Rebuild Machine Work (bore or not?)

Brian Chain

Registered User
So I'm about two months into a complete rebuild of my 93 sc - first time I've ever been into a car this deep. I just took the block, crank, and cam down to the shop. They are going to grind the crank, put new cam bearings on, and clean up/deck the block.

The area I am a little gray on is whether or not to have it bored over. The bores look to be in pretty good shape. The pistons popped right out the top (barely any ridge at all), and you can still see the crosshatch at the bottom. The guys at the shop noticed a few scratches on one cylinder wall, but otherwise said they looked pretty good. This engine only has 84k on it. I've also read several posts on here that indicate that it is better not to bore over until really needed. This will not be a race engine, just modded with bolt-ons. Total Seal rings are in the works if it matters.

That said, the guys at the shop had all kinds of horror stories about rings not seating properly, or not working somehow, due to the scratches. So now I have to wonder, to bore or not to bore? What would you do?

Thanks, Brian
 
If the crank needs to be turned more then .010 you might want to look into a good used one. The machine shop should be the ones telling you if it needs to be bored or not. They can use a bore gauge and check tapper and roundness of the bore. No matter what it will need to be honed to seat new rings. When rebuilding the motor use only WD-40 on the rings and cylinder walls, that will get the rings to seat quickly. There can be no motor oil or grease on the cylinder walls or piston.
 
Brian Chain said:
(barely any ridge at all)

That right there says the bore is worn to an extent. The question then becomes not "IF" it should be overbored, but rather "How Much?"

There are specifications for cylinder diameter, taper (wider at top than bottom), concentricity (egg-shaped), and clearance between piston and bore. Generally considered, the further you get away from spec results in less durability and less power. If you're after OEM durability, or better, then IMO an overbore is just about required. If you're just wanting something for now and plan on another engine later then perhaps you could get away with a re-honing.

If you choose to overbore be sure to tell them you want it honed with deck plates.
 
If you're going with stock piston replacements, Sealed Power has them in various overbores. .50mm, .75mm, 1.0mm

The shop may be able to go with the smallest overbore and keep everything happy. I'd make sure you get the skirt coated versions of the pistons (I think that's all that's in the pipe these days) and I would think the shop would like them in hand before doing the work.

If you do replace the pistons, and work the rods, re-balancing the reciprocating mass would be a good idea.
 
Well the shop took a closer look and they definitely recommend 30 over. So along with your comments I suppose I have good reasons to want the overbore. They will order up Sterling (sp?) pistons, they are oversized stock replacements. They want about $160 for the set, which I've read is a good price. I don't know if they are skirt coated, will check that soon. Anybody have experience with these?

Unfortunately the shop doesn't have a 232 torque plate (neither does anyone in town, apparently - it's a long way to the next major town that might have one). I was planning on seeing if they could rent one. Guess I read on here somewhere that somebody has one they will lend (rent?) out too. Anybody know who to get with on that?

I will ask also about rebalancing. My harmonic balancer is in great shape so I wasn't going to buy the aftermarket one that everybody likes (pretty spendy anyhow). They know not to turn the rear main surface on the crank, and to limit the rest to .01.

Mike, what work would I have done to the rods? Aren't they already shot-peened? I know the new pistons need to be installed, but there is apparently something else?

If I'm going to get it done I want it done right. Thanks for the help so far guys.
 
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Parker, why does very little ridge mean that there is more wear? I thought it would be like a brake drum, where more wear meant more ridge?
 
Its not just the ridge at the top, the cylinder does not wear round. So you'r cylinders could have a large tapper to them or just really out of round causing the need to bore .030 to make them true again. .030 overbore will give a slight performance increase since you will gain a very small increase in displacment but more importanty you will unshroud the valves helping head flow.
 
you dont need a torque plate, dont believe the hype, if you dont rev the piss out of your car you dont need it to be balanced, stock replacement pistons rarely ever throw the balance off that much to make a difference. Only thing i would do is worry about the crank, if they are 100% sure it cant be polished up. Other than that its just another 3.8<--similar to whatever maching any 5.0L would need etc, nothing special
 
I would go ahead and have it bored out just to clean and straighten the cylinder out. Remember its been from hot to cold for many years of different types of weather. The rings themselves overtime create quite a piston to wall clearence. I just had my motor machined and the piston to wall was about .016".

Total Seal's are great because it reduces pressure in the crank case and only has a max of 2% leak. However, seating of the rings is determined by the hone, type of oil, and break in procedure you use. The total seal ring isn't real stiff so it's easy to break in.

Right now I'm .020 over with total seals. I just got my tranny back so i'm puttin everything together this weekend hopefully.
 
Stock rods are forged (as are most rods in any car today) and have a line where the two parts of the dies came together. The angles created by the parting line can create stress risers ini the steel along the path of the line. Polishing the beam takes that parting line out and aligns the grain of the steel.

Shot peaning is done to improve the surface density of the steel making it more resistant to cracking. Stock isn't shot peaned as far as I'm aware.

i'd ask for some research on those pistons. never heard of them, though searches tell me they may be an arm of Federal Mogul. Make sure you get skirt coated pistons. shouldn't cost anything more and they are most likely just Sealed Power pistons. They make the only stock replacement hyper piston I'm aware of and the price sounds the same. Last I checked the no coated, and the skirt coated versions were the same price.
 
