Scratched cylinder bore

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68gtxman

68gtxman

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Well, other than that Mrs. Lincoln, how was,the play?

Just took off the heads on my recently purchased 340 engine and found one cylinder bore scratch by the wrist pin! Looks like the scratch is about .012" deep by about 3" long. Otherwise, the bores all look great - they don't even have a ridge at the top.

I first thought i'd be ale to reuse all the pistons, though I haven't miked the bores to see how they are. Would it be wise to sleeve the one bad bore if all the others are close to original specs?

Anyone got some upbeat words for a bummed out Mopar man?
 
I had to sleeve mine a coupla times over the years, they have held up well,, and is still a #'s matching, car,, and it wouldn't have been without sleeves..

Running 12:1 pistons since sleeves,, no worries..
 
Pics?
Need to see how bad it is, maybe limp it till u can rebuild it, as of now that's my opinion.
How did u know to go through and look, was it burning oil?
Pics, how wide a scratch?

If its bad enough that u can't go .020 over on that one hole while u can with the rest...just sleave it.
 
View attachment Scratched Piston.jpg

The scratch is the brown stain looking thing, about 3/16ths wide at the widest part.:violent1:

The engine is not in the car. I bought it from a FABO member earlier this year (he got it from a friend who never used it, who also got it from another guy but didn't know the history). I just got around to pulling it apart on the engine stand, so I could start the rebuild. I see that the head on this side had been previously removed (loose head bolts), so I guess that a previous owner pulled it to see why the compression was low on this side. The oil pan was filled with gunk (no metal pieces though) and the timing chain was as loose as a jump rope. This engine was put through its paces, but amazingly it had no ridges at the tops of the bores.
 
Or it was ridge reamed and dingle balled like a member on here's 340 was when I pulled it apart to see why it had 60% leakdown.
Cool part is it'll go.020 over, hope urs does too. Good luck
 
No, there are no signs that anyone cut down the ridges. None of the cylinders have any signs of cross hatching - even on the portion that the rings never touch. Did the factory ever leave off the cross hatching?
 
Yep! If you got a real good Machine shop that you trust this is No Big Deal. It's gotta be cleaned up and then measured. Right??
 
sleeve it. No problems and you can reuse the pistons...I think a sleeve is about 40-100 depending on who you go with. PAW used to sell "restored" 340's sleeved back to std. bore.
 
What size is it now?
Sounds like you are up for a total rebuild.
.012 gouge X 2 is a .030 over bore, when you add up taper on the cylinders.
It may clean at .040 but I doubt it.
 
hatching could be just worn away. In all honesty it is out of the car I would mic the bores first. The issue might be more obvious than what you think at that point.
 
I've had a couple of these over the years. It's common for the plain lock rings to wrok out or break under hard abuse, then the pin moves around and gets the bore. That one piston will bneed replacement - I wouldn't trust just sticking a new lock ring in that groove. So you're looking at a sleeve and pro honing plus one piston of the same type as you have. That's not considering taper in the bores. With signs of abuse as you note - the ring lands are probably worn too. So if it were me, I'd just expect to rebuild the lower end properly, stick in some oversize pistons (or a performance improvement set of hypers) and go that route. For the long run, you know it's hurt - it needs work to last.
 
You may want to have it sleeved.


Did you hear about the "sleeve" theory for loose women? If you have a woman who is a little "loose" down there, you need to sleeve it. Stick a 10 lb ham up there and pull out the bone. Now it is sleeved and will be nice and tight, just like new....
 
Moper's right, and that gouge will your rings up fast, no way around it.

Sleeve it. Think: EVERY aluminum block is sleeved, even top fuel. (Excepting GM's little disaster from the late '70's.)
 
Thanks for all the thoughts and great advice! You are the reason that FABO is the best!
 
I finished the total tear down and found some amazing things:

- 7 out of 8 pistons had the top ring broken
- 1 piston also had the 2nd ring broken as well as the top one
- the piston in the scratched bore had two different type of clips on the wrist pin - the side at the scratch had a wire type clip while the other side had the normal stamped steel ring clip.

The last point tells me that someone tore down the engine before me to replace the loose wrist pin clip, totally ignoring the scratch while putting it back together. This piston had no marks on it whatsoever from the original clip, so that probably means that it was replaced. That same guy probably pulled all the pistons for an inspection, and when he reinstalled them using the original rings, he forced 7 of the top rings to the point of breakage. When he was done "rebuilding" the engine, it probably had a terrible miss in the cylinder with the two broken rings. I'd like to know who this guy was so I could stay away from his shop!

Well now I'm all ready for the machine shop. I will probably need to buy at least one piston as I dropped one on removal and snapped off about 1/4" off the skirt on one side. Oh well. It also looks like the bores are 4.04" per my calipers. This doesn't mean they aren't barreled. I'll let the machine shop check this out as I don't have the gauges.

Do I need to have the crank balanced for street use? What do you suggest?
 
Assume it needs to be bored, the shop can tell you what oversize to buy the pistons. If you buy non-factory pistons then you don;t have to balance. Personally, I don;t use factory balance jobs, nor do I like external balancing. So I'd use KB hypers to get some compression, have it internally balanced, and know it's done right.
 
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