More 2H compression numbers

[kim]

Today, some friends and I did compression tests on my 86 and 87 2H's.

The 87, with 530,000kms, tested;

1 - 440
2 - 420
3 - 420
4 - 420
5 - 460
6 - 460

and the 86, with 390,000kms, tested;

1 - 520
2 - 520
3 - 490
4 - 490
5 - 490
6 - 490

These seem like very good numbers to me. I didn't have a leak down tester though. All numbers were taken after each vehicle was running for about two minutes from a cold start.

 

[roscoFJ73]

All numbers were taken after each vehicle was running for about two minutes from a cold start.

A good 20 mins of drive time would have been more accurate. I suspect those figures would taper off as the engine gets warmer.
Still,they seem to be fairly healthy

 

[kim]

A good 20 mins of drive time would have been more accurate. I suspect those figures would taper off as the engine gets warmer.
Still,they seem to be fairly healthy

I did the tests on a cool motor for two reasons, the first being that it sucks to crawl on a hot engine when it's stinking hot out and, two, I thought that I would get 'worse' numbers as far as variability between compression numbers when the piston rings weren't tight in the cylinders.

Am I wrong with this line of thinking?

I guess a retest is in order. How much would you expect these compression numbers to drop if the test were on a hot engine?

 

[roscoFJ73]

I did the tests on a cool motor for two reasons, the first being that it sucks to crawl on a hot engine when it's stinking hot out and, two, I thought that I would get 'worse' numbers as far as variability between compression numbers when the piston rings weren't tight in the cylinders.

Am I wrong with this line of thinking?

I guess a retest is in order. How much would you expect these compression numbers to drop if the test were on a hot engine?

The service manual requires most tests and adjustments to be done warm when all the components are fully expanded and the lubricant thinned down to what it should be.
How much they would drop is anyones guess.
Probably not much if the engine is good.

 

[Justcruzin]

Hummm. Am I in the left field here or are those figures waaaaay high??
Says on page 2-10 and 2-11 of the Toyota Factory service manual for 2H engines that compression tests should be done on a warmed up engine and that the standard compression pressure should be 398PSI with a lower limit of 284 PSI. Had mine checked today and numbers were between 390 and 360 PSI for my 230,000 kms engine.

Are those figures too low or... Confusing...

 

[kim]

OK, I did it again on my 87 2H after a one hour drive in the rat race.

1-460
2-440
3-440
4-460
5-470
6-490

Thanks Rosco, hot job.

 

[kim]

Hummm. Am I in the left field here or are those figures waaaaay high??
Says on page 2-10 and 2-11 of the Toyota Factory service manual for 2H engines that compression tests should be done on a warmed up engine and that the standard compression pressure should be 398PSI with a lower limit of 284 PSI. Had mine checked today and numbers were between 390 and 360 PSI for my 230,000 kms engine.

Are those figures too low or... Confusing...

I've read that these numbers are high on another thread. Perhaps there are different compression figures for different 2H's.

 

[Justcruzin]

Kim.

Guess one can't complain about high compression figures, can he?

 

[kim]

Kim.

Guess one can't complain about high compression figures, can he?

I certainly wont complain about the numbers!

However, I do wonder about the 398 psi number in the 1985 FSM.

 

[roscoFJ73]

I've read that these numbers are high on another thread. Perhaps there are different compression figures for different 2H's.

Last time someone had figures like these,they dropped when he tried a different compression tester to what his mechanic was using.
I think that will happen to you too.

But they are not too far apart.
Have you clocked up many of those klms yourself.
Im a little surprised to see the 87 2H figures went up when a warm test was done

 

[kim]

Last time someone had figures like these,they dropped when he tried a different compression tester to what his mechanic was using.
I think that will happen to you too.

But they are not too far apart.
Have you clocked up many of those klms yourself.
Im a little surprised to see the 87 2H figures went up when a warm test was done

I don't have access to another compression tester so I cannot do a double check at the moment. I've put on about the last 150,000kms on this truck. It has always run smooth and 'strong'.

I was surprised that the numbers went up too, average 20 psi across the board, but I'll take it as good news.

 

[kim]

I have been searching around for information on compression numbers for the 2H. I understand that there are sleeved and sleeveless 2H's, I believe the sleeveless began around 86. The FSM we are all referencing is from 1985. My trucks are 86 and 87. I don't know if there are differences expected in compression numbers.

HOwever, I did find this post;

The Toyota FSMs have a few typos, the compression specs on the 2H/12H-T are reversed and the PSI differential is 2.8 where it should read 28, as browndog mentioned. The 3B/13B-T manual specs 427 for 3B which is correct, but it also specs 427 for the 13B-T where it should read 398.
As far as the PSI difference between cylinders goes, no greater than 10% difference seems to be the accepted standard in the diesel engine world.

Sheldon

https://forum.ih8mud.com/newreply.php?do=newreply&p=947045

 

[Tofudebeest]

Are these numbers in PSI? Sounds just wrong. My numbers almost two years ago:

Aussie spec HJ60. Assembly date: 9/81. ~340,000KM.
Compression #s:
1) 380
2) 375
3) 400
4) 390
5) 365
6) 390


And with factory spec at 398, how can you explain compression numbers in the high 400s with no turbo(and then just a few extra pounds, 20 being really high boost)?

 

[kim]

Are these numbers in PSI? Sounds just wrong. My numbers almost two years ago:

Aussie spec HJ60. Assembly date: 9/81. ~340,000KM.
Compression #s:
1) 380
2) 375
3) 400
4) 390
5) 365
6) 390


And with factory spec at 398, how can you explain compression numbers in the high 400s with no turbo(and then just a few extra pounds, 20 being really high boost)?

Yes, PSI. And, I can't explain the high numbers on two different 2H's, with a repeat test on one of them. Now, from what I have been reading, 398psi is NOT the correct compression numbers for the 2H although the 1985 FSM says so. I quoted 70sguy earlier who stated that 398 is for the 12HT and 427 is for the 2H. The 1985 FSM has these reversed. Now, if this is true, my numbers are still high.

I'm thinking that a possible explanation is that there are different compression numbers for different styles of 2H, ie 1980-85 and 1986-1990. I can't find any references to the late 2H compression numbers though.

 

[Tofudebeest]

I know the later 2H was sleeved and had a stiffer block, but I can't see how the compression numbers would be different. John at Radd would know...

John? Can you clear things up?

 

[kim]

Im a little surprised to see the 87 2H figures went up when a warm test was done

I was reading an old thread, Rosco, and found this posted by Crushers in response to your "I guess you would have to do a hot and cold compression test to prove /disprove it.";

a hot engine will always have higher compression readings.
the reason an engine doesn't have the same pwer when cold is because the tolerances are not tight enough.
think of it this way, when idleing an diesel excessivly will lead to washing the walls with diesel and contaminating the oil (granted a tiny amount) themore you idle the more glaze you get on the cylinder walls, if the tolerances where the opposite then the damge would be scoring of the walls (which only happens when low oil pressure or dirt contamination of overheating of the block...)

at least this is my understanding...

https://forum.ih8mud.com/diesel-tech-24-volts-systems/123152-2h-running-cool-any-chance-damage.html

I have just performed a cold, then hot, compression test.

 

[kim]

I know the later 2H was sleeved and had a stiffer block, but I can't see how the compression numbers would be different. John at Radd would know...

John? Can you clear things up?

The 2H's I have are sleeveless.

 

[Tofudebeest]

