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-   -   406 engine questions. (http://www.hotrodders.com/forum/406-engine-questions-226140.html)

95chevy406 11-15-2012 08:21 PM

406 engine questions.
 
Just bought a fresh 406(so i thought)
Ok the casting numbers says its q 4 bolt but it has 2 bolt caps.is this good?
Also has new h400p cp30 pistons.well it has a small rap(sounds like a wrist pin)
And i saw that they also ground the piston skirts to clear the crank.whats going on with this motor?

vinniekq2 11-15-2012 08:26 PM

poor match of parts and not put together correctly. pull it down,dont bandage a big disaster

techinspector1 11-15-2012 08:27 PM

Quote:

Originally Posted by 95chevy406 (Post 1611772)
Just bought a fresh 406(so i thought)
Ok the casting numbers says its q 4 bolt but it has 2 bolt caps.is this good?
Also has new h400p cp30 pistons.well it has a small rap(sounds like a wrist pin)
And i saw that they also ground the piston skirts to clear the crank.whats going on with this motor?

As a young man, I used to buy complete motors until I learned that every seller is a liar. Never again. I want it used up and ready for a rebuild or in pieces. Either one is fine, because the cost is commensurate with the value of the hunk(s).
Your noise could be anything, from a skirt hitting a counterweight to a cracked piston to a loose pin to a counterweight hitting the end of the dipstick to one of the rods hitting the cam to................:mad:

95chevy406 11-15-2012 08:39 PM

The guy said it ran good with no noises.the pistons only had very litle cabone on them.guessing less then 30 min run time.is it good to use 2 bolt caps on a 4 bolt block.the sound was coming from the # 1 or 2 piston.my cam is only a .435 .465 lift.

cobalt327 11-15-2012 08:41 PM

Are you saying the block is drilled for 4 bolts but now has 2 bolt caps? If that's the deal the caps won't be registered in the block recesses the way they should be. This would leave them largely unsupported and I would think this would be an invitation to have the caps moving laterally, aka cap walk.

techinspector1 11-15-2012 08:48 PM

Quote:

Originally Posted by 95chevy406 (Post 1611784)
The guy said it ran good with no noises.the pistons only had very litle cabone on them.guessing less then 30 min run time.is it good to use 2 bolt caps on a 4 bolt block.the sound was coming from the # 1 or 2 piston.my cam is only a .435 .465 lift.

What do you think the guy is gonna say when he's trying to extract money from your wallet??????? He's gonna lie through his teeth. TRUST NOBODY.
When the 400 blocks were produced, some were manufactured with 2-bolt mains and others were produced with 4-bolt mains. Of course the hot rodders immediately grabbed the 4-bolt blocks because they thought they would be stronger than the 2-bolt blocks. But hold on there, gasoline breath, it was discovered that the webbing in the 4-bolt blocks was not sufficient to prevent pulling the whole shebang out of the crankcase and runnin' over the crank. Oddly, the 2-bolt blocks were stronger and have been used ever since as the block of choice when building a 400. If your block is an original 4-bolt block and has been built using 2-bolt caps, it's still a 4-bolt block with weak webbing above the crank.

95chevy406 11-15-2012 08:54 PM

Never took the cqps off to see if it is a 4 bolt but the casting number says it is and yes it has 2 bolt caps.
3951511=70-73 sbc 400 4 bolt main b&g body

cobalt327 11-15-2012 09:16 PM

Quote:

Originally Posted by cobalt327 (Post 1611785)
Are you saying the block is drilled for 4 bolts but now has 2 bolt caps? If that's the deal the caps won't be registered in the block recesses the way they should be. This would leave them largely unsupported and I would think this would be an invitation to have the caps moving laterally, aka cap walk.

Having said that, I cannot remember if the 2 bolt caps are as wide as 4 bolt caps. Too late to go out to the shop to look right now.

1Gary 11-15-2012 09:31 PM

Techinspector1 is right about resellers that are private sellers.There are plenty of honest shops building quality engines like ours that suffer from situations like yours. Those honest shops are nothing without you guys trust.We do really need that.

Just to I.D. what you have or don't have,it sounds like a total teardown.That would be my suggestion.

cdminter59 11-15-2012 09:42 PM

406 engine questions.
 
Mount the motor on an engine stand. Flip it over to remove the oil pan. Unbolt one of the main bearing caps to see if has 4 holes or two holes under the cap. If it has 4 holes find the guy who sold it to you and get your money back. Tell him you will take him to court if he doesn't want to give the money back.

95chevy406 11-16-2012 12:53 PM

Got it all torn down.it is a 2 bolt block.stock crank turned .010 on rods and mains.pistons and rods all look good and pins move freely..main bearings have alittle grooving and one rod bearing lock was ground off.the kotor also had low oil pressure at idle after warmed up.less then 5 psi.still not sure what the rapping noise was.

95chevy406 11-16-2012 04:39 PM

And on all the big ends of the rods there are little cross hairs like they were honed out so i think they were sized.im hoping it was either a bad bearing set or dry start up.

vinniekq2 11-16-2012 04:49 PM

measure all the parts while its apart,,balance?

95chevy406 11-16-2012 04:52 PM

Im gonna have the crank and rods checked.

cdminter59 11-16-2012 08:42 PM

Quote:

Originally Posted by 95chevy406 (Post 1611987)
Got it all torn down.it is a 2 bolt block.stock crank turned .010 on rods and mains.pistons and rods all look good and pins move freely..main bearings have alittle grooving and one rod bearing lock was ground off.the kotor also had low oil pressure at idle after warmed up.less then 5 psi.still not sure what the rapping noise was.

Check the rod that the bearing lock was wore off, look at the crank journal where that bearing fit also to see if it spun any. Like was said the crank and rods need to go to the machine shop to be measured.


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