Problems with Recently Rebuilt 396

6

62BillT

Well-Known Member
A friend of mine had a 396 recently rebuilt through the shop that was helping to restore his car. The car was recently delivered to him and when he went to test start it himself, he heard some noise. He believes the Valves are hitting the Pistons. He was also told that the Block was Decked 60/1000 th's. I'm not an engine expert by far, but that sounds like a lot to me.

Looking for opinions, advice and/or direction.

Bill
 
62BillT said:
A friend of mine had a 396 recently rebuilt through the shop that was helping to restore his car. The car was recently delivered to him and when he went to test start it himself, he heard some noise. He believes the Valves are hitting the Pistons. He was also told that the Block was Decked 60/1000 th's. I'm not an engine expert by far, but that sounds like a lot to me.

Looking for opinions, advice and/or direction.

Bill
Click to expand...
FIRST......have the shop listen to it. You will want them to hear it before you do much of anything or they might want to blame the problem on your friend......if they are that kind. Plus it's only fair to them, they don't know what he could have done either.

What camshaft is in the motor ???

A compression check might tell you if it's possible the valves are hitting the pistons. It's NOT proof thou.

Do the following:

1 Bring the motor up to TDC on cylinder #1.
2 Remove a valve springs from cylinder #1.
3 Measure how far the valve drops with a dial indicator.
4 Repeat steps 1-3 at 10 BTDC
5 Repeat steps1-3 at 10 ATDC

NOTE: He will want to be very careful and make sure the piston is at TDC or the valve could drop into the cylinder.

 
Rick,

The shop is a 3rd party in a different state and there is a little problem there, but I don't know a whole lot about that part of it.

I'll ask about the Cam and relay the info that you have provided.

But I am still concerned about the 60/1000's Decking on the Block. As mentioned that sounds like a lot to me. Also wondering if they should have used thicker gaskets to make up for it.

Also it is a '66 396/325. Wondering if they were just Flat Top pistons originally?
 
My brother n law had a 396 built not long ago and it ended up the dome top pistons were hitting the head. You could rotate it by hands and not feel or here anything, but when it cranked it sounded like bad lifters.
 
.060 off the deck IS HUGE and in some cases means the blocks TRASH, the chances of the pistons hitting the heads is really good, obviously piston and valve clearance issues are also strongly suspect.
most un touched stock blocks measure 9.823 and in theory can easily be decked .020-.030 ,most shops try to remove .005-.015 on a clean-up deck cut, but it could require more, it sounds like that blocks been decked a couple times and yeah, if theres no problems .060 is doable, but that generally means the piston deck is sticking out of the bore requiring a thicker head gasket to maintain acceptable quench and piston to valve clearances, valve train geometry, etc.
now they do make head gaskets up to about .100 thick so theres a good chance that if nothing else is wrong that it might just be some new guy never measured clearances , slapped on a set of stock head gaskets and never gave it a thought. if it was my engine project I,d sure disassemble the whole engine and start measuring clearances because if who ever assembled the engine made that simple mistake theres an excellent chance that bearing side clearances, ring gaps,rod side clearances thrust bearing and other clearances were never verified and the assembler took parts and just bolted them together right out of the boxes they came from.
now that might seem to be a bit implausible but I see it rather frequently on first time engine builds

pulling it a part and checking NOW may be a P.I.T.A. but you can most likely save 90% of the components for re-use, something thats likely out of the question if the engines run for any length of time

these threads might help

http://garage.grumpysperformance.co...n-chamber-big-block-heads-and-casting-s.3960/

http://garage.grumpysperformance.com/index.php?threads/basic-396-bbc-build-video.13157/

http://garage.grumpysperformance.co...7-bbc-cylinder-head-choice-and-options.13247/

http://garage.grumpysperformance.com/index.php?threads/sources-of-bbc-info.752/

http://garage.grumpysperformance.co...402-bbc-with-a-4-454-crank-or-even-4-25.2165/

viewtopic.php?f=51&t=5460&p=16314&hilit=decking#p16314

viewtopic.php?f=69&t=2165

viewtopic.php?f=50&t=4925

viewtopic.php?f=52&t=181

viewtopic.php?f=53&t=2726

viewtopic.php?f=53&t=247

viewtopic.php?f=53&t=852

viewtopic.php?f=52&t=399

viewtopic.php?f=52&t=90

BTW I purchased a 383 SBC a guy built that would not start, dirt cheap because a compression check showed even newly assembled it only had 50-60psi compression, I took it apart and found the guy had installed the cam/crank gear assemble using the wrong combo of index marks and it required replacing two valves and the timing set and buffing out nicks in all the pistons but at the price it was still a good deal
 
Last edited by a moderator:
grumpyvette said:
.060 off the deck IS HUGE
Click to expand...

That's what I thought. It sure sounded a lot to me. The Block was a pretty original standard bore to start with. I'm wondering why someone would Deck it that much. What could be the possible reason one would cut it that much, other than a mistake?

Also appreicate the additional info that you provided.

Bill
 
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