Need Opinions on What to Do with 3.0 Pistons and Cylinders??

lespaul · lespaul's Garage

I have a 1978 3.0 SC with Nikasil cylinders. Tearing down the top end for broken head stud replacement.

Assume 35K miles on the engine. No scuffing on pistons or cylinders. No marks or wear evident on them either. Cross hatching from original honing evident on walls of cylinders.

I have received two opinions on how to handle the pistons and cylinders.

Opinion 1 -- clean up with oven cleaner, replace rings and hone cylinders with grape hone on a drill (12 x passes).

Opinion 2 -- clean with ScotchBrite Red pad, I presume replace rings but do not hone cylinders.

I am not sure how to proceed. Would appreciate advice.

Thanks.

Eagledriver · 07-30-2014, 10:47 AM

If you measure the rings, you will find that they are better than any you can buy to replace them. Just clean with scotchbrite and re-use everything. At that milage they are virtually brand new.

-Andy

lespaul · lespaul's Garage

Thanks Andy. Wow -- is that the consensus?

tharbert · tharbert's Garage

Andy nailed it. If you measure it all and it's in spec, clean and reinstall.

lespaul · lespaul's Garage

I am convinced. However, I do not have the tools to do the measurements and have little confidence I would know what to do with them if I did. Where would one go to get the rings/piston's measured? Any good machine shop? If so, can anyone recommend a shop in the Southern Vermont, Western Mass, South Eastern NH region?

blpetry · blpetry's Garage

I had Tom Butler (tom1394racing) on here check my P&Cs and clean/recondition and/or replace anything that was out of spec. My parts came back looking like new. Super fast service and he sends you back a sheet showing all the measurements he took along with the factory recommended tolerances. Very satisfied customer, my engine is running great! Also he's (relatively close to you - CT I think).

Regards,
Brian Petry
Springboro, OH

Eagledriver · 08-01-2014, 06:24 AM

While taking them to a shop is always an option. You can do the critical measurements yourself with just a set of feeler blades. The hard part is taking the rings off the pistons and putting them back on without damaging anything. If you can do that, you can do the rest.

Measure the ring end gap by putting them one at a time into a cylinder. Make sure the ring is straight in the bore and then use the feeler blades to measure the end gap. You don't need to measure the oil rings. All the rings have a top and bottom so be sure to keep track or learn how to tell which way is up.

Measure the clearance between the ring and the groove in the piston with a feeler blade. The clearance should not exceed .004 inches. The clearance will be greatest at the top and bottom of the piston (6 and 12 oclock). If it's a little over .004 but you keep the old rings it will still work fine, you just won't get as long a life out of the engine (only 100k or so).

To measure the piston the cylinder clearance, you also can use the feeler blades. slide the piston into the cylinder (without the rings on). Measure the gap between the skirt of the piston and the cylinder wall. It should be less than .004 inches. The tops of the pistons (where the rings go) will have more clearance but that is by design. You can measure the ovalness of the cylinders by rotating the piston 90 degrees and measuring the clearance again. You can measure the taper by repeating these measurements at the top of the cylinder.

That's all you need to do. I don't have the ring end gap spec. handy but I think they are around .015 inches to .020 for a new spec and twice that for a wear limit. Like I said new rings are usually worse than your old rings.

-Andy

lespaul · lespaul's Garage

Thanks Andy. This is very helpful.

Walt Fricke · 08-01-2014, 09:26 PM

Brad - use the search function to look for terms like "hone cylinder" or "grape hone." You will find some skilled engine builders who will have nothing to do with any of this. Nikasil is tough stuff, and the most you can expect is to figure out how to remove any debris or varnish or whatnot which has nestled in between the Nikasil peaks.

Soapy water, or brake cleaner and a towel, or about anything you can spray in there and rub off, ought not to damage anything.

So do the research, and see what some of the professional engine builders have to say about this. Ignore where you see Alusil mentioned, as that is entirely different.

RedCoupe · 08-02-2014, 05:27 AM

I agree with everything said in this thread. Brad, if you reuse the original rings after determining they are in spec, just be sure to treat them like new rings for a few miles after you reassemble the engine. I wouldn't use a synthetic oil for a while, and I would use the load/unload technique to get the rings to reseat. One of the proprietary "break-in" oils isn't a bad idea for a couple of hundred miles. They typically have lots of ZDDP to protect the cams and rocker arms, but are purposefully less slippery than modern oils to help the rings seat. I didn't do this once with a low mileage engine that I reassembled, and I was never happy with the oil consumption after that.