sbc engine rebuild help

Hi guys I'm attempting my first rebuild and have been looking for some good guidence. It seems like a lot of you guys on this forum are pretty sharp when it comes to rebuilding so I signed on up.

I have a 91 305 Roller block in pretty good shape from what I can tell so far. It had 130k on it but had low compression on one side (1357). That side had an average of 100 psi and the other (2468) had an average of 200 psi. I tore down the entire block for inspection and here's what I've found. The side (2468) had what looks like a rebuilt head. Probably had something to do with the higher compression. But the ring gaps are all about the same, .032 . I checked the cylinders with a bore gauge and the worst one had a .002 difference in it. That's my first question, is that one good enough to still do a hone job on? The cylinders look good I can even see the cross hatch in them. Oh and it has had a crank job done because there are over sized bearings in it (.013) (is that a weird size?) and they look really good and the crank journals look good too. Must of been done right before I got it. Another thing I noticed was all the ring gaps weren't staggered, they were right up and down from each other. That's not right is it? Also I have a 350 and the worst one in that block is .007 tapper. That one probably needs bored for sure right?
Any help is much appreciated.

Joseph  

Hi there,
 You bore all the cylinders in the block the same at all times.
 Save yourself a lot of questions by buying Mr. Vizards book and
 the heads should be matched by way of equal cc capacity and valve
 placement. Read a lot and THEN ask the Experts. Do not presume...
   Take your time and double check every thing.. Thorough cleansing
 is a must. Use lots of oil in the assembly..All very basic and all
 very necessary..Do it right and only do it once and be a winner..
  All the best from Skyeking....  
skyeking

Wow. Go buy a book. Thanks. I have bought a couple books but they weren't really that great that's why I came here. I guess I need to buy some more. Thanks for everybodies help.  

The compression difference sounds like someone put a head with smaller combustion chambers on one side. Check www.mortec.com for the casting numbers on the heads, you will probably find 64cc's on one head and 74cc on the other. As for the cylinder taper, I'd have a machine shop check the block and get their recommendation since it will have to go there anyway if it needs to be bored. Most shops will tell you if you don't need boring and can get away with a hone job and new rings. good luck  

Hi there,
I would not recommend using a block with a cylinder
that has .007" slop in the bore. How long do you
intend to keep this motor?.If you do rebuild this
motor with bores like that I would go for the lowest
practicle compression available. Forget about long term
good performance after 10,000 miles. If you HAVE to patch
the motor up then do it. If you can wait and do it properly
all the better..Let the Economics decide...Skyeking  
skyeking

lol  

Does anyone know what a safe tapper to just do a hone job would be?  

if the cylinder is within specs then the taper would be too. Use a dialbore gauge and measure the cylinder in 4 spots from top to bottom and note them. Next is to do the other cylinders. Let us know what numbers you come up with  

All the cylinders had .001 or less except for the one that had a spot with almost .002  

Thats acceptable on the taper.  

Thanks. What kind of oil should I use to hone with?  

No thier the same heads. But I'm wondering if the rebuilt one has been shaved and may be that increased the compression on that side. I was also looking at the head gasket from the low side and it looks like it was cooked. Who knows. I'm gonna have to check the cc before I use them again.

Since I'm on the subject of these junk heads (187's) as most people call them, what would happen if I grind those swirl ramps out of them. Would that make them flow better. I've read up on people getting better flow from porting and polishing them, but never heard of anyone removing the swirl ramps completely.  

10w oil is good for honing if you can find some. The one head would have to be shaved alot to make a noticable difference in compression. I ground out the swirl ramp on a few cracked heads just to see if it was possible without breaking thru into the waterjacket and everyone I've done has broke thru. My suggestion is to leave the ramp alone  

Thanks for the heads up on those heads. lol.

But really thanks for the help.  

any time joe