View Full Version : Help and ideas with pinhole leak in 351 block

john jones
06-02-2013, 12:22 AM
Without going into a long story.. Last year I bought this 93 Maristar with 351 indmar 250 hours. When we were test driving it I noticed that there was oil dripping down the bell housing on the transmission. I told the buyer that it was probably a rear main seal. Seemed reasonable he hadn't used it for 2 years after his wife died. We negotiated the price and I bought it.

Fast forward to this week, I decided to replace the seal. I got it all done we took it out for the test drive today. We were motoring around I am looking to make sure everything looks good. As I was patting myself on the back and high fiving my wife, I took another look and noticed oil on the bell housing. Damn I was so careful what happened?? As I am looking again she is on the gas and around 2000 rpm and I notice oil coming out of this pinhole (I am not kidding, it is a pinhole) traveling along the top of the oil pan gasket and dripping down the bell housing.

So, I am looking for repair options. Has anyone tried this? If so, what did you use to repair? I have read about guys drilling above and below the crack and filling with epoxy, marine tek, JB etc.. To be honest it is so small drilling looks like it would cause more of a hole than what I have currently.

I have attached a pic. It is the best i can do with my cell phone camera.
the arrow shows the pinhole and the oval shows the oil running down the block. This only happens when it is at high rpms 2000 and above.

Thanks for the help..

06-02-2013, 01:38 AM

06-02-2013, 09:58 AM
Sand down around the pin hole, zip with welder and then repaint... should be good to go and hold better than jb weld

06-02-2013, 10:45 AM

06-02-2013, 11:22 AM
Yes you could weld it, but is there a larger void behind it.

As a boilermaker and somebody who has done plenty of NDT, I would recommend that you consider braizing the pin hole, second choice weld, but to temper this I would say both would be fine.

06-02-2013, 11:57 AM
I say skip the JB and just stick some old bubble gum over it.

john jones
06-03-2013, 12:26 AM
Thanks for the ideas. I will try and find a good marine welder who feels certain that he can fix this. Glad to know that there are some options.

Anyone have any ideas how this could happen? I understand if the water isn"t drained the block can crack when frozen, but this is oil coming out of this pinhole.. Any ideas?

06-03-2013, 09:30 AM
Sounds like a void from the casting process, rare, but can happen.

06-03-2013, 09:57 AM
Is there anything clogging the crank case ventilation??

john jones
06-03-2013, 05:39 PM
Is there anything clogging the crank case ventilation??

Not sure? I took the pcv valve out of the rocker arm cover, looked it over. It appeared fine. Is there another way that I can check?

06-03-2013, 06:02 PM
Not sure? I took the pcv valve out of the rocker arm cover, looked it over. It appeared fine. Is there another way that I can check?

Shake it.....if it rattles it's be good.

john jones
06-03-2013, 11:53 PM
PCV valve is good.

I called around 6 marine shops in the Portland area. I was told to change out the block by some. I was also told by others to use JB weld. I asked about someone who could weld on Cast and no one knew anyone.

Does anyone know anyone in the Portland area that could do this?