearing cap and the block - I always remove and tighten the cap several times and use a razor blade to cut the frays till it bolts clean with no bulges getting pinched.
In your case the upper seal already in place. I would use a piece of dowel rod to pack the exposed ends of the upper part of seal. Tap the dowel with a hammer. Then install the bottom half the rope seal as described in the instructions but trim it long enough to fill the voids left on the block side - plus the .015 extra. Start the cap bolts but leave them loose so that cap hangs on them. Slowly draw the bolts up toward the block making sure the extra on the ends are going in straight.
Tighten snugly and then loosen slowly allowing the cap to come straight down. Once the tails are clear of the block take the cap all the way off and inspect for pinches on the face of the cap. There shouldn't be any on the block side - but make sure it is clean. Trim accordingly and try again.
The pin is used to make sure the seal doesn't spin. When installing start in the center of the rope seal pressing it down on the pin and then work from the center out.
