Compression Test Results - Next Steps?

[Solace in Solitude]

At the bottom, you can see my compression test numbers...

For the past two days (its VERY hot in my garage), I have run a series of compression tests on my '78 40 (2F) - this is the first time I've compression tested it and, given how much power it has, I was surprised that the numbers were so low.

But, I was pretty sure the valves were not properly adjusted - this is the first chance I had to get to it. So, I adjusted the valves COLD and performed new 'cold' and 'hot' compression tests.

I then adjusted the valves HOT and performed the 'hot' tests again - this is where I am NOW.

With the valve cover off and the engine running, I see more blow-by around the number 3-intake valve than anywhere else - at least, that's where it appears to be coming from.

I will be removing my carb this week and sending it off to the FJJim-Spa, for a month or two and, while my carb is away, I have a 'virgin' intake manifold (from Georg) that I will be having milled.

Is there anything in the green results that indicates it would behoove me remove the head and have it milled and install a new head gasket, while my carb is away?

Is there anything that indicates a valve job would be a worthwhile endeavor during this period?

I'm looking for guidance/opinions - what should my next steps be?

Thanks!

Cylinder Cold Hot-Dry Hot-Wet Adjust Valves Cold Cold Hot Adjust Valves Hot Hot

1 115 110 123 115 110 110
2 111 105 100 121 110 111
3 104 100 100 100 95 101
4 105 101 115 110 101 110
5 111 108 109 111 101 109
6 105 111 118 121 115 115

 

[edwjmcgrath]

IF your compression test is done right, you're not seeing a big increase in compression with the wet test. That should say that the issue is more valve related than rings/cylinders. If you take the time to pull the head, I'd take it to a machine shop and have them do the valves/seals etc.

 

[want2wheel]

x2

 

[tls3601]

Agreed, if rings were shot some of your numbers would be lower. Mine was rebuilt approx 1000 miles ago. Reringed and complete valve job. Before the rebuild 2 of the cylinders on my 2F were reading 50

 

[vtgbeemer]

Interesting statement you made was that you were surprised given the power that the engine had that the numbers were so low. I assume your carb needed an overhaul but would imagine the engine ran smoothly . Just because your carb is going on vacation may not mean that now is the time to really spend that much time in a hot garage in Nevada. There are a lot of 40s running similar numbers and have been for years. Sometimes we force decisions where the gain doesn't justify the pain. Just an old guy's 2 cents.

 

[Solace in Solitude]

IF your compression test is done right, you're not seeing a big increase in compression with the wet test. That should say that the issue is more valve related than rings/cylinders. If you take the time to pull the head, I'd take it to a machine shop and have them do the valves/seals etc.

Since the wet test was done BEFORE I adjusted the valves, I'm gonna do another wet test in the morning, when it's possibly less than 100 degrees in my garage...

So, you said, "If you take the time to pull the head, I'd take it to a machine shop and have them do the valves/seals etc" .

May I expect to see an appreciable increase in compression, as a result of having the valves/seals, etc. done?

I don't have a problem pulling the head, I just don't have experience with this and don't want to set my expectations too high.

Thanks!

 

[Solace in Solitude]

Interesting statement you made was that you were surprised given the power that the engine had that the numbers were so low. I assume your carb needed an overhaul but would imagine the engine ran smoothly . Just because your carb is going on vacation may not mean that now is the time to really spend that much time in a hot garage in Nevada. There are a lot of 40s running similar numbers and have been for years. Sometimes we force decisions where the gain doesn't justify the pain. Just an old guy's 2 cents.

Thanks! That is kinda where I'm coming from in post# 5, above... I really don't mind pulling the head, if I can see an appreciable gain in compression, from a valve job. But, would rather do this when it's not so hot, as long as I'm not risking my 2F engine, by doing so.

Yes, it's running very well... and better now that I've adjusted the valves... but, 7mpg (before adjusting the valves) is much too low and who knows when the carb was last rebuilt. And the intake manifold has been welded and always has a bit of gas dripping from it - so, I'll replace the manifold when I put the rebuilt carb back on.

Now that I've straightened out a lot of the emissions and capped the EGR port under the carb, I'm going to do some additional vacuum tests - but, I haven't found any more leaks, since I capped the EGR port.

So, a Jim-rebuild/tuning is a good opportunity to get the carb back where it should be... and a good time for a valve job, if the rewards are worth it in this heat.

Thanks!

 

[edwjmcgrath]

What I was saying is that:
Low compression that doesn't improve with the wet compression test points to valves.
And if you've spent the time or money to pull the head off, it doesn't cost that much more to grind the valves and do the seals.

What I don't know is if you've done the compression testing correctly or adjusted the valves correctly.
If you have confidence in the testing and have confidence in the adjusting, you MAY see an increase in compression if you do the valves.

