Compression test results

[Patrick L.]

'A fluttery vacuum reading'. How does the engine run ? If it runs good, why not just check/adjust the valve lash and run it ?

[christian]

Took a closer look at the pistons and cylinders, turns out what I thought was a ridge turned out to be nothing but carbon build up, wiping the cylinders down with a paper towel removed pretty much all of it. Also, cylinders had a .060 stamped on the tops, this sounds dumb, but since I'm new to all this, that means I should purchase the 60 oversize rings right ?

[christian]

Originally Posted by Patrick L.

'A fluttery vacuum reading'. How does the engine run ? If it runs good, why not just check/adjust the valve lash and run it ?

It runs great except for the annoying off idle stumble and blow by. Before I threw a draft tube on the filler tube I'd always have oil all over the hood louvers and drivers side fender.

I understand the slight fluttering, but swingin wildly from 16 to 23 seems to be indicating something wrong.

[Tom Wesenberg]

If you have blowby, then I'm sure you'll benefit from a set of .060" oversized rings. If I had a vacuum port I could connect a vacuum gauge to my 28 for a comparison of readings, but as others have said, you might just drive it since you have pretty good compression readings. Have you looked at the top ring gap yet?

A 4 cylinder won't give a real smooth vacuum reading. I would look more for a sudden drop which could indicate a slow to close valve.

[christian]

Well I just had to know the condition of the pistons and rings, I jacked up the car and dropped the pan, then unbolted the rod big ends and brought out the pistons. Attached are some photos of them. In short, I think they look pretty bad, but what I dont get is why they look so bad, as the bore is extremely clean, there are no cuts or scratched in the cylinder bores what so ever, its almost as if the pistons came out of another engine.

Next as Tom suggested, im going to remove the rings, and check the gaps inside of the cylinders.

AS far as the pistons go, what do you guys think? junk them or throw them back in with new rings after I hone the bores nice nice.

Also connecting rods had some pretty beat up steel shim packs, should I reuse them, or throw in a new pack? if so keep the steel or go brass ?

[Tom Wesenberg]

Sponsored Links (Register now to hide all advertisements)

I wonder if someone ran the engine for only a few minutes, then let the car set for a long time. It kind of looks like corrosion has made the marks on the pistons. Check the rings fro side clearance in the piston ring lands. If they are nice and snug, and the skirt side clearance in the cylinders is OK, then replacing them is a toss up. Also the wrist pins need to be snug, like .0003 to .0005" inch clearance. A set of pistons is about $80 to $100, so it's not a big deal to buy a new set.

[Mitch//pa]

Christian you don't mess around i like that...

[Tom Wesenberg]

Originally Posted by Mitch//pa

Christian you don't mess around i like that...

Yes, I was thinking the same thing. You'd think he was on the clock and trying to beat flat rate.

[christian]

Originally Posted by Tom Wesenberg

Yes, I was thinking the same thing. You'd think he was on the clock and trying to beat flat rate.

Well I have to admit, my mother in law was watching our kids for the night...carpe diem i suppose.

The piston pins fit very very snug. the piston and the rod both easily rotate about the piston pin, but cant rock off axis at all so I would say they are perfect. Which is why I am hessitant to swap pistons unless I have to. Unfortunatly I have to work a double today, wont be able to check ring gaps today, hopefully tomorrow.

thanks or all the insight.

[christian]

Once I get the chance I'm going to remove the rings and insert the bare pistons into the cylinders to check wear , what kind of clearance is acceptable between piston and cylinder ?

[Patrick L.]

Generic clearances, ring end gap- .003" per inch of bore. Piston to cylinder wall- .001" per inch of bore.
Manufacturers will have their own specs.
Ford wants .002" piston to wall.

[christian]

Originally Posted by Patrick L.

Generic clearances, ring end gap- .003" per inch of bore. Piston to cylinder wall- .001" per inch of bore.
Manufacturers will have their own specs.
Ford wants .002" piston to wall.

That piston to wall number, is that with rings installed or bare piston pushed to one side ?

[Purdy Swoft]

Ford used split skirt pistons. I would think that the pistons pictured would need .004 .The gap could be more but not much less. I use a long blade feeler gauge to measure the gap. I measure the ring end gap and if the gap is way too big, I go toThe next larger size ring and file the end gap until I get the correct gap. This gives more ring spring pressure against the cylinder wall to help compensate for wear. I would pay close attention to ring gap in the cylinder with lowest compression.

[Patrick L.]

yep, what Purdy said.
I like the .001" per inch of bore for most pistons, even at that, I tend to run them a bit looser. They usually won't 'rattle' until they are quite a bit looser than that. To check piston to wall clearance when the engine is apart I use a micrometer/snap gauge. If the pistons are still installed then I'll use a feeler strip to get a good idea of what the clearance is especially when looking for a 'rattler'.
Ring end gap is something that a lot of folks don't bother with, its pretty important though. I think its better to run the end gap a bit looser than too tight, but, best to run them 'just right'.

[christian]

I callerd my wife, she was nice enough to check the end gap, i had the rings off already so fugured it was easy enough for her to do. I walked her though it, placed the #3 compression ring in evenly in the bore, she stated that while in she was able to slide a .034 feeler gauge in the gap and that it was still wiggling a bit, she couldn't find my other larger feeler gauges. Guess I picked a good wife .....

[Purdy Swoft]

Sounds like you've got a real good one. Most couldn't or wouldn't even try!! The ring gap need s to be measured evenly in the bore, just above where the rings stop at the bottom ov the stroke. The upper cylinder will be larger and have more gap caused from expansion from all of the explosions when the engine fired on compression. Upper ring gap should be .012 to .015 . Over size rings will help and probably last a good while. It still won't be a new engine.

[christian]

Can the oversize rings be filed without special tools or is it necessary to use a ring grinder ?

[Patrick L.]

.034" ? Geesh. Thats a few 'tads' too wide. Use a grinder ? Hmm, nope, not me. A file works for me. The ring does need to be 'square' in the bore, I use the piston to set them. I know you knew that though, the .034" kinda gets me. Maybe the builder got the spark plug gap and ring gap mixed up[smiley face].

[Purdy Swoft]

I place a file in the vise with the blade sticking straight up. I stand in front of the vise with ring in hands and work the ring up and down with the end gap against the sides of the file. It can take a while, but I check often to make sure that I don't remove too much material. A ring grinder would be nice but I'm a po country boy.

[christian]

Originally Posted by Patrick L.

.034" ? Geesh. Thats a few 'tads' too wide. Use a grinder ? Hmm, nope, not me. A file works for me. The ring does need to be 'square' in the bore, I use the piston to set them. I know you knew that though, the .034" kinda gets me. Maybe the builder got the spark plug gap and ring gap mixed up[smiley face].

Or maybe snapped a new oversize ring (engine is 60 over ). And just slapped an old one in