.005 Ridge at the top of the cylinder wall...problem?

If you can feel a lip, bore it. It might work if you hone it and re-ring it. But thats the rule of thumb I go by.

Good Luck

Gary

 

Total cylinder taper needs to be .007 or less. That's for a "grandma-mobile". Low RPM, not too many miles, etc. and it sounds like that's just what this engine's intended use will be.

If you really do have a .005 ridge, you have .005 on each side of the cylinder; or .010 total. You can look forward to a short service life, and perhaps some oil-burning as well.

HOW was this ridge measured? .005 is not very much. The last time I thought I had a small ridge like that--the machinist measured it and determined it was twice what I thought it was.

Keep in mind that the ridge is the result of the old rings scraping against the cylinder wall; and the old rings will also be worn by the cylinder wall. If the new, unworn rings contact the ridge, they'll be beaten to death by that ridge. At minimum, you'll have to "ridge ream" the cylinder.

Sorry, guy. That block really should be bored.

 

I would take bore measurements at various locations in each cylinder like 1/2" down from top, middle, and bottom measuring from intake to exhaust then take a couple side to side and see where you are and/or how much variation there is. If you have a .005 ridge theres at least .010 wear on the diameter but it could be more on certain cylinders. Once you have more data you or an experienced rebuilder can make a more educated decision. I record the dimensions for each cylinder on a spreadsheet so they can be compared easily.

Generally speaking, if measurements are fairly consistent without too much egg shape and don't exceed .010 on the diameter you could get away without boring considering the intended very light use. Your manual may give limits on cylinder wear so check that if you haven't already. I'm probably in a minority because the common approach is to bore it no matter what which starts a chain reaction of more money. The worst that would happen is maybe a small bit more oil consumption and maybe a tad lower compression neither of which you may ever notice in that car.

I have rebuilt 2 engines on daily drivers (not nailheads) out of necessity when I was poor as a church mouse with more of the ridge than that. I used a hone on a drill, installed new cast iron rings on the original pistons, and didn't have any problems. I drove both of these vehicles everyday at least 2 years afterwards. Sold one to a friend and he drove the heck out of it for naother 2 years with no issues. I was quite surprised how well going cheap worked worked in these cases.

Having said that, knowing the level of work you are doing on everything else, a couple years from now you might regret not truing up the cylinders for a fresh start. You might have what, maybe $600 in boring and new pistons. It all depends on your budget I guess.

 

The ridge at the top is carbon, use a ridge reamer to remove it. Let proper measurements dictate if boring will be required.

 

If you are doing a ''overhaul'' and not a ''rebuild'' ,,, just cut the ridge out of the cyls and go on with the hone job.... I have done a lot of these engines that way and never had a problem...the reason that you cut the ridge is to prevent the new rings from bumping them and breaking the ring lands out of the pistons when the engine heats up.... just make sure the other specs of the engine are correct.. pay close attn to the ring end gaps.... and clean the ring grooves real good....look the pistons over real good for cracks.... far and away, the main thing that I have seen take out a nailhead has been a factory piston busting and wipeing out the rest of the engine.... if there is any doubt about a piston , replace it....

 

For the most part, I go along with JasonZ and Doc. Do the careful measurement bit first, then if conditions permit, ream the ridge, and hone the cylinders. If you are going to go so far as to replace the pistons, it would be silly not to replace the rod bearings. If you are replacing the rod bearings, it makes sense while you have it apart to replace the mains. Replacing bearings? Better check the crank for wear and taper. You will need a chain and gears for sure. Do you see where I'm going with this? If it's more then a hone job and replacing the rings, I would bite the bullet and do the whole thing. A chain is only as strong as it's weakest link.

 

Here you go

http://www.egge.com/site/?d=48&dt=1&SubCategoryId=2&make=BUICK&rpp=10&pageCursor=3

Or here is another option - I've been using falcobglobal and so far really like them. All quality parts.
http://cgi.ebay.com/ebaymotors/Buic...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

 

Yeah, Buick spec is 0.008" max before a rebore is required.

Like Jason said, Falcon Global does have Nailhead parts at great prices.

Another supplier is Russ Martin. He's the west-coast Nailhead guru. See his website here:
http://www.centervilleautorepair.com/
He posted on the Yahoo board that he has $250 piston sets and nicer ones for $325 or so.

 

When was the last time anyone has heard of piston knurling? I used to hear of it some time ago, but haven't for a long time. The one particular ocassion I really remember was where the cylinders were cleaned up with a small bore, the pistons were knurled, some teflon buttons were put in the skirts of the pistons so they weren't too undersized, and oversized rings were used to seal the pistons to the cylinder walls.

?????

 

About as durable as valve guide knurling; I'm glad it's not done anymore!

Devon

 

Basicly it is a stop gap measure to make a worn out piston fit the cyl... it was used back in ww2 when parts were hard to come by....