 

[Solace in Solitude]

What I was saying is that:
Low compression that doesn't improve with the wet compression test points to valves.
And if you've spent the time or money to pull the head off, it doesn't cost that much more to grind the valves and do the seals.

What I don't know is if you've done the compression testing correctly or adjusted the valves correctly.
If you have confidence in the testing and have confidence in the adjusting, you MAY see an increase in compression if you do the valves.

Thanks! I've never done any of this before, but, I followed the FSM and instructions found here on MUD. So, I'm as confident as I can be, at this point.

I'll do a post-valve adjustment wet test in the morning and, assuming the results are similar to what I saw with the pre-valve adjustment wet test, decide if I want to pull the head now or wait 'til it's cooler here.

Thanks!

 

[want2wheel]

If you are seeing blowby from the valves as the engine is running you have a valve that is not properly seated, and need a valve job to correct the issue.

 

[Solace in Solitude]

If you are seeing blowby from the valves as the engine is running you have a valve that is not properly seated, and need a valve job to correct the issue.

This is what I suspected - thanks for validating it!

 

[pb4ugo]

If you are seeing blowby from the valves as the engine is running you have a valve that is not properly seated, and need a valve job to correct the issue.

Huh? Blowby is the gases passing between the rings & cyldr wall. Usaully, smoke coming up thru the head would be coming from the crankcase, from blowby. Worn valves seats typically don't burn oil. Your numbers appear even, which is good, but they seem a little low. How many miles are on the engine? The way your numbers are posted is confusing to me. It's been a while since I had a f engine but I seem to recall the valves are to be adjusted when they are hot. Adjust the valves & do a compresssion test, dry & wet. I usually check compression when it's cold with all the plugs out & the throttle open. You just want the tests to be consistent.

 

[Cruiserdrew]

Do you know that your compression gauge is accurate? You numbers are pretty close together(That's a good thing), and if the engine runs well with decent power, I would be sorely tempted to just run it as is. Maybe get a second test gauge and test with that-make sure you trust the numbers. Does your truck burn a lot of oil or anything?

2Fs will seemingly run with almost no compression, though fuel mileage suffers as does power.

If you want to judge valves vs rings, you'll need a leak down test-that's better than a compression test and will give a much better idea about the overall condition of your motor.

 

[want2wheel]

The OP is the one that mentioned blowby seen from around the valves.
With the valve cover off and the engine running, I see more blow-by around the number 3-intake valve than anywhere else - at least, that's where it appears to be coming from.

 

[Solace in Solitude]

Huh? Blowby is the gases passing between the rings & cyldr wall. Usaully, smoke coming up thru the head would be coming from the crankcase, from blowby. Worn valves seats typically don't burn oil. Your numbers appear even, which is good, but they seem a little low. How many miles are on the engine? The way your numbers are posted is confusing to me. It's been a while since I had a f engine but I seem to recall the valves are to be adjusted when they are hot. Adjust the valves & do a compresssion test, dry & wet. I usually check compression when it's cold with all the plugs out & the throttle open. You just want the tests to be consistent.

I called it blowby... perhaps that's the wrong term? But, it seems to me that, in addition to "gases passing between the rings & cyldr wall", this same blowby could flow up past an incorrectly seated intake valve" - am I wrong? I'm seeing 'smoke' around the valve stems - it's VERY minor on all but the #3 intake an, even there, it's not a lot - just somewhat more appreciable than around the others.

I don't know how many miles are on my engine - the odometer has 93k, but I suspect that's not even the true mileage for my 40.

I've adjusted the valves, first cold, then hot and taken compression readings after each adjustment - I haven't yet done a wet test after adjusting the valves, but plan to do so this morning - it was simply TOO HOT in my garage to continue yesterday.

Do you know that your compression gauge is accurate? You numbers are pretty close together(That's a good thing), and if the engine runs well with decent power, I would be sorely tempted to just run it as is. Maybe get a second test gauge and test with that-make sure you trust the numbers. Does your truck burn a lot of oil or anything?

2Fs will seemingly run with almost no compression, though fuel mileage suffers as does power.

If you want to judge valves vs rings, you'll need a leak down test-that's better than a compression test and will give a much better idea about the overall condition of your motor.

My gauge is Harbor Freight - I also rented a gauge from O'rielly - the numbers were similar with both - my HF read a little higher, but both indicated the numbers were similar across the cylinders.

I haven't seen any indication of burning oil, but honestly haven't had a lot of opportunity to drive it yet - I got it in mid-March and spent the rest of our short spring fixing the steering and other things and getting it ready for solo trips to remote areas. Unfortunately the Nevada summer showed up early this year, so it's MUCH too hot to take it into the high desert - so, I'm trying to work around the heat and try to make sure it's solid for when the weather cools down this fall.

I'll post the wet test results later this morning. But, at this point, unless I see something different from the wet test, I plan on leaving it alone and driving it every chance I get - won't be much though until it cools down again.

