Rebuilt Motor

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VinceBlack

Member
After running rebuild engine over 900 miles I am having carbon buildup on no. 1 cylinder, the other 3 look normal. A compression check showed cylinder 1 was at 60, 2 at 70, 3 at 85 and 4 at 90. What would be normal reading, engine has a vibration and I'm wondering if the difference in compression could be the problem. Ideas?
 
VinceBlack said:
After running rebuild engine over 900 miles I am having carbon buildup on no. 1 cylinder, the other 3 look normal. A compression check showed cylinder 1 was at 60, 2 at 70, 3 at 85 and 4 at 90. What would be normal reading, engine has a vibration and I'm wondering if the difference in compression could be the problem. Ideas?
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Did you Align your rods before you put them in, as it sounds like you have oil going past your rings.

That will never fix its self.

Herm.
 

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Carbon build-up from burning oil due to oil control ring not seating for the full stroke?

And alignment as in co-linear (parallel) between crank pin and piston pin?

Victor Page works with this.
521179.jpg

With the head removed you may be able to see the "squirm" as the piston rotates back and forth through a small arc.

Joe K
 
Do you have a high compression head? Compression pressure should (roughly) be the compression ratio x atmospheric pressure (14.7 psi at sea level and 68* F). A 6:1 CR would relate to the #3 and #4 readings. A stock 4.2:1 CR would relate to the #1 reading.
 
gee,could be anything..ring gaps in line,bent rod,leaking valves you name it...was the engine cold when tested ? hot? did you do a wet/dry test?or a leak down?are you using engine oil? is your flywheel and clutch balanced? did you align the flywheel housing to the crankshaft?..
 
"Take it back to the rebuilder." Or, at the very least give him a call with your concerns. If you start pulling heads and stuff the rebuilder may tell you that it was fine when it left his shop.....
Most of these folks want to know when something goes wrong and find out why so it doesn't happen again.
Keep us posted, Chap
 
I had motor built by shop that I trust and am talking with him. I guess my main concern is the uneven compression. What is causing plug to build carbon. Could be weak or late spark to #1? This is my first A engine so have nothing to compare it to. As far as the way it performs, runs strong, nice even idle. I guess I'm comparing it to a modern 4 cylinder on their smoothness. I am building a adapter for a leak down test. No smoke, no oil consumption.
 
How are you confirming you have carbon build up?


My motor which was rebuilt last winter did not give me reasonable compression readings until it had about 1200 miles on it, when the rings seated properly and the valves seated properly. I was getting readings all over the place from 50 - 78 lbs. Now they are all 75-78 lbs. Gas mileage was only about 8 MPG, now is 16 mpg.


If not familiar with the A, spark plug reads are different than more modern cars. Everything on the end in the combustion chamber is black (but not sooty/powdery), except the center electrode. It should be a light to dark tan. If black the motor/carb is running rich, if white the motor/carb is running too lean. If oily then ring issue - but you would probably be seeing blue smoke out the exhaust, especially at start up. Best way to check is to put in a new set of plugs. Go out and run it for a couple of hours at varying speeds 25-45 mph. Let off the gas and push in the clutch, turn the ignition off and coast to a stop somewhere, and pull the plugs to read them.


When Slowing down, or shifting, do you hear a slight popping sound from the carb - usually means you are running too lean - the sound is a slight carb backfire.


My motor was pretty bad, blown head gasket, cracked rod cap, lots of other issue the motor builder found. lots of vibration above 30 mph. Was a lot better when rebuilt, but has smoothed out a lot more over time and 1400 miles. I know of another person had their motor rebuilt last winter, we are experiencing the same things. Takes a while for the motor to break in and smooth out - especially if you are following good break in practices and very frequent oil changes.


Let us know what you find out, it is good you are going back to the motor builder to express your concerns. They are used to answering these types of questions, and if something is abnormal it lets them be aware of it and do not get blindsided.
 
Last two posts make sense, I drive car most every day, normal drive is around 40 to 60 miles, the sweet spot is about 38 to 43 mph, all the vital signs run normal so could be I'm over concerned. Thanks for help, planning a long trip want it to be reliable
 
My truck had a 4.11 rear end, and I had a 3.54 put in . Now is very smooth up to 35, 35 -50 is happy but a little busier, but not really what I would call vibration. Above 50, yes it has some vibration, at 55 it is turning 2300 RPM, more than that is not really great for the motor or my nerves.


During the build of a motor there extras you can pay for to smooth things out for a touring motor. Balancing , counterweight, making sure all the rods/pistons/valves are the same weight.


Personally I am happy with what I have, I like a slower pace with no worries of overdriving the brakes, not having to spend tons more money to make the steering and brakes perfect. Am very happy only driving 30 -35 normally enjoying the slower pace, and 45-50 when I have traffic behind me.


Some/most who do a lot of touring have some or all of teh following - high compression heads, different cam, non-stock carb, performance exhaust and or intake manifolds, Mitchell overdrive, etc., etc., and their cars are extremely nice, almost as good as a modern car.


So what did your motor guy have to say?
 
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