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Old 01-15-2008, 08:00 AM
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Default Let's Talk Compression and Cam Timing

Doing some tweaking on the engine and trying to determine if I should press Toyota for a new short block or not. Did a compression test exactly like the FSM says. Let's call them dry numbers (also I need to adjust the valves).

#1 - 135
#2 - 130
#3 - 125
#4 - 135

Well those are crap. And I mean utter, complete crap and actually 5 to 10 psi lower than anything I've seen before (some of which is probably the valves needing adjustment).

So I do the next step, which is a wet compression test with a spray of oil. Keeping in mind that this is 8PM at night, it's dark in my garage and I'm trying to use a turkey baster to spritz a small amount of oil into the plug hole without coating everything else. It's like painting a 1/16th scale model with a 4" brush.

#1 - 140
#2 - 145
#3 - 150
#4 - 160

OK, now I'm scratching my head. When it occurs to me that how much oil I spray into the combustion chamber probably has an effect. So I try #2 again, spraying just a little more oil in and sure enough.

#2 - 160

So like a V8 commercial, I slap my forehead with my hand and say to myself "Duh, you are spraying an incompressible fluid into the chamber." So I'm starting to think that my previous dry/wet tests that show a 10, 15, 20 or 30 psi jumps in compression might be partially or maybe pretty much completely bogus.

Based primarily on the #1 dry/wet jump of 5 psi I'm less convinced I need to beat up Toyota at this point. Two things jump to mind, that my $20 compression tester is a pile of junk or that my cam timing is really the issue here. The engine does not run like it's only got 125 psi of compression, it runs pretty decent. Not losing oil, oil is not getting dirty, no smoke, no mixing of any fluids, no oil blowing out of the dipstick. The problems are settling the idle down, it's pretty lumpy, and I get this weird stumble in one cylinder every couple of cycles (say a little pop once every 2 seconds at 2500 RPM) if I hold the throttle steady. So I'm starting to think maybe my chain is off a tooth or the cam lobe profile is not quite centered. In any case I bought an adjustable cam gear a while ago and never used it (I was thinking I would deck the block when I built an engine, which definitely throws the cam timing off).

So who's degreed a cam? I don't have the stuff to do that, so driving in this morning (remembering that I was at the time still not properly caffeinated) that I could put the cam gear on and bump it a little advanced and a little retarded and watch the cranking compression go up or down. That seems pretty ghetto, but really the danger would be if I'm already a tooth off adding more advance or retard might crunch a valve. Does seem safer than trying to guess which way I might be off a tooth and moving everything a whole tooth (which is about 2 degrees I think).

So any thoughts?
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Old 01-15-2008, 08:11 AM
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Originally Posted by DaveInDenver View Post
Doing some tweaking on the engine and trying to determine if I should press Toyota for a new short block or not. Did a compression test exactly like the FSM says. Let's call them dry numbers (also I need to adjust the valves).

#1 - 135
#2 - 130
#3 - 125
#4 - 135

Well those are crap. And I mean utter, complete crap and actually 5 to 10 psi lower than anything I've seen before (some of which is probably the valves needing adjustment).

So I do the next step, which is a wet compression test with a spray of oil. Keeping in mind that this is 8PM at night, it's dark in my garage and I'm trying to use a turkey baster to spritz a small amount of oil into the plug hole without coating everything else. It's like painting a 1/16th scale model with a 4" brush.

#1 - 140
#2 - 145
#3 - 150
#4 - 160

OK, now I'm scratching my head. When it occurs to me that how much oil I spray into the combustion chamber probably has an effect. So I try #2 again, spraying just a little more oil in and sure enough.

#2 - 160

So like a V8 commercial, I slap my forehead with my hand and say to myself "Duh, you are spraying an incompressible fluid into the chamber." So I'm starting to think that my previous dry/wet tests that show a 10, 15, 20 or 30 psi jumps in compression might be partially or maybe pretty much completely bogus.