Though, I may try to get a leak down test done on it in the meantime - I don't have the equipment, nor the experience to do it.

Thanks!

 

[Cruiserdrew]

I think that's a sound strategy. Maybe look for a low miles FJ60 motor to eventually swap in. Spend a year or two getting to know the truck, and then decide if you want to spend major $$ on it for engine work.

 

[Solace in Solitude]

I think that's a sound strategy. Maybe look for a low miles FJ60 motor to eventually swap in. Spend a year or two getting to know the truck, and then decide if you want to spend major $$ on it for engine work.

Thanks guy!

BTW it's 2400' here - I keep reading that elevation matters in compression testing, but nothing about 'how much it matters'...

So, here's where I stand, after adjusting valves hot, one more time - the dry tests are basically the same as my last dry readings yesterday.

The wet readings show an increase of 5.5%-13%, with an overall cylinder spread of 12%

Cyl. Dry. Wet. Incr%

1. 110. 119. 8.1%

2. 110. 121. 9.1%

3. 104. 116. 11.5%

4. 110. 120. 9%

5. 109. 115. 5.5%

6. 115. 130. 13%

Readings range, low to high (wet) = 14psifrom cylinder 3 (low) to cylinder 6 (high) = 12%

So, my wet readings are just above the 113.8psi threshold in the FSM and significantly below the 149.3psi optimum in the FSM.

Correct me, if you disagree...

1. There's nothing indicating a head gasket leak

2. All cylinders are consistently low and the 'spread' is not indicative of anything except a lot of wear

3. Odds are a valve job and/or new head gasket will not show an appreciable improvement

4. Best approach is to drive it and enjoy it, until I can find a low mileage FJ60 2F to swap in

An FJ60 2F is a direct swap

 

[JohnnyC]

I had scarry compression numbers in 2000 (115,98,35,32,89,119 dry) we had a good laugh and drove it waiting for it to die... it never died

put another 80K miles on it untill i couldnt take the leaks anymore (my wife more so than me in actuallity) instead of pulling it to replace all seals and gaskets... we put another low miles 1.5f back in it

drive it and enjoy it !

 

[Cruiserdrew]

T
Correct me, if you disagree...

1. There's nothing indicating a head gasket leak

2. All cylinders are consistently low and the 'spread' is not indicative of anything except a lot of wear

3. Odds are a valve job and/or new head gasket will not show an appreciable improvement

4. Best approach is to drive it and enjoy it, until I can find a low mileage FJ60 2F to swap in

An FJ60 2F is a direct swap

Elevation definitely makes a difference-I think about 3% per 1000 feet but don't quote me.

I agree with the above, except for #3. It is likely a valve job would result in better compression. But sometimes when you improve the top end of the motor, the bottom end can't take it, so it's a bit of a risk. If you do a valve job, you'll have no choice but to do a head gasket, but I agree, there is no indication your head gasket is a problem.

My 76 2F went for a decade with low compression, and when it failed, it was #5 rod bearing.

So drive and enjoy. If it uses some oil-that's ok, oil is cheap.

There are marginal advantages to an FJ60 motor and they run smoother too due to better balancing. It's basically a direct swap with minor differences in heater hose routing, fuel lines and carb linkage.

 

[Solace in Solitude]

I had scarry compression numbers in 2000 (115,98,35,32,89,119 dry) we had a good laugh and drove it waiting for it to die... it never died

put another 80K miles on it untill i couldnt take the leaks anymore (my wife more so than me in actuallity) instead of pulling it to replace all seals and gaskets... we put another low miles 1.5f back in it

drive it and enjoy it !

Wow! Your's were scarier than mine! I appreciate your insights!

Thanks!

Elevation definitely makes a difference-I think about 3% per 1000 feet but don't quote me.

I agree with the above, except for #3. It is likely a valve job would result in better compression. But sometimes when you improve the top end of the motor, the bottom end can't take it, so it's a bit of a risk. If you do a valve job, you'll have no choice but to do a head gasket, but I agree, there is no indication your head gasket is a problem.

My 76 2F went for a decade with low compression, and when it failed, it was #5 rod bearing.

So drive and enjoy. If it uses some oil-that's ok, oil is cheap.

There are marginal advantages to an FJ60 motor and they run smoother too due to better balancing. It's basically a direct swap with minor differences in heater hose routing, fuel lines and carb linkage.

Thanks Andrew! I appreciate your insights!

Since there's no indication that it needs a new head gasket, I'm not gonna pull the head and chance causing other problems right now.

It runs extremely well and will run even better after Jim rebuilds and tunes my carb. I am hoping to get the gas mileage up into the double digits with the carb rebuild - I don't really have time before I pull the carb to see how much improvement the valve adjustment may have made.

Thanks again everyone - I 'predicate it!

I'll drive the hell out if it after the weather cools down out here.

Thanks!