Just bought a 67 firebird with a 68 428 in it. The rear main seal was a rope style and it blew out the first time I drove it. Put it in the shop and installed a Butler Performance seal and the mechanic just called me and said oil was blowing past it like it wasn’t there. Any suggestions. He’s thinking possibly a worn crank
You have to remove crank to properly install seal. Pull engine and check other things while your at it. One short cut found more could be lurking inside.
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The one piece and two piece chevron style rear seals work well but have to be installed correctly. If the anti rotation holes in the cap and block are not cleaned out first then refilled with sealant before the seal is installed it will leak. It's best to install them with the mating ends just a few degrees turned from the mating lines of the cap and block. It takes two people to install the one piece, I've done the two piece by myself but better with two.
It could be you just need to reinstall a new seal but it's a lot of work, and $$ if you're paying someone else to do it.
Have the crank measured for straightness and out of round, if the seal area surface isn't round it will leak. They can be machined round but don't go through the directional knurls in the seal groove area. Some cranks had the knurling so deep they chewed up some seals.
The crank will have to come out again and the seal groove cleaned. Really cleaned. You should, or have the mechanic, test the seal groove in the cap/block for an out out round condition. Not so much with the small journal cranks, but the 428 and 455 had some blocks with a grove seal that was wasn't true. That can be really bad if a replacement cap is put on. The diameter of the seal groove is measured at the 12-6, 1-7, 2-8,....5-11 positions, if it's out by more than a few thou. the groove will have to be machined. I have the tolerance specs for the groove someplace, I'll try to find and post it.
If the main line has been bored it may have caused a non circular condition in the seal groove. When the mains are bored and honed the mating surfaces of the caps are shaved then installed and the bearing bores ground to size. The distance from the center of the bore to the bottom of the groove in the cap is shortened by the amount the caps were shaved. Some blocks have had the mains bored more than once. That can result in the groove in the cap being tighter to center than the groove in the block.
The sad part of this is trying to find a machine shop that will restore the groove for you. Mine was out 16 thou., due to not very professional work by the machine shop I'd taken my block to. I'd replaced my rear seal three times before I measured the groove and found the out of round condition. That was a few years back and I still kick myself for not measuring the groove before I started my build. I measured everything else, which is how I found the machinist bored the mains too large and shaved the caps at an angle other than 90 degree. The bore was bored three times by the time the mistakes were corrected. That resulted in an out of spec rear seal groove. I phoned every machine shop I could find on Vancouver Island and 10 on the lower mainland trying to find someone who would machine the seal groove. Not one would even try. They all said sure until they found out it was a Pontiac and not a chebby. I found a guy in Tennessee, I think it was, but shipping would have cost the same as replacing the block. I eventually made my own tool and bored it round myself. Machinists used to love problem solving, figuring out how to get something done. Now they push buttons on a keyboard, no program for a Pontiac seal groove so they can't do it. If your seal groove is what's causing your leak, maybe you can find an old time machinist to fix it for you.
Bluebird428 could you be a little more specific please? HaHa. That is great info. I’ll be sending this to my mechanic. He is an old school mechanic and really thought he had this one licked. I think it upset him as much as it did me. Now he has to pull this beast back out and figure It out. I am copying this info to send to him. Thanks again!
Another question. He also installed a high flow oil pump and said he wasn’t real impresssed with the oil pressure at idle while on his test drive(before discovering the rear main seal blown again). It was about 20#. What pressure should it idle at? He’s thinking there is potentially some leak by other places like the cam bushing/bearings but we will not know until it gets pulled apart again.
OK, now we have to know if your mechanic pulled the engine and just changed the seal or if he did any other measuring, rebuilding, fixing etc. Pontiac stock clearances are a bit tighter than a lot of others from the muscle era and usually have enough pressure to lift the relief valve with about 65psi at speed. 25 psi at idle is about normal in a hot engine, 20 is a bit low but a lot of guys have around 10.
Pressure is a result of a restriction to flow, the higher the restriction the higher the pressure as long as the supply source is able to keep pressure. Most Pontiacs use a Melling 54 oil pump. It flows enough to lubricate the engine with enough pressure and flow to keep it from destroying itself. As long as the bearings, main, rod, and camshaft are tight enough to restrict the flow, the pressure will be high. Stock Pontiacs only had about 1.5 thou. clearance on the mains. If the main bearings are worn to 3 or so thou the pressure will drop. Increase in flow will result in a higher pressure than a lower flow with larger clearances, but the stock pump should be enough to keep the pressure up as long as there is not an increase in clearance somewhere. If you have an increase clearance anywhere in the oil system the pressure will drop. The only way to know if you have a clearance problem is to measure everything when the engine is apart. The oil acts as a wedge between the bearings and the journals. The rotating member spins in the film of oil and doesn't touch the bearings, theoretically anyway. I think there are a few guys on this site that would be happy to get 20 psi at idle. Mine has 25 psi at 650 rpm in 100 degree weather at a stop light. I have 2.5 thou on the mains and rod bearings, I had to buy two sets of cam bearings in order to find bearings thick enough to give me the proper clearance on the cam bearings.
Your guy will find a problem, if there is one, when he measures the bearings in the bores and the journal size, but I wouldn't get to excited about 20 psi at idle. But if you have the engine apart anyway and he finds an excessive clearance the you may as well replace the bearings, if that is what the clearance problem is. If the crank journal is just a smidge small but you still get 20 psi, I would put it back together the way it is rather than grind the crank.
So either you are an amazing bullshi++er or the most helfpful person I have ever seen on a forum. These are very specific answers to not so specific questions. Thank you very much.
Well I have played poker on occasion, and If sitting in the pub with a couple pals talking about hooking Steelhead or Redfish on a fly, I may enhance the facts just a tad.
But!
I went through what you're going through right now, with my 428, not that many years ago. I tried just lifting the engine off the mounts and dropping the pan enough to change the seal. That didn't work. Then I pulled the engine and the crank to change the seal. That didn't work. Then I took it all apart and rebuilt it having the block machined and sunk a pile of dough into it. That didn't work. Then I pulled it apart again and measured the seal groove. I then built the tool and machined the groove. That stopped the leak.
At that time I thought I was done with it but only a few thousand miles later, one of the POS comp hydraulic roller lifters fell apart and I had to rebuild the whole thing yet again. I do have a bit of time put into the seal area of the 428 and I wouldn't bs about that.
I've since found that almost non of the engine rebuild shops on Vancouver Island will use Comp cams anything. I learned too late.
I think you will find, if you continue to use this forum, there are a lot of members with a lot of information here and they are willing to share. They have helped me more than I can repay.
Hard to say. I had the Best gasket in when the crank chewed it up, but that was due to the out of round seal groove. It was so tight it actually burned the crank and I had to polish it before reinstalling. When I re-did it I used the two piece BOP seal, worked as advertised. When I had to build it again after the lifter failure, I tried a one piece BOP but I couldn't get it installed correctly so I used a two piece.
Dave, over at SD Performance, recommends the one piece but says it takes two guys to install it. The one piece seal makes more sense and I would use that as long as I had someone to help me lay the crank.
I'll attach a photograph of the crank seal surface before I polished it. I don't think it would have mattered what seal was in there, it was going to leak with the seal groove that far out of round.