Bad Day 396

[cheveslakr]

Long story......I've been storing the numbers matching L34 out of my convertible forever and since I've decided to finally put some miles on it, I'm upgrading and fixing anything that's nagging. So, a few summers back, I rebuilt the 396, couldn't find a piston that was anything less than .025 down the hole, so I cleaned the deck as good as I could, block sanded with 150 grit, then assembled with a shim gasket. That measurement could have been .030, I don't write stuff down. I remember cringing at the thought of a .040 head gasket though. Well, fast forward to today, finally got the thing on the run stand, fired it up, everything went well....about 2 minutes in, at 2500 rpm, noticed steam coming from the headers.....shut her down. Those shim gaskets were leaking front and back, both of them. So, I know what I'm doing this weekend...crap.

Oh well, things like this don't get me down, just another step, and lesson learned.

This is for the convertible, it's getting the correct engine, correct master cylinder, new SS brake lines, correct power steering brackets, alternator brackets, refinished driveline with coded stripes, fixed a stripped rear lug nut, and a couple things in the interior corrected. This little engine should be impressive compared to the other 396, possibly another 100 hp. We'll see.

 

[77cruiser]

But better there than in the car. I wish I would ever get around to building a test stand.

 

[cheveslakr]

It's crude, but yeah, this is the third engine I've broken the flat tappet in BEFORE installing in the car. Just rigged up a slider stand that sets on the legs of my cherry picker. I pick it right off their, drop the cradle, and set it in the car...works slick. Also, it' saves space which I have very little of.

 

[Nashville Cat]

Very nice. Can't wait to hear it run !

 

[Shovelrick]

Here's a pic of some really good sealer for shim gaskets, I used SS brake lines and would Not do it again, harder to get to seat or seal than the nickle/copper I think it is? or another bimetal thats pretty good at not rusting

 

[cheveslakr]

Yeah, I've read all I can on the shim gaskets, and have used them on a 283 with oem finish on heads and block....no issues. These gaskets specifically say not to coat them, they come with their own coating. So I didn't....and they failed. I bought 4, 1 set for the plate hone, which my machinist never used as he had a set....so I have another one to use IF I can be certain they won't fail again. Nothing I've heard directs me to a mistake on my part, so I'd be foolish to repeat the process. Now, if someone told me they had the same problem and sealing the "pre-coated" gaskets cured that, I'd be willing to try the other set.

 

[kmakar]

I'd be suspect out the gate and would consider sealing them if the same set leaked when you put them on. I know from experience that most are pretty careful as mistakes during this stage can have catastrophic effects, and truth be known, I'd trust myself (meaning you) if you knew you did it right. Can't offer what to do, but go with your gut feeling.

 

[68Chevele]

I always use Hi-tack sealant on the shim gaskets, never had a leak.

 

[cheveslakr]

Okay, those that have used sealant and had success, the questions that must be answered are.... what was the finish on the block and the heads? Were your gaskets pre-coated? Did you check the flatness of your block if it wasn't decked?

 

[cheveslakr]

Tore it down today, wet head to toe across the head surface. All broaching is evident, so confident I didn't compromise the sealing surface from factory. Brought piston up to tdc and measured .031 down the hole, this triggers my memory, and I'll write all this stuff down this time. That's the reason I chose the shim gaskets. Gaskets felt non-tacky. So I grabbed the other set of Mr Gaskets, since I bought 4...they're dry also, non-tacky. The last pair of shim gaskets I used on my 283 had a very tacky coating on them out of the wrapper, I used them as is and had no issues. Clearly, these needed a seal coat, even though the directions say not to. Bunch of bs, but I should have questioned it before I installed. I've got pics, but they won't load, so I'll post when they do. So, I've got 3 options....1, seal the other set like suggested, gaskets and block, head surfaces and repeat. 2, buy a different set of shim gaskets from another supplier and avoid the Mr gaskets. 3, buy the thinnest composite gasket I can and settle for a .068-070 quench, which I want to avoid.

