Vibration / Rear Main Seal leak on brand new engine.

[Chillin014]

I've been enjoying my freshly re-built 400 SBC for about a month now, probably put about 1000 miles on it. Recently I noticed upon cold start-up quite a bit of oil was coming from the transmission bell housing. After further inspection and removal of the transmission/ clutch/ flywheel, it is definitely coming from the rear main seal.

About the same time I noticed this leak, the motor also seemed to have a very odd vibration. It is steady through all RPMs and just feels like the motor FELL out of balance. I spent probably 3 grand having this engine built / balanced and everything and it felt perfectly fine for the first few weeks. I at first thought the vibration was the exhaust because I just installed racing mufflers, but it feels like its coming from the engine itself.

Yes I have brand new motor mounts, yes I have spark plug wires in the right place. This is not something that happened after installation of the engine, this happened weeks after having a perfectly fine running set-up.

My other thoughts are that I have been running an old clapped-out T-5 behind the engine and I started to wonder if it or the clutch were causing a balancing issue and maybe causing wear on the crankshaft? I know rear main seals tend to go bad when the crank bearings wear out so the combination of this vibration and the oil leak is really worrying me.

My engine is covered under warranty at the machine shop but pulling it back out isn't exactly an appealing option so I figured I'd post up here and see what everyone thought. I wish I had just put an LS1 in the thing now for how much money I've spent.

thanks for any advice

 

[bowtie81]

transmission mount, driveshaft?

 

[464elcamino]

Balancer tight? Did the shaft on the trans go into the pilot bearing ok , its possible it got hung up and is pushing the crank forward and wearing out a journal , kinda like when a auto trans ballons a converter and shoves crank forward. I would lean more towards something on the back side of engine versus the front/balancer unless front seal is leaking as well. Also when the flywheel was installed were the bolts the right length? Hope ya get it figured out bud.

 

[Chillin014]

Uh oh....I actually just realized neither the machine shop nor I installed a pilot bearing at all. So that seems like a very probable candidate. I guess I might as well pull the motor tomorrow and see what kind of damage has been done. Could a bearing wear that quickly? I wonder if the crankshaft journals will have to be resurfaced too....ugh!

 

[464elcamino]

You might get lucky and replace the rear main and pilot bearing, I just hope that if this is the problem that it didnt hurt your trans shaft that rides in the bearing or waller out a bigger hole in back of crank where the bearing goes.

 

[Chillin014]

I bought a brand new transmission, so I'm not worried about the transmission. I dont think it hurt the pilotbearing housing in the crankshaft either as that hole is considerably larger than the transmissions input shaft. My main concern is that I'm going to have to remove the crankshaft. If the damage requires resurfacing, I wonder if it would be more cost effective to buy a brand new crankshaft and bearings? Is it okay to replace the crankshaft with the pistons and rods still in the block? Like I said, everything was balanced together as a rotating assembly so I'm very weary about changing anything.

 

[D&A Machine Shop]

Yes you can change a crank with the engine assembled, its not fun but it is doable.
If you have to change the crank then the new one will need to be balanced to match the old one.
But before you go that far I would cut the filter apart and see if you have any bearing material in the element.
Also you could pull the transmision and clutch then fire the engine and see if it still vibrates, if it does then pull the engine,
If the vibration is gone then at least you know it was the pilot bushing not being in there that caused the problem.
You might be able to pull the pan with the engine still in the car so you can change the rear seal, while the pan is off you can
check a few bearings.

 

[79wagonator]

You didnt mention if you used a new harmonic balancer on the motor. or did you reuse the old one?

 

[Chillin014]

Thanks guys. The harmonic balancer is brand new and it was all balanced together including the flywheel.

Okay I guess I will go try to start it up without the transmission one more time, I messed with the distributor the other day so it was becoming very hard to start and backfiring out of the carb. I'll also cut the filter apart and check that as well. I'll be back with more information later today.

 

[D&A Machine Shop]

Dont forget to pull the clutch. If the pilot bushing is not in there then the input shaft will not line the clutch disk up and it will still cause a vibration.