I am posting for a fellow club memeber...
..would you re-ring the engine ? Leakdown test allow for a percentage of leakage for air that will get past the rings. Up to 15% was allowable on the chart we used. AS you can see his are worse. There was NO leakage past the valves or into the water jacket as the test showed. Rings are #1 suspect and cylinder wall
damage #2.
"Trent wrote"

Background-two+ years ago I did a full rebuild on my 77 2f
motor. Bored over .30 and milled the head to one hundred thousands. New everything. Since the rebuild I have never really had the power that I thought I should have. The first time I did a compression test( a week after the rebuild) each cylinder was around 120. I figured that the rings had not yet seated. Between then and now I got married and my wife had a
baby so the cruiser hasn't been driven more than 3-4 thousand miles. Recently I have had to drive it every day and it has run rough and has had no power. This morning I did a hot compression test and found 1,2, and 6 still were at 120psi and 3,4, and 5 were closer to 100psi. That led KenDahlberg and I to do a leak down test with a Yother tester. The test was
preformed at 65psi and the following were the results:

1-42=35.4% leak
2-54=16.9%
3-40=38.5%
4-59=9.2%
5-44=32.3%
6-60=8.3%

These numbers are a little disheartening. Every other cylinder is reallybad. We determined that the leak was in the rings not the head. I had the head of the motor a year after I built the motor, bad head gasket. The cylinders were clean and still had the machine shop cross markings in them. So what says the list? I know I should have been more attentive sooner after building the motor, but do you think the machine shop hosed me? I have
a hard time believing that there is that much wear in the motor. Any advice
would be apreciated. Thanks,

Did you send the pistons to the machine shop along with the block? I have heard that if you don't, there's a chance that there's enough variance in the pistons to do roughly this. So, I've heard it's a good idea to send the pistons along with the block, so the machinest can measure all of them, and if any are off, assign them to specific cylinders.

For those not familiar with a leakdown test..

For leak down test info check here... http://www.xs11.com/tips/misc/misc3.shtml

Yeah, the numbers aren't wonderful, but there isn't any point in fooling with it now unless the plugs keep fouling and it is blowing a blue smoke screen behind you. Tune it up and fuggedaboutit until you have a better reason to fool with it.

Is there any chance that some rings are on upside down?
Ring gaps pproperly staggered?
And that they just happen to be every other cyl.

Was the engine hot when the test was performed?
Sure you were at TDC for each?
Correct Valve lash?

Just thinking of some things that I have seen cause problems.

Cory

Originally posted by Lord Baskerville
Is there any chance that some rings are on upside down?
Ring gaps pproperly staggered?
And that they just happen to be every other cyl.

Was the engine hot when the test was performed?
Sure you were at TDC for each?
Correct Valve lash?

Just thinking of some things that I have seen cause problems.

Cory

Thanks for the input..

the ring thing could be a possibilty as the owner had the machine work done and he assembled but is knowledgeable of the process.
Valves were real close and we pulled the rocker cover and made sure we had TDC.
We are thinking that perhaps the rings to not match the overbore.

What make it so rings don't seat as we think has happened?

bennett

Ring end gap checked when assembled?
Clearance of rings in piston groove checked?
(too tight and rings may stick)

Once again... If the combustion ring (s) are upside down all sorts of wacky stuff may happen.

Cory

What type of rings were used?

One problem I have seen is folks use something like a good multigrade 20-50 from the start of a rebuild.... and the rings NEVER seated! :(

Always recommend using plain non-detergent 30W on a rebuild. Will run it the first 15 minutes (yes, minutes) drain and toss the filter. Refill with 30W... run about 500-1000 miles on it.... THEN go to a good multigrade of synthetic. :D

