This is the max for factory tolorances and is also what I will likely end up with. Its a .040 over block that was a generic remanned engine.... the holes are now at 4.0425 and the machinist said that pistons are normally .001 small. Will this be okay with hypers?

 

is it a 350 or 305? cheap as blocks are you might want to look for a builder. i wouldn't want to go to +.060 on a block, even if people do it every day.

 

Its a 350 factory roller block. I'm with you on the .060 over stuff too. The bores are round and have been deglazed with a stone. I could have him take another .001 out of it and run forged I guess but I really don't want to. Are there any piston manufacturers that don't make the pistons .001 small?

 

i thought everyone made their pistons to spec, or the same size and allowing for expansion and the holes were all the same with the pistons differant based on what the were or what they were used for.

 

Piston clearance is built into piston rather than cyl wall. For example, If you have a 4.030 bore and the piston manufacturer calls for .0015minimum clearance, the piston size will be 4.0285. The number to be aware of is the Max clearance. if you have the same piston and it has a MAX clearance of .0035 then the piston will work in a bore up to 4.032. These numbers were used for example purposes but you get the idea.

 

A good machinist mics the piston then hones the block to the right size. I wont hone a block with out a piston in hand.

With hyper pistons I usually leave .002" and yes they usally come in around .001"under so ill go .001" over (like 4.041") or whatever ever to get my clearence.

You should be able to get by though if you need to use that block. id redo it and go to 60 over. ive never had anyone have a problem.

 

After sonic testing the block, I imagine?

I know the older blocks goto .060 just fine. I dunno about the newer blocks..

-- Joe

 

Generic reman engines are something I've tried once and will never do again.
I've been referring to them lately as "sweatshop engines". In many cases the tweakers who build those engines do not care about how long your engine lasts in any way shape or form, as long as you don't bring it back to them before the warranty is void. They don't get paid enough to care.
Here's a list of the things that were wrong with the first and last one I'll ever buy.
Grit in block, lots of it, very poorly cleaned.
Lifter bores not honed. Scuffed cam within 20 min run time.
I tore the engine down and found more.
Timing chain was rubbing against the block, putting iron chips into the oil scuffing the bearings and scoring the piston skirts.
Upon reassembly, I found that several of the rod bolts were stretched, they simply yeilded before the torque spec was reached.
There was more too.
The bores weren't torque plate honed, and between each bolt hole in each cyl was a shiny spot where the crosshatch was completely obliterated.
The engine was simply a waste.
Doing searches, I've found other stories of guys who bought a rebuild and got 15,000mi out of it.
Take your chances if you want, but at the very least it would be to your advantage to clean it yourself, completely.
I ended up cleaning and I am presently repairing mine, for a cost of which I could have built a proper engine.
When it's finally running it will be my spare engine.

I've done ring jobs on engines that had more than .0035" skirt clearance and they held together for years. But my suggestion in your case is to tear it down and remove the cam bearings and clean the entire block. Then reassemble it for the least possible cash outlay in parts. And call it practice, for when you do a proper rebuild. Just run it while you're building another.

"Burn An Learn"

 

It is torn down with the block, crank and rods at the machine shop right now. The long time machinist just happens to be a long time freind and was letting me know that I will most likely end up with about .0035 clearance. He will mic the pistons and said if any were smaller than 4.039 he will send the set back, I guess he's done that in the past. I agree with you on the sweatshop engines and would never buy one myself, I just pulled this one out of an IROC that someone had replaced the original with. Whatever remanufacturer it was that did the rebuild converted it to 4-bolt mains . I don't know why because it had a peanut roller cam and friggen swirl ports in/on it. Anyway, I was pulling the main caps off and one came off in two peices , it was cracked right down the middle broken in two. I could'nt tell though untill I pulled it off. It's weird that the engine never made any noise or came apart or somthing, I flogged it regularly. I guess the peanut cam/swirl ports/TPI saved it.

