Hi guys, Like many before me, I have a leaking rear main seal in a 350 SBC... It's a "Hencho en Mexico" 350 Blueprint motor bought and fitted by a previous owner. I recently replaced the clutch and as a precaution also replaced the rear main seal and the pan gasket. There was a slight leak from the back of the engine, but nothing too bad. I did it with the engine in the car. When I removed the rear main I was surprised to find a Felpro 2909 seal in there. This is the oversize seal for align honed 400 SBCs. As these seals are unavailable anywhere globally, I used a standard Felpro 2900 to replace it. The crank and the external seal areas measured within spec for a 350. There was a slight wear line on the crank and the new seal seemed to slide in quite easily. I followed all of the recommendations for seal install (offset ends, RTV on ends of seal, sealant on main cap, used plastic install tool etc etc.) After running the car for 30mins it appears the seal is now leaking worse than before!! Could someone have used the 2909 seal to try and 'tighten' the seal on the crank to prevent leaks?? I'm not looking forward to pulling the car apart again, so should I try and find a 2909 (even though this technically shouldn't suit my engine)? Has anyone or heard of this modification before?? Thanks Dave
It looks like the Fel-Pro 2909 is possibly available though Jegs Fel-Pro 2909: Rear Main Seal SBC large outside diameter | JEGS Can't say what a machine shop may have done when they "blueprinted" the engine block but they may have machined the seal area to save a damaged block. A lot of those Target motors got stuck in bob tail trucks in fleets and beat on pretty hard. Then if they were sold as core motors after that you get what you get.
When you align honed a 400 it opened up the rear seal bore because the 400 main size was bigger than the seal bore on a 350. If you align bored the 400 you didn't go through the rear cap seal surface so you could use the std 350 seal. The quick fix was to use a tie strap under the seal to make up for the removed material until they started to make the 2909 rear seals to compensate for the larger bore. Why a 350 would need a 2909 is a mystery or is it really a 400 block?
Thanks for the response ottoman! I wondered if it was a 400 block, but the casting number (10066036) and the two welsh plugs on the side suggest it’s a 350. I measured the seal bore and it was approx 2.75” (I can’t find where I wrote it down). The 2909 suits a bore size of 2.84”. Do you think I should find a 2909 and try that? It’s a major hassle to replace it, so I’m not sure what to do...
I kept it for reference, but half of it has been destroyed when removing it! I probably shouldn’t have touched it...
Thanks for the response! JEGS and Summit have confirmed nil stock. I wonder if it was a high mileage or damaged core. The seal bore size was in spec for a 350, so not sure what to do next...
Brit speak for nothing. mostly heard in soccer matches broadcasting. The score of 1 - 0 is one nil LOL
After reading the whole thread again a .090 difference would mean that the 2009 shouldn't fit in the block without issues unless the block had indeed been altered. Have you checked the main bearing numbers on the bearings to see that they are standard OD 350 bearings? I used to engine and head install work in a cylinder head shop that would put undersize ID valve guides in engines and then machine the valve stems on the old valves down a few thousandths to fit to have new wear surfaces on the valve stems. That worked until someone in the field needed to replace one valve at a later date and the guide was undersize. I am thinking again that this block has had some changes made by the machine shop to fix prior damage that would call for scrapping the block in a lot of shops.
Why not shorten the seal spring a bit? They have a joint where they are put together. Cut some off the female end and screw it back together. Screw spring left to take apart and right to put back. It is not to hard to find the joint.
2-piece seal , no spring. I doubt any sort of sealant will help if you're " rolling " the seal in place . If , however , you were to remove the crank where you'd the be able to " place" the seal into the sealant , it might work
Also make sure that the crankcase is venting properly. If there is a build-up of pressure in the crankcase it will try to push oil past the rear main seal . . . or any other gasket or seal for that matter.
The Jalopy Journal