Tom

I'm the sap with the leak down problem. Thanks Ken for getting me on the list here.
The machine shop that did the work is very reputable. They ordered in the pistons as part of a full rebuild kit. I have been searching for the reciept but can't find it. Thats what happens when you get married, buy a house and have a baby. Not only did I lose my mind, but I lost all my records. This was the 4th motor I've built. 2nd cruiser motor. It has been too long for me to remember the particulars of the placement of each ring, but I know we double checked everything we did. That doesn't mean that I oculdn't have messed up somewhere.
For the engine breakin I have always run a 10-30 at idle 20 minutes and then changed the oil and filter. I then run the new oil of the same for a few hours at idle and change the oil and filter. I then drove the cruiser city driving for about 500 miles and changed everything agian. Then it's off to the races. Anyone that knows my driving style, I like the throttle when I am on road. This motor has not been babied, but has been well maintianed. My concern is that I am only getting maybe 8 mpg and call me crazy but i can feel the engine pulse. After the 2k+ to build that motor I'm left wanting and am willing to pull the thing down to get it right. I guess I should pull the head and take a look at the cylinders and rings.

[QUOTE]Originally posted by Trent Taylor
[B]I'm the sap with the leak down problem. Thanks Ken for getting me on the list here.

Welcome Newbie... :flipoff2:

I think you'll find great tech help here on PBB:bounce: :bounce2:

Trivia...... at 8MPG your paying .01 cent per 200' of distance traveled...sux man

could be worse... the USS John F Kennedy uses ten gallon of fuel per foot:eek: :eek:

Originally posted by bennett
...Welcome Newbie... :flipoff2: ...

Yeah, welcome dude! :flipoff2:

Too bad about your motor...:(

In my 68 (with a newer 2F)... I had a similar problem... When I first got the cruiser, the 2F ran great, but had all kinds of blow-by passed the rings.. enough that it would blow the oil filler cap off the engine... but crazy s it is, it ran fine... but thats not the goofy part...

We removed the engine and had it machined by a local machine shop, all went well and it seemed to breakin well, good power, etc. After a year, a routine compression test was done on the engine, sad looking results.. all were pushing 110-120 which seemed a little low for a 2-3,000 mile motor. We pulled the head for further inspection, all looked well. While the head was off, we wnet ahead and took it to the machine shop to have them double check it... All was in check..... put it back together and ran it... The cruiser is now owned by a kid in SLC but I estimate the engine has over 30k on it now and is still running strong...

Crazy...........:confused:

Trent,

Welcome aboard. :flipoff2: (friendly way of saying Hi to newbies here... ).

I've torn TWO engines that didn't seat the rings. Both rebuilt by good shops, but never built up full compression. Only thing in COMMON with them... good detergent oil when first fired up. One had chrome rings that never seated. Both of those engines were started with Castrol 20W50. Hmm..

In both cases, using the old ball hone to break off glazing and a new set of rings with the "non-detergent" break in oil... both were running fine. You really need to get the motor up to 2000-3000 rpm range, not sit at idle, to seat the rings.

I used to always think "low revs until everything is seated - best for camshafts, valves, bearings. high revs for rings"... Porsche does a full engine break in on every engine BEFORE it goes into the car. Complete dyno... fire up and RUN at 8,000 rpm for thirty minutes. :eek: Only thing that changed in recent years is to spin the engines without fuel nor coolant (big old motor revs them up... compression does the heating effect. I suspect it is easier on the bearings, but still does the trick. Environmental reasons being behind the change.

I realize some factory motors do NOT require a break in period, and start off the bat with a synthetic or good multi-grade... but they are also machined to precission processes or use a oil additive for that first oil fill. GM Engine Oil Supplement (part #1052368) is recommended with the rebuilt GM motor's. Personally haven't used it .

I've only built 30 motors... so limited experience. :) I'm way too slow to work in a commercial shop (25 hours labor of checking, and rechecking... vs. 6 for a commercial shop). :p

Tom :usa:

The break in could be it...

I allways run at 2K RPMs for 20 min then dump the oil and run normal.

Cory

Thanks for all the help guys. It looks like I will at least pull the head and take a peek. i talked to the machine shop today and they said to bring everything in to get measured. Chances are that everything is fine and the rings just didn't seat. We will see and then I'll pull the pan and replace them.

Trent Taylor

Originally posted by Trent Taylor
... We will see and then I'll pull the pan and replace them.

As bad as that sounds... it could be worse... a re-ring job can take an afternoon... not too bad considering the cost and time of pulling the motor... I'll keep my fingers crossed for you... hope for the best at the machine shop...
:D