What do you think of my compression

Over the weekend I did a compression check on my fhead and a manifold vacuum check and timed the motor for the first time. My compression readings where after being warmed up in the driveway for 2 mins only #1 110, #2 105, #3 102, #4 98. and after adding a small amount of engine oil to each cylinder I tried again and got #1 125, #2 110, #3 125, #4 110. and my spark plugs looked like this, cylinder number is in order with cylinder #1 on the right in the picture. Can anyone please explain to me what all this means as to the condition of the motor.

Pugs seem to all be light grey color except cylinder #4 which is brown.

 

The plugs look ok. maybe a little on the rich side, but that's how these older engiens run. I don't see any oil fouling - that would be what I'd expect if the your rings or valve guides were badly worn.

The compression numbers are ok. This engine has a low compression ratio, so the mean number around 104 is fine. Consistency is good, roughly +/- 5%. When you have trouble is when you have a lot more variability like 20% or 30%, or one low cylinder. You'd expect the compression to go up some when you add oil, and it does on all 4 cylinders - so not a lot to learn from that.

How old are the plugs? Deposits on #4 are interesting, but I'm not sure what to make of them.

Looks ok to me. I'd replace the plugs, write down the numbers in my notebook - and paste in some pictures? - and test it again in a couple of years.

 

plugs are about 1 year old, and I've already dated and recorded my numbers, The motor seems to run/ drive/ idle perfectly at about 615 RPM. But the engine does smoke some. It has the carter 1bbl yf 938sd recently rebuilt with a dual action AC 4693 nos fuel vacuum pump off ebay.

 

What color is the smoke? Is it present at all speeds?

The burnt-off deposits may be oil on #4, but I don't see it as a problem.

 

Overall the numbers look acceptable yet are certainly low compared to the ideal.
Ideal will be about 130 P.S.I. or higher across the board depending on engines exact CR.
Example: Mine is fairly recent rebuild with .030 O.S. pistons and the typical decked block and shaved head.
It reads higher than normal at 140 P.S.I. on all 4 cylinders.

The increase of your second reading basically indicates a relatively small amount of ring blow by.
But even on the second reading the numbers remain somewhat below ideal.
That then indicates valve wear or leakage.

Let's place the first set of numbers directly over the second set for a closer look.
110---105---102---98
125---110---125---110

#3 shows the greatest improvement which translates to increased blowby past the #3 rings
Low 2nd readings indicate #2 and #4 seem to have the worst valve seating.
I estimate this engine is perfectly servicable for a couple more years but it's service life is relatively short.
If the #2 and #3 exhaust valves are ignored for too long that can lead to block cracking between the exhaust seats.

 

Smoke is blue, large cloud after first start in cold weather. Then it dies down to where I can't see it from inside the jeep after driving 3 blocks. But it runs perfectly and idled awesome at 615 rpm idle.

 

I would also just be using it, at least until:
1) plugs start to oil foul, or
2) you get embarrassed when not actually performing neighborhood mosquito control

 

Im planning on a full rebuild within the next year, how much did yours cost? What brand of engine parts did you go with? Omix-Ada or USA made or? and do you have any tips for me? when you shaved your block, didn't you lose the engine serial number? or did you re-stamp it back in when done? There seems to be a place in Portland, OR that claims to specialize in older motors and says rebuild on that motor is about $1550 that I would probably take it to for the rebuild instead of a local shop that doesn't do anything but sbc 350's

 

This is the link to the place im considering having it rebuilt at even though it will take at least 2 round trips to get the motor to them and get it back at about $100 in gas per round trip plus food each time. http://www.portlandenginerebuilders.com/antique.html

 

Someone at my work recommended trying some Z-max. but I don't know if any of that stuff actually works or not. As far as I know my motor has never been rebuilt and being 54 years old, I see much more 15 year old Hondas and such smoking more than my motor. So id consider my motor pretty hard to kill. I also recently bought a 52 m38a1 with a seized motor, sitting uncovered for at least the last 3 years with the carb open as well as the radiator removed. After 2 days of soaking with PB blaster and tranny fluid, pryed on the ring gear and un stuck the motor and got it running with little effort. but It has ALOT of blow by

 

"It has ALOT of blow by"

Maybe the rings are still stuck.

 

That motor from the m38a1 is currently removed from the vehicle on an engine stand, and will have the pistons removed and probably just put new rings in it and new head gasket and used. At least that's the current plan. That motor also has a engine rebuild metal tag on the side of the block saying it was rebuilt at a Army base in japan in 1957 if I remember the date right. which is 2 years before my CJ5 was even manufactured, kinda weird that a military motor was rebuilt at 5 years old?

