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Discussion Starter #1
I've got my ztec apart for a "standard" rebuild. Does anyone know what the max cylinder bores can be to install new stock bore Pistons and rings?

I'm at 3.3395" and super consistent (barely .0001" out of round or from top to middle to bottom measured with a tri-tip bore mic that I grabbed from work). Nominal from the factory is 3.3386 (84.8mm), so I'm roughly .001" over new already.

It has a very slight amount of scoring on all cylinders on the intake side. I'm guessing I could clean it up with a cylinder hone fairly easily, but I'd likely add another .001 to the bore size...

So, will a bore that's a few thou over new (likely 84.85mm vs stock 84.80mm) work with new stock Pistons and rings?...

Thanks!
 

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Discussion Starter #3
I understand that, but before I take it to a shop and have them give it a .020" overbore, I was wondering what the bore tolerance was to still use stock Pistons...
 

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What you need is the shop manual tolerance numbers for wear.

Can't "Bore" it a couple thou., that would only be by honing it. Once you say bore, that is going to the first oversize piston/rings at least (.010 if avail.).

As a rule of thumb, anything more than a light ball hone job to freshen the cross hatching would mean time to go up a size.

"slight amount of scoring" sounds like time to bore to the next size, any lip at the top?
 

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Like said that last post. You can get away with up to .004" from wear and seen even .006" but the looser you get the more piston rattle and pistons being cast will tend to try to crack skirts the looser they get.

These engines start out with tight bores as compared to old school but they can run fine a little looser. I ran various engines with cast pistons at .002"-.003" all day long in hot rods and up to .008" using forged ones and bigger bores (4 inch+). Those numbers are real world piston to wall clearances, not any spec based on some theoretical bore size or book number. So, measure your pistons. The wear scores are from piston rocking at TDC on the major thrust side, why they put oil spit holes in rod/bearing, to try to stop some of that. Cold start mainly does it when pistons are loose and not heated fully to be round yet.

Any ring wear edge could potentially crack new rings/pistons as they will have tight lands and if one has rings a bit higher on piston from tolerance wandering then new ring may hit bottom of wear groove lip to crack ring.
 

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Discussion Starter #7
Pasta and Sailor, when I say "bore" I'm
Referring to the cylinder size, not performing a bore. Sorry, my wording wasn't clear.

Thanks amc. That's what I was looking for. Seems like I have about .005" piston to cylinder clearance (on diameter) right now. If the new Pistons measure the same I'd have .006" or so after I hone it (.003" per side).

I'll try and run the hone through it and see where I'm at, then make the call to take it in for a .020" overbore or not...

Thanks
 

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Where do you get that addition? .005" plus .003" on each side = .011".............and where did you get .005" after the OP up top said you were at .001"? You need a firm grasp on where you're at or you will be in break city faster than spit. Is this a race vehicle? (the 'DirtOvalBoy' thing)
 

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Old Phart
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Sounds like he's thinking of a .001" total straight hone job to clean it up, I'd bet that isn't possible.

Can't see it from here, that's why I asked if there was any perceptible ridge from wear.

Visible scrapes are the current question mark, can't see how bad. If they disappeared adequately with a ball honing and it measured OK (no ridge) it could be fine as is.

On the other hand, visible wear can often mean even a first oversize won't clean it up. The recheck mentioned before a decision makes sense.
 

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Discussion Starter #10
The Pistons I took out measure 3.335. If I hone a thou and a half out of the bore it will measure 3.341. That's a difference of .006" or .003" per side... I've never just tried to just hone a decent looking block, so I wasn't sure what the acceptable clearances would be...

I don't know if I'll be able to hone the bores clean to 3.341 but thought I'd try if .003 per side is acceptable for piston to bore clearance before I take it in to get punched over. The scratches aren't much more than visible (can barely feel them with my fingernail), and what little ridge there is at the top will hone out (only a few tenths on diameter).

Yes, it is a dirt oval racer! :grimacing:
 

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A ball hone will NOT work for that, it hones EVERYWHERE and not just at the tight spots. It is for deglazing ONLY, not straightening the cylinder.

Odds are very high that small an amount honed will in no way clean up the top ring wear 100%. Most visible scratching requires at least .005" to pick up all of it. Some (a lot) will go away at .003".

You don't have to get rid of all the wear but desirable. I've run plenty of engines really hard with slight amounts still there and they ran like bats out of you know.
 

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Discussion Starter #12
Thanks amc. I found the stock specs for the engine in here. I must have been sleeping the first time I searched. I started the thread because I couldn't find any specs for piston clearance. I should be between .0007" and .0015" piston to wall clearance, so it's going in to get punched out .020" over. I was beyond the service limit when I pulled it apart...
 

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If you are racing I would NOT go that tight with the next one, I would not go below .002". You loosen up a bit when you rev it all the time.
 

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Have you checked your piston to wall clearance to see what it is and how much you can hone it on a n.a basic rebuild nothing making more power I wouldn't add any more piston to wall check you piston to wall and i would give it a light hone and try not to take anymore metal out, basically just enough to brake the glaze and give the new rings a chance to seat
 

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I would read your piston package for clearances , they are all slightly different from one manufacturer to another and there different per application ie street , race , boost etc

Tom
 
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