Based primarily on the #1 dry/wet jump of 5 psi I'm less convinced I need to beat up Toyota at this point. Two things jump to mind, that my $20 compression tester is a pile of junk or that my cam timing is really the issue here. The engine does not run like it's only got 125 psi of compression, it runs pretty decent. Not losing oil, oil is not getting dirty, no smoke. The problems are settling the idle down, it's pretty lumpy, and I get this weird stumble in one cylinder every couple of cycles (say a little pop once every 2 seconds at 2500 RPM) if I hold the throttle steady. So I'm starting to think maybe my chain is off a tooth or the cam lobe profile is not quite centered. In any case I bought an adjustable cam gear a while ago and never used it (I was thinking I would deck the block when I built an engine, which definitely throws the cam timing off).

So who's degreed a cam? I don't have the stuff to do that, so driving in this morning (remembering that I was at the time still not properly caffeinated) that I could put the cam gear on and bump it a little advanced and a little retarded and watch the cranking compression go up or down. That seems pretty ghetto, but really the danger would be if I'm already a tooth off adding more advance or retard might crunch a valve. Does seem safer than trying to guess which way I might be off a tooth and moving everything a whole tooth (which is about 2 degrees I think).

So any thoughts?

Twin overhead isn't it? Two cams to degree! For our high altitude and normally aspirated 2-3* advance on the intake and 2* retard on the exhaust cam will make a huge difference! If it was charged then lest intake advancing and more exhaust timing will add several ponies! You want to keep your overall advancing to around 4* and not over 6* or you start stressing the rods.
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  #3  
Old 01-15-2008, 08:15 AM
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Twin overhead isn't it? Two cams to degree! For our high altitude and normally aspirated 2-3* advance on the intake and 2* retard on the exhaust cam will make a huge difference! If it was charged then lest intake advancing and more exhaust timing will add several ponies! You want to keep your overall advancing to around 4* and not over 6* or you start stressing the rods.
Just one cam, but getting at the crank and cam to degree it is not a quick after work job.

So whatcha think of putting the adjustment cam gear on and just moving timing by say a degree and watching the compression change?
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Old 01-15-2008, 08:26 AM
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Just one cam, but getting at the crank and cam to degree it is not a quick after work job.

So whatcha think of putting the adjustment cam gear on and just moving timing by say a degree and watching the compression change?
Using a standard compression tester might not show much change with only 1*. Generally you will pick up more low end by advancing the cam. Personnally if I was messing with it I would try 3* do what ever tests ya want to and drive it around and see if you like the new torque curve. Remember distributor timing changes with cam timing!
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I need an FJ40....
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Cruisers are superior
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  #5  
Old 01-15-2008, 08:33 AM
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Using a standard compression tester might not show much change with only 1*. Generally you will pick up more low end by advancing the cam. Personnally if I was messing with it I would try 3* do what ever tests ya want to and drive it around and see if you like the new torque curve. Remember distributor timing changes with cam timing!
I'm pretty sure I understand the idea of cam timing, but maybe what I'm trying to figure out first is whether or not my compression numbers are this low (the FSM says to expect 171 psi) because of an out-of-time cam or not. My short block warranty expires in about 2 months. Or should I just trust my seat bottom and ignore the actual numbers to large extent?
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Old 01-15-2008, 08:39 AM
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Originally Posted by DaveInDenver View Post
I'm pretty sure I understand the idea of cam timing, but maybe what I'm trying to figure out first is whether or not my compression numbers are this low (the FSM says to expect 171 psi) because of an out-of-time cam or not. My short block warranty expires in about 2 months. Or should I just trust my seat bottom and ignore the actual numbers to large extent?
They do seem low but they are consistent! Even cranking the cam forward to 6* isn't going to get you 40#'s of compression! What kind of oil are you using? Thin synthetics will net lower compression numbers too!
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Cruisers are superior
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  #7  
Old 01-15-2008, 08:56 AM
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They do seem low but they are consistent! Even cranking the cam forward to 6* isn't going to get you 40#'s of compression! What kind of oil are you using? Thin synthetics will net lower compression numbers too!
It's just regular Castrol GTX and I did change it this weekend. The engine has about 5,500 miles on it. I would like to see them at about 160 psi and was thinking that if my cam was off that I'm opening either an intake too late or exhaust too soon and not getting good compression. Just a shot in the dark. I suppose the main question in my mind is whether or not I press Toyota for a new short block or not. I this gnawing feeling that my cylinder hones are glazed or maybe the rings are assembled wrong and no amount of continued hard driving is going to make them better. So I was hoping that being off a couple of degrees on the cam timing might make a 20 psi difference. Just crossing my finger I guess.
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Old 01-15-2008, 09:01 AM
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Originally Posted by DaveInDenver View Post
It's just regular Castrol GTX and I did change it this weekend. The engine has about 5,500 miles on it. I would like to see them at about 160 psi and was thinking that if my cam was off that I'm opening either an intake too late or exhaust too soon and not getting good compression. Just a shot in the dark. I suppose the main question in my mind is whether or not I press Toyota for a new short block or not. I this gnawing feeling that my cylinder hones are glazed or maybe the rings are assembled wrong and no amount of continued hard driving is going to make them better. So I was hoping that being off a couple of degrees on the cam timing might make a 20 psi difference. Just crossing my finger I guess.
I would think a tooth off would seem more obvious. If it was a tooth retarded it would really be a dog and a tooth advanced would probably ping like crazy. What say the mini forums?

