cross hatching flexhone or stones

[70spider]

Well I have been putting it off for some time now and finally did a compression test on the "recently" rebuilt engine. It was bad, 90psi then added a bit of fresh oil and it it went to 130psi. So the conclusion is the rings didn't seal. I did a bit of learning and found out that the the cross hatch the shop put on the walls was very fine and apparently you want a course hatch for iron rings. So now my only option is to pull the engine and do it my self.
My question is there is a bunch of conflicting preferences on which tool is best. Note the engine has less than 700 miles on the rebuild so which would best? stones or a flexhone ("berry-ball") ? I know I will need 220-240 grit.
I anticipate the bearings being washed so I'll replace those while I am in it.

[18Fiatsandcounting]

Could your low compression be due to valves not sealing? Are your tappet clearances OK? Is the 90 psi on all cylinders or just one of them?

Another possibility is that your cam timing is off. Being off by a tooth on the intake cam pulley in the wrong direction can dramatically lower your cranking compression.

-Bryan
PS: If you need to do a new crosshatch on your cylinder walls, I use a "dingleberry hone" and a hand drill. Look up Brush Research Flex Hones, for an 80mm bore.

[70spider]

It was 90psi on all four, and jumped up to 130 psi when oil was added to the cylinder. I did some more research and since it was bored most think the dingleberry is ok.
I went to the website and found a 3.00" to 3.25". My bore is 80.4mm or 3.17". I read their sizing suggestions and they suggest the hone should be slightly larger than the bore, so I think it should work.

[18Fiatsandcounting]

That hone sounds like the right size. But are you going to remove the engine and tear it back down to do the honing?

I'm still thinking you might have some valve problems. I would make absolutely sure that your valve timing is right, before tearing down the engine. Incorrect valve timing can give very low compression readings.

-Bryan

[70spider]

Well the reason that prompted me to test compression was the engine was getting fuel into the crankcase and oil pressure would fall off after the engine would get hot (probably due to the fuel thinning the oil). So I removed the mechanical fuel pump and tried an electric pump with a fresh oil change. I drove it for about 50 miles and checked the oil and still was getting fuel in it. So next step was to check the rings.

The compression went up when I added a couple of tablespoons of fresh oil to the combustion chamber, to 130psi. From my understanding the "add oil test" is suppose to eliminate the valves as an issue if the psi increases significantly. As it was explained to me; if the valve is stuck open then the psi would not go up. I checked the valve lash gaps and they were spot on, 0.018" on the intake and 0.020" on the exhaust.

This was my first attempt at rebuilding an engine and did not know enough about cross hatching. When I did some research and discovered that a very fine cross hatch is more for modern engines or moly rings I went back and looked at the photos I had of the block after the machine shop. The cross hatching was very faint, it felt smooth to the touch as I remember. So this is why I suspect the rings didn't seal.
I plan on pulling the engine when I can, probably in the spring.
Thanks for the help Bryan

[18Fiatsandcounting]

A few thoughts:

1. You are right about the oil test, but if you add too much oil, it will "take up space" in the combustion chamber and artificially raise the cranking compression. At least until the oil is pumped out of the engine. I'm thinking a teaspoon of oil, so 2 tablespoons might be too much.

2. It sounds like your engine is running rich if you still get gas in the oil after you changed to an electric fuel pump. This rich condition would wash down the oil on the cylinder walls and could have been part of the reason your rings didn't seat.

3. Oil pressure will fall as the engine heats up, that's normal. I've had many Fiat engines that started out at 55 psi when cold but then dropped to 20 or 30 psi when hot. These engines were fine.

-Bryan

[70spider]

"2. It sounds like your engine is running rich if you still get gas in the oil after you changed to an electric fuel pump. This rich condition would wash down the oil on the cylinder walls and could have been part of the reason your rings didn't seat."
Maybe, it always ran rich even in Kansas with the stock Weber 32/36 jetting leaned out 1 size.
"3. Oil pressure will fall as the engine heats up, that's normal. I've had many Fiat engines that started out at 55 psi when cold but then dropped to 20 or 30 psi when hot. These engines were fine."
Mine starts out at 45 and drops to 5 with 20w50 oil in about 15 minutes, what i think is due to the fuel in the oil.

This is what my cylinder walls looked like after the machine shop:

I know the image isn't the greatest but as you can see there was almost no crosshatching. At the time I had no clue about crosshatching and its importance. I just assumed once I got it back from the machine shop I just had to clean it and reassemble.

At this point I can't sell the car 'cuz it's crap so might as well give it another shot.

Thanks again Bryan, Have a good Christmas.

[18Fiatsandcounting]

It's hard for me to tell from the picture, but yeah, I see what you mean. It doesn't look like the cylinder walls were prepped very well. Also, if your oil pressure is dropping that low even with 20W-50, then it sounds like your bearing clearances are too large as well.

I hate to ask, but do you trust your machine shop? Is there another (knowledgeable) person that you could ask for a 2nd opinion?

-Bryan

[70spider]

"I hate to ask, but do you trust your machine shop?"
I am currently in NM and the only shop is a 150 miles away. I haven't used a shop here so no.

"sounds like your bearing clearances are too large as well"
I had the machine shop that I used in Tulsa check the crankshaft and he said it was ok. The engine never dropped more than 5 psi before the rebuild.
During the rebuild I plastigauged it and it was good. I plastigauged it a second time after rotating the crank a 180 degrees and all was good.
The oil pressure didn't drop when I was running the car at first but after about 300 miles it started dropping and getting worse.

So my plans at this point is to tear it down, check the cylinder bores and crank, then crosshatch the cylinders, replace the con rod and main bearings, and pray it all works out.

[18Fiatsandcounting]

So my plans at this point is to tear it down, check the cylinder bores and crank, then crosshatch the cylinders, replace the con rod and main bearings, and pray it all works out.

I hope it works out. I think it depends on what you intend to do with this engine. If you want to race it and spend most of your time at 8000 rpm, then no, this isn't the engine for you. If you want to just have fun and enjoy a 50+ year old car, this engine might be perfectly fine.

You're at a pretty high altitude, and carbureted cars can struggle with that. Less air, so they tend to run rich unless corrected.

-Bryan