 

Military protocols called for their Jeeps to be sold off as surplus at less than 30,000 miles. No doubt they serviced them equally aggressively. Your tax dollars at work.

 

I agree. Sticky rings will act like that. Mine was so smoky I was embarrassed to drive it.
I picked up some stuff from the local boat shop called "power tune" from mercury marine.
Basically warm the engine, squirt this stuff down the running carb until it kills the motor. Let it soak for a couple hours, then restart the engine. I did this to mine several times and it runs soooooo much better, and I've been able to save many a mosquito because of it.
It absolutely will dissolve all of the carbon build up and will free up the rings. Change the plugs and oil when your done. No more smoke at all. Works like a charm!

 

Yeah, try freeing up the rings first- it may not be the problem, but you won't be out much either.

My 54 M38A1 has the F-head and it smoked badly before purchase. Got it home and tried tuning it but it always fouled the plugs before I could even get it warmed up. I researched my options and went with Kreen. Put an ounce or two in each cylinder and let it set. Did that 3 times over a span of 2 weeks. Then I put in some light engine oil, turned engine by hand a few times and fired it up. Smoked like crazy for several minutes, but ran long enough for me to set the dwell and timing.

Then I started driving it and the more I drove it the better it ran, until it began (within say 20 miles) to run great. The compression checks out to 135 across the board now and it has no blow by. I'm not sure what it means, but there are some numbers written on the inside fender indicating what I think are 4 compression readings and they all range in the 105 to 120 area. I'm not sure if that's what it is, but it seems likely and the readings I get now are much better.

So often, our jeeps are abused by POs: left to sit for years, poor maintenance, questionable fuel, etc. The carbs are old and not the most efficient, thermostats don't work or are missing, trips are short and the engine never really warms up, etc. The ring packs can get full of varnish and carbon from all that. Cleaning up an engine back 70 years ago was a fairly frequent occurence from what I gather (though partially that is from the lower quality fuel and oil of the day).

I don't mean for this to become a pros and cons of everbody's personal biases towards oil additives, but Kreen worked for me. Just my .02

 

Current rebuild on my daily driver only cost me $500.
Basically I bought an unused rebuilt Hurricane engine for $50.
I tore it apart without ever bothering to get it running.
I fully rebuilt this so called rebuilt engine.
Good thing I did because the bores were not consistant.

I have another Hurricane engine that's nearly complete.
This ones the final Hurricane engine for me.
Built from 100% genuine NOS Willys / Kaiser parts.
All it currently lacks 2 more NOS Kaiser (Eatonite) intake valves.
Total cost near $1500.

I have the original numbers wrote down somewhere but I don't bother to restamp the block.

I do everything else myself so that I can blame myself if anything goes wrong.
I install my own guides, gauge the bearings, retap all threads ... etc etc etc.
I do EVERYTHING that is Jeep related except only that I do not own any expensive milling or boring machines.
I take all my machining work to a 75 year old friend who runs his own machine shop by himself.
He has been rebuilding engines since the late 1950's.
When Dave quites machining engines, I'll likely quit building engines.
Next up D-225. Here again I use 100% NOS GM or Jeep parts.

 

since im not at all confident in my engine rebuilding prowess. and I don't want to ask a buddy or brother to do it and risk them feeling bad/ responsible if something happens I would be paying some shop to do it. I would install and remove the motor myself but that's about it. In an attempt to increase compression and possible free stuck anythings in my motor (and im talking about doing this to my currently running well, idling perfect just smoking some 59 CJ5 Fhead with lower compression readings) I think I would like to try some of that Marvel Mystery Oil that you guys are talking about. My motor is just about time for another oil change, so how would you guys recommend running this stuff through? After the oil change I assume? What if I tried something like that Mercury Power Tune that rkarr recommended, and do it like he said 3 or so attempts. Then change the plugs and oil and add Marvel Mystery Oil to it at that time? or should I try something like pour some Sea Foam into the spark plug holes and let it sit overnight then pump it out and run the motor and then change the oil and add MMO to it?

 

Well you can always buy a bottle of "total engine rebuild" in the 16 oz.spray can.
I hear that Walmart has the best prices on it.
Sorry to be blunt but....you get my meaning.

 

If you take your time get yourself a manual you could do it, F heads are fairly simple engines. And you can learn allot by doing it and save yourself allot of money. And these guys here are always ready and willing to answer questions if you get stuck. there is even good pic's and directions on the cj3b page.

http://www.film.queensu.ca/cj3b/Engine/Rebuild.html
http://www.film.queensu.ca/cj3b/Tech/EngineRebuilding.html