Also note: If the cam is aftermarket RV style be careful as they are often ground with advance already! Thats the purpose of the degree wheel!
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Cruisers are superior
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  #9  
Old 01-15-2008, 09:59 AM
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Back to your compression test, I've heard that a wet test typically uses 1 teaspoon of oil, but if that isn't enough, what I have done (for consistency's sake) is to use a pump oiler and see how much '1 pump' squirts into a spoon. If it's consistently less than one tablespoon, then use 1 pump per cylinder in your tests. A pump oiler is a stand-up oil can with a trigger on it and you can fill it with whatever you like.

If your turkey-baster approach delivers an inconsistent quantity of oil, then you might see those wierd jumps in compression. I've also heard and seen that on a 'typical' engine in good condition, a 'wet test' results in a 10 psi jump in compression. If you have ring wear, you should see a higher jump. I use 30 weight oil for my 'wet tests', for what it's worth.

I agree that your compression numbers are low (for a new 22RE in Denver) but I doubt cam timing will have a huge impact on bringing them up. But, I'm no cam timing expert. Since no matter what the cam timing, the valves must be closed at TDC, I don't see how cam timing (unless you have a radical profile) will affect it much.

I have done head gasket jobs last year on two '87 Camry engines (3SFE - 4 cyl), and at 7000' elevation, the engine with 212K miles read (136, 136, 136, 136) and the one with unknown miles (but at least 100K) read (130, 123, 140, 140). Neither engine had any valve or ring work beyond new valve stem seals. I don't think you'll see 171, but I'd like to see 150 across the board, or better. Good luck on this - I know how frustrated you must feel.

Steve
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Old 01-15-2008, 11:11 AM
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Thanks for the thoughts, guys.

Kevin, the mini forums say to put in a 3.4L, bob the bed and do a SAS, otherwise you're just wasting your time. ;-)

I definitely think regarding the compression wet/dry that there's inconsistency with the amount of oil and that light bulb went off last night. Which sent me down the road that maybe the rings are in fact alright. Reading a bit more it seems that the amount of oil that it takes to seal the rings is very small and so using the #1 numbers might indicates that things are really not too bad ring-wise. Also putting too much into the chamber can easily give a false high number, apparently. I definitely think my "true" wet number is somewhere around 5 to 10 psi higher than the dry measurement because of the test operator's mistakes...

I think the reason (correct me if I'm wrong guys) that cam timing affects compression isn't that the valves aren't closed at TDC, but that the intake or exhaust open a little off in the cycle and I don't get a complete intake or early exhaust. So being off a tooth (or advanced or retarded too much with an adjustable cam gear) probably won't be noticed with the valve cover off and a feeler under the rockers, but as the engine is turning. If that's the case, then like you say a 10 or 15 psi difference would be huge in how well my engine is breaking in.

Like I say, I don't mind experimenting and tweaking things. The engine is running not too bad and it passed emissions last October and I've got it running even a little better since. I'm just up against that 12 month warranty with Toyota for the short block. I'd rather not pull the engine and deal with a Toyota warranty guy just to find that my compression numbers are low because I put the timing chain off a tooth or because the non-Toyota cam has it's lobe center off by a degree or something.
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