 

[cheveslakr]

Think I'm in a happy place with this. Broke the cam in today, intervals of 7 minutes or so and this little seepage was evident but after the 2nd cycle, it didn't seem to get any worse. This was all gasket sealer, no coolant. Process I took.....same brand gaskets, sprayed both sides with permatex copper sealer, bought a straight bar, checked the deck and I couldn't slide a 1.5 thou feeler gauge anywhere in anywhere across the deck, measuring at diagonals and straight across. Torqued bolts in 3 series, then checked again....found the upper row needing a tad big more stretch. Happy now, and can move forward and very greatful to all that chimed in!!

 

[kmakar]

Yep, I could live with that. Great job, now get into that car!

 

[cheveslakr]

Oh, I wrestled with this issue for days before I decided the next move. Stressed for sure not knowing what I did wrong and not willing to be defeated twice. Big relief!
There was varied advice, mostly good and glad I asked. Saving deck numbers just plain sucks in the grand scheme of performance.

 

[cheveslakr]

Pulled the old 396 today and so made the right decision since this one needs a bit of attention. Had this happen once before in a bbc, the thing sat for 28 years, putting maybe 1000 miles on the car. I ran it for 20 min or so a couple times a year, and maybe drove it for 5 miles each year for the past 15. Not what I call taking care of a chevy! Honestly thought about selling so many times, but it's just too sweet of a car. I've promised to give it more quality time from here forward.
The coolant came out beautiful in all orifices but the lower block drains, the pass side wouldn't even flow till I dug it out with a screwdriver, then brown corroded crud for a couple secs followed by good clean coolant. The rear freeze plugs were so corroded, 1 was easily pierced with a pick, so they're coming out. I'll do a thorough flush and then treat it with this stuff...
This is a great idea for any car that sits, so I'll be adding it to the coolant in all my rides.

 

[Pete 67]

I answered your thread on the OCS but not here...I can't seem to keep up. Glad the copper spray worked out for you. I used it on my L79 build, & I'm happy I did after hearing your story. My problem is a seeping timing cover seal, that I should've used a thicker coat of sealant on. Sometimes I hate this shit. sigh.

Anyway, which car is this 396 going in?

 

[cheveslakr]

Yeah, sometimes the switching back and forth is a bit much, so I concentrate on this site more and more. Kind of like the kids with split parents huh
Anyways, I hate leaks, and each surface requires it's own method. For me, tin gets a paper gasket, coated both sides with a skim of gasket sealer, snugged, then torqued the following day. Intake gaskets get the good felpros, loctite anaerobic sealer around the coolant passages, very thin. I've always zero decked and used a comp head gasket, cometic on high perf.
Making sure you've got a good functioning pcv or crossthrough ventilation is key to keeping the leaching to a minimum.
This is going in the convertible, had the car since '97.

 

[Pete 67]

Yeah, sometimes the switching back and forth is a bit much, so I concentrate on this site more and more. Kind of like the kids with split parents huh
Anyways, I hate leaks, and each surface requires it's own method. For me, tin gets a paper gasket, coated both sides with a skim of gasket sealer, snugged, then torqued the following day. Intake gaskets get the good felpros, loctite anaerobic sealer around the coolant passages, very thin. I've always zero decked and used a comp head gasket, cometic on high perf.
Making sure you've got a good functioning pcv or crossthrough ventilation is key to keeping the leaching to a minimum.
This is going in the convertible, had the car since '97.

Yeah I follow the same steps you do, basically. The cover seal that's leaking is the front lower one that connects to the pan gaskets. It must've slid a little while I installed the pan. I managed to squeeze a bead of sealant in the gap to stop it, but it still pissed me off when I feel like I did everything right.

 

[cheveslakr]

Gaining on it....waiting for a water pump and it may be months, but hope sooner. If it wasn't for the numbers, it'd be done!

 

[68Chevele]

I bought a GBN water pump form Rockauto for $37 brand new, my 461 ran way cooler with this one over the factory pump that started to leak. Now I have a new electric one for the race car.

 

[Nashville Cat]

Gaining on it....waiting for a water pump and it may be months, but hope sooner. If it wasn't for the numbers, it'd be done!

Ever considered keeping that original block in the garage corner and buying a 4.25" bore block to run ?
Love 427's !