 

problem with trying to measure a piston is they're tapered and you don't have a good datum point to measure from. i've also never subscribed to the belief that a block is fit to the piston, but rather the other way around. called around once and it seems about 50/50 on how shops approach doing things.

 

Hmm, I don't know. I trust the machinest, he's been doing this everyday for about eight years. They do a lot of exotic stuff too, high dollar tractor pull/drag race engines, rare #'s matching stuff, and have a good reputation too.

 

Converting an engine from 2 bolt to 4 bolt is expensive, and fairly difficult. Are the caps splayed?
Maybe the job was done incorrectly and that's the reason for the broken cap.

 

No there not splayed, there straight down just like a factory 4 bolt cap but the bottom side is not all on one plain. The others seemed to fit all right?

 

Do they look like factory caps?

 

Sorry, double post....

 

You CAN'T fit pistons to the block.... the only adjustable part is the hole in the block. The cylinder is adjusted to fit the piston.
Not the other way around.

How would one go about sizing a piston?
Must be one of those NEW tools... a Pistonator....

Typically the cylinders are bored then honed to fit a particular piston.
A good engine builder will 'fit' each piston to a particular cylinder because the piston tolerances vary a little bit.
The adjustment is done via honing the cylinder until the desired clearance is achieved.
So, each CYLINDER is fitted to a particular piston.

While you're in this area you may as well plan on setting the ring end gaps properly. THIS time the ring IS fitted to a particular cylinder.

 

But a better engine builder will call the mfg, and ask what the recommended bore is after final hone.

Piston manufacturers machine their pistons to various tolerences because they have different expansion rates. A high silicoln alloy piston will be larger than a normal forged piston because it expands less. If you try to hone the block leaving your favorite "clearance" the piston will forever rock in the bore.

Some people overthink things, when simple phone calls will provide all the correct answers they need.

While the sarcasm in your post was kinda funny, you still don't fully understand how it works.

-- Joe

 

Expensive? About $250 for labor, plus the cost of the caps. Straight caps are way easier to do than splayed.

Bolt the inner bolts, drill and tap the new holes. Torque to specs, then align bore it. Replacement caps come waaaaaaaaay undersize, so you bore the cap to match the rest of the hole.

Its about an hour to set the caps up, drill and tap them correctly. Another hour to align bore and hone them.

-- Joe

 

Oh... Now I see
So they're the aftermarket 4bolt caps, and they don't need to have the saddle machined to fit.
You might be able to get a factory cap to replace that and just have it align bored and honed.
Well... You still gotta wonder what happened to bust it.
Nuther thing on the list

 

Detonation is what breaks caps. Usually one breaks and you never notice until you teardown the motor. Thats why you should mag your caps during rebuild.

If he gets 1 replacement steel cap, he can align bore and hone it to match the rest. They come way undersize, as I said before.


-- Joe

 

I like it when I learn something new... Thanks

To me $250 + parts is expensive tho.

 

I'm actaully going back with 2-bolt caps and studs. The shop had a couple three hundred of them to go through and he found some that will fit with just an align honing. I'm going to put bolts in the other holes and grind off the heads. After some more searching I see that you can set up most hypereutectics with as much as .0045 clearance. So I'm just gonna go that route.

 

Hypers don't really expand at all, if i recall. I have never used them, but have done plenty of reading. I'm a fan of TRW and JE/SRP forged pistons.

Good luck with the motor!

-- Joe

 

I always have my pistons in hand and have the block honed to what I have. Thats the way to do it if you are being picky about the build. Calling the manufacturer and getting a book spec will build you a book motor. When you start checking things like pushrod length, cam timing, valve height, spring pressure, ring gap, and various other clearances that arent checked on a sweatshop rebuild, you dont just hone the block to 4.030 and throw the pistons in unless you just dont care.

Detonation will ruin a piston or valve much faster than anything else. Something about melted ring lands or melted valves.

