valve spring, sticking valve?

[jaredts]

Well, I was going to wait and run a few errands with the truck, but I think I'm going to tear into it tonight.  Been several years since I pulled heads, but I think I've got it down.  I want to check out the bores before I buy anything.  Currently torn between vortec and the summit heads, which I have read are dart s/s castings.  One thing I'm a little concerned about with the vortec option is compression ratio.  With an old tired bottom end I'd hate to tax it too hard with a big jump in compression, but I'm still considering it.  Who knows, maybe my truck won't look or run like a jalopy in the next few months.

[big bear]

either route will help ya out.. good luck man

[jaredts]

A few hours work and.....
cracked exhaust valve:


headless:


The cracked valve was sunk pretty deep in its seat compared to the others, but I think they'll all be pretty ugly.  Haven't taken the other head off yet, but I'll get it.

[jaredts]

I ordered the Summit heads today.  Borrowed a telescoping gage to check the bores hopefully tonight.  Threw calipers just on the ridge and got 3.99", so I'm pretty sure they're stock bore size.  Checking bores from the top, should I just check them in two directions 1/2" down or so, and then bring that piston to the bottom and check it both ways at the bottom?  Anything with the heads off that can be done to evaluate rings?  It would be nice to have a dummy plate that I could bolt on in place of the heads and leakdown test it.  Should I just wait for the new heads, bolt them on and leakdown test every cylinder before putting everything back together?

[VileZambonie]

You're going this far why not do it up? This kit with pistons is right around $200 bucks http://www.summitracing.com/parts/SUM-SBCKIT1-000/?rtype=10

[beastie_3]

usually pistons with an oversize bore have them stamped on top, so if there is no stamp, then pretty sure its standard bore, which seconds your measurements.

[1979C20]

Those are stock pistons. Id know, i have them. You have a cracked valve, i have a cracked head. And strangely enough, my pistons are in the same position as yours....

[jaredts]

The cylinders look like its got some miles on it, but no score marks and the size checks good everywhere I checked.  I'm willing to take a little risk as I didn't want to pull this motor at my house, I need to take it somewhere else if I'm going that far (no garage, no hoist, no stand).  If I could do the bottom end with the block in the truck I'd go for it.  I saw your post, '79c20, and it is kinda funny.  Your symptoms were pretty close to mine.  I halfway expected to have air coming out an adjacent cylinder when I did my leakdown test after seeing your post.  My best price for rebuilding my heads was $450, so I just spent $630 on new, better heads (shipping included).

[jaredts]

Just clicked on the link, Vile.  Out of curiosity why would you buy a kit with new 4.0" pistons if the old ones aren't damaged?  If you are only honing the cylinders wouldn't you just rering with the old pistons?

[jaredts]

Heads just delivered, less than 24 hours after I ordered them!  Shipped out of Ohio, which isn't far from my house.

[VileZambonie]

Because they're hypereutectic and flat tops. Yours are dished cast pistons. Why wouldn't you replace them? To save $80 bucks having them hung on the rods? I'd definitely go that route.

[jaredts]

That makes sense.  I really wish I had the place to pull the engine and go through it.  It almost looks like there's room to hone it right where it sits.

[VileZambonie]

Where there's a will there's a way 

[jaredts]

I played it out in my head, and although it might be possible to rering in the truck certain steps don't sound like fun, and I'm not sure I could get a hone in the back two cylinders.  I think I'll put this together and probably won't be 100% pleased with it.  It smoked a little before, and even though I didn't detect anything with the bottom end during the leakdown test i'd say It'll still smoke a little--I have a hard time believing it was valve guides/seals.  So the plan is to put this together and find a buildable block for a long term solution.  Got the new heads painted, the block deck scraped and cleaned and all the bolt holes tapped.  Wipe it down one more time tonight and bolt the heads down (unless I have to work late).

[1979C20]

I beat you to the punch! Got to drive my truck last night.
http://boxwrench.net/specs/chevy_sb.htm
this page is very helpful when rebuilding the top end. Make sure you torque your heads in the special sequence. And i torqued them to 30, 50, then the required 65 in the special order. You can even view my page for help if you need it.
http://forum.73-87chevytrucks.com/smforum/index.php?topic=20691.30
good luck!