Well, am still talking with the shop (I suppose I shouldn't expect this to be a quick process) and they think it is very possible I can get away with only polishing the crank, not grinding (thanks for the suggestion assclown). Also am not planning on balancing. However, sounds like I will have the block bored with plates, just for kicks.

Mike, that makes sense on the rods. I guess I had seen some articles on turbocharged sn95 v6 mustangs. One of the mods that seemd to show up was SC rods...that's where I read that they were shot-peened. Could be that the process was done after the factory though, although I don't know why the stang'ers would want to use them if that was the case?

Also, the pistons that Sterling is putting out now likely have coated skirts, according to the shop. I will try to post on here if I find out who actually makes them. At summit racing they list Sterling/Federal Mogul pistons as part of the same line so maybe that is true. Is there any way to visually tell if they have coated skirts once they are delivered?

For those of you with Total Seal rings, can you share a little info? What prep needs to be done to the rings/cylinder walls to get these to install properly? I have a ring compressor but have read that the shop may have to put the total seal type on for me? Anybody have a good description of this process? I've read about stones (of a certain grit?) used to prep these as well - what should I worry about with that? Basically, can a know-nothing like me get these installed correctly? Or should I stick with the stock stuff?

Am jumping the gun slightly as I haven't done much searching on the forums about rings, so I apologize if it should be obvious. I'm trying to look into them more...

Thanks again, Brian
 
Sterlings a good make, coated pistons have a gray paint on the skirts, stock rods are decent till like 400hp, no need to prep them, if you do want to strenghten them a little (waste of time) buy a performance book, they'll list step by step how to do it. You bascially as mentioned earlier grind down the line (casting line) that runs down the middle of the rods and have them wheel abrated/shot peened whatever(there is a certain speed and size of particle which works best to strengthen), you have to CAREFULLY wrap all machined surfaces of the rod <---shot peening is a waste of time if you arent running a huge blower, or nitrous etc, your cast pistons will blow a ring land well before this if it detonates. just buy regular moly rings. If you are building a race engine buy all race parts, if you arent, leave it stock, first upgrade on my list would be forged pistons and a balance if you are going to be getting into some serious hp.
 
Any good ring is going to be file to fit. You would need a ring filer to get the right ring gaps. Don't waste you'r time grinding the rods if you want more strenght from the rods the best thing you can do is ARP rod bolts. I think they are around $60.00 for a set. If this machine shop dosen't know what plateau to put on the cylinder walls and they don't want to look it up themselfs then take you'r block and run. But if you must know Moly-face or Cast top ring 280-320 grit finish hone 22-24 degree cross-hatch pattern off horizontal axis. But most good shops like Coy Miller have there own technique that they have proven to use.
 
"If you are building a race engine buy all race parts, if you arent, leave it stock."

Yeah these are basically my thoughts too. I'm trying not to go all out on this but the total seals seem like a good design improvement. Am leaning toward stock rings at this point though to avoid complications.

BKB, thanks for the info. I actually am impressed so far with this shop - I will make sure just in case though that they know how I want the block finished.

So you can't (or it isn't common practice) to re-use the rod bolts? If this is true I'll plan on buying those ARP ones, I can get my head studs at the same time. Should I re-use the main bolts?

I guess I don't know this: when the block is prepped, and I have the new pistons on the old rods, etc, can I put it all back together? Or do I need them to put the rotating assembly in the block and torque down the mains (especially if they need to verify clearances)?

Thanks, Brian
 
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This is what the sealed power skirt coating looks like on a piston.

piston_two_heads.jpg


In general I'd take the suggestions of your machninst. he's the one that's going to be asked to stand behind the motor. Stock rods are proven good for up to 400rwhp by folks actually doing that. Most folks making over 400rwhp (other than XR7 Dave) have already gone with new forged pistons and different rods so not much experience has been had with that.

If you're planning on racing regularly, I'd do the extra work on the rods but otherwise I suppose it could be a waste.
 
If its 89-93 they are pressed pins and the machine shop must press the new pins into the pistons and rods. If its 94-95 it has floating pistons and you can install the spirox rings you'r self. The head bolts are the only TTY bolts in the motor so they are the only ones that MUST be replaced. It is suggest that the rods should be resized if you install rod bolts, i never have.
 
If the pistons are from federal-Mogul and the same as what Sealed-Power provides, the pistons will come with new pins and pin locks to support full floating design.

I talked with Federal-Mogul's tech line about the pistons since the part number is the same 89 thru 95 and that's what I was told.
 
Mike8675309 said:
If the pistons are from federal-Mogul and the same as what Sealed-Power provides, the pistons will come with new pins and pin locks to support full floating design.

I talked with Federal-Mogul's tech line about the pistons since the part number is the same 89 thru 95 and that's what I was told.

Yes, those pistons will work on both pressed and full floating but the rod is what determans what you use. Since the 89-93 rods are pressed fit you would still press the pins, 94-95 have a bushinged end for full floating so you could install them yourself.
 
Thanks for the info guys. A picture is worth a thousand words.

As an update on the project, it has been bored 30 over, Sterling pistons and moly rings are on their way. Looks like I got away with just polishing the crank, and got new cam bearings put on. Also had the block decked for MLS head gaskets. All that is left is getting Clevite bearings ordered and bringing in my rods for the new piston install, since they are 93 rods.

Well, that and milling the heads, valve job, buying gaskets and head studs, and let's not forget all the work to put it back together and back in the car.

Thanks again, Brian
 
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