 

True, thats how mine eventually blew up, but a lot of folks crack the main caps under detonation, or worse, preignition.

-- Joe

 

Something doesn;t jive here.
If you're going to go the the trouble to repair the broken main cap, Y fudge with the bores? .060" over is no problem.

The line bore on the main saddles is much more important of an issue on this build. .0035" piston to wall clearance is ok with Hi perf hyperteutectics like KB's.
They are actually very tolerant on bore size. FM H345NP's will tolerate this lil extra clearance as well. Its the OEM factory cast non hypereutectic pistons that can't tolerate a loose fit. They'll make noise.

But I'd bore it .060" over and not worry about it.

 

The trouble with some overbores is finding pistons. (not in general, but in the specs you want).

When My motor blew up, I had to bore it .040 over. Theres not many .040 blower pistons. Infact, I only found one.

-- Joe

 

Well, as said earlier the machinest is a good freind of mine, I've known him since the 4th grade or about 18 years......... So he's doing this on the side to help me out, I just don't feel comfortable with .060 over, it has nothing to do with saving money as it would'nt cost any more to do. And after reading most of the manufacturers specs for max tolorances I see that they can be set up as loose as .0045, so I don't feel like I'm fudging too bad. It's not like I drive the car daily and need 100,000 plus high performance miles out of it. That would probably take me twenty years to accumulate and I plan on going bigger before then. Anyway, the block is decked, honed and aligned honed. the rods are resized with new bolts and I had to get another crank to go .010 under ( the one that came out of the engine was .020 under and needed turned ). So I'll be picking it up after the pistons come in and soon after ridding the vert of the 157,xxx mile old LB9 :rockon:

 

You can make all the calls you want.
Get the mfg.spec thousand times.
THAT WILL NOT make the pistons fit correctly.

In the final 'round' your machinest WILL hone EACH cylinder to a SPECIFIC piston.
He will set the skirt clearance to the mfg. specification.
That's IF you want a precision engine.

He can fudge a little either way.....'most' machine shops don't measure out to past the 4th decimal place anyway.
I doubt any except the most fastidious speed shops will hone to a specific ten thoudandth tolerance... it takes wayyy to much time and effort and you reach the point of diminishing returns very quickly setting up a street engine that closely.

Actually the skirt clearance is not 'real' critical...
it's just a matter of having enough to keep the piston from galling in the bore and not having too much so the piston rocks in the bore excessively.

You'll need to be looking at ring end gaps while you're working in this area, also.
Have the ring 'back clearance' checked and the ring to land clearance checked.
You 'may' want to consider a set of 'file to fit' rings so you can set the gaps to the spec. you want them to be.

There's a WHOLE LOT of measuring to do if you want a truly precise engine.

A 'blueprinted' engine may be way off on the bad side of factory specifications and still be considered 'blueprinted'.
It's a thing called 'tolerance stack'.
Blueprinted. That's such an overused term anyway and most folks don't really know what it means.

A street engine will run MANY thousands of miles with clerances anywhere inside the factory specs. or mfg. specs for their respective parts.

 

I'm bringing this thread back just to warn anyone who may be reading it and considering buying a sweatshop engine. ie: autozone, orielly's, aarons auto or whatever you have in your area. DO NOT DO IT! After getting everything back and bs-ing with the machinist, heres what he found: the main bore was way out off line, odd considering it was converted to 4-bolt caps, the decks were milled flat but one corner of one deck did not get cut as much leaving a huge high spot. If you couple stuff like this with assembling an engine with an air ratchet, well you get the idea. Man am I glad I decided to tear this thing down, I was just gonna stick a zz4 cam in it, bolt on a set of afr's and drop it in.

 

I'm with you on that one.
I've been trying to undo the damage that was done on this one for the past several mos.
I was glad I fired mine up on a test stand, cause it would have started clattering after 500 mi.