Valve Job

[Greg Kingman]

I recently did a valve job (replacement) on my atomic-4. After putting it all back together, I am experiencing some popping back through the carbureator. The popping only happens when I increase the throttle. It idles smoothly. In examining the spark plugs there is a marked variance between all four. #1 is blackened and sooty, #2 is a bit lighter, #3 is absolutely whitewashed, & #4 looks tan colored and what I would consider to be normal.
Has any body else out there experienced these symptoms, and if so, where should I focus the attention of my troubleshoot?
Thanx for your input up front.
Greg

[67c&ccorv]

Did you put in new valve guides when you put new valves in the motor?

[Greg Kingman]

valve job

No I did not, however my machinist checked the clearances on them and gave them a thumbs up.

[adab1402]

Timing is everything

greetings ,the popping you hear ,comes from the intake valve being open on a compression stroke .assuming you did nothing to disturb the relationship between the cam and crank ,and your valves are adjusted correctly ,i would say you need to look at your dist timing ,a bit to advanced ,try retarding the spark ,by rotating thy dist counter clockwise ,say a smidge or two . best of luck . fair winds adab1402

[adab1402]

ps

i live in portland as well if you need advice or a hand 360-696-9710 m-f 10-2

[Greg Kingman]

valve job

Thanx so much for your input on my situation. I will pursue the possible issues you suggested and see if I can get some success. I will let you know what I found. Thanks again so much for your advice.
Greg

[67c&ccorv]

No I did not, however my machinist checked the clearances on them and gave them a thumbs up.

I am not a machinist or a mechanic - however, I am always leery about this kind of "thumbs up" check.

Were the valve seat surfaces refaced when you replaced the valves?

Measuring valve guide wear accurately requires the use of expensive bore gauges which are made in various stages of oversize and which you will seldom find in a mechanics tool chest - or for that matter in a machinists box.

If the valves were worn badly enough that you replaced them then I would argue the guides should be replaced also. I understand Don does not recommend replacing them unless the wear is greater than .004" but one man's guesstimate of .004" is another man's mile.

If it is not valve or ignition timing another possible cause of the popping noise is a leaning out of the mixture due to an air leak on either the intake or exhaust side of the motor...lets hope its not a pinhole leak in engine castings or cylinder linings! Check carefully intake and exhaust manifold mating surfaces and gaskets and carburator and exhaust pipe mounting flanges.

[Don Moyer]

Greg,

Another thing that you might recheck is the valve clearances. I hate to think how many times I got out of step in setting up each cylinder at TDC prior to setting the valve clearances in a particular cylinder. If you did somehow end up setting valves in a cylinder that was not at TDC, you could get symptoms similar to the ones you're describing.

Don

[lat 64]

My two cents

A compression test will tell you many things and eliminate some possibilities.

Popping back through the carb—I like adab1402's timing idea best.

But, if your compression and timing is good, then a poor distribution of fuel mixture is next.

A vacuum leak? Perhaps the manifold gasket got damaged or there is a little plug that you forgot to put in, or something that is leaning out one of the cylinders.

Too rich? Too much gas, like a stuck choke?

Say hi to those fine portland brew pubs for me

Russ

[Greg Kingman]

Valve job

Just to give a short update on my situation; I rechecked the valve clearances and found them to be a little off. #1 ex .012-int. .011. #2 ex. .012,Int..009 #3 Ex. .010, Int. .010 #4 Int. .090, Ex. .011. I will readjust these as necessary. In pondering the possible manifold leak, I remembered that I had replaced my old intake manifold which had some freeze damage with a used one that I found on Craigslist. I did not magnuflux it for cracks, so I have since sent it to the machine shop to perform that operation. As soon as I receive some new gaskets from Don I will be able to test my changes. Hopefully I will get to the bottom of it.
Again, thanks to all for the good input.
Greg

[Greg Kingman]

Valve Job

After magnufluxing my manifold, pressure testing it, and reinstalling it with new gasket, I think I have eliminated this piece as a possible source of air/water leakeage. The motor still coughs & spits back through the carb. when I increase throttle. Tweaking the timing by rotating the distributor helps minimize it but it is still a concern. Also the condition of spark plugs #2 & #3 being wet makes me wonder if maybe the head gasket did not seat properly between these cylinders. Is this unheard of? Please advise.
Thanx, Greg
PS
I took pics of the plugs but was unable to post them.

[Dromo]

wires crossed?

Check to see if you have the wires crossed on 3 & 4 spark- plugs
Rick

[adab1402]

just a thought

you may not be getting the advance you require on acceleration .take a peak at your advance and retard springs inside your distibutor . and if that looks good get a timing light at harbour freight and see what happens to your tdc mark on your flywheel when you give it the gun ,aka increase throttle,it should move to the right indicating an advance in timing .Im sure you checked your dwell as well ? fair winds adab1402

[Greg Kingman]

Valve Job

I can't find any mention in my manuals as to where timing marks on the flywheel might be accessed. Is there a simple way to expose that portion fo the flywheel? Also, does any one have a clue as to why two (2) thick head gaskets are standard fare on the Atomic-Four?
Thanx,
Greg

[67c&ccorv]

Greg, (from the manual)

"3) Plugs foul and engine misses (or misfires) on one or two cylinders, even though compression checks normal (85 - 125psi).

Likely cause factors:

a) Continuity in secondary cable has broken down to the failed cylinders - replace failed cables (plug leads).
b) Plugs faulty - probably from hair-line cracks in porcelain - replace plugs.
c) Distributor cap cracked - replace cap.

Note - It is very difficult to differentiate betweeen faulty plugs and faulty plug leads. Exhanging plugs between faulty and normal culilnders will usually determine whether the failure follows a particular plug."

MMI Universal Atomic 4 service and overhaul manual (1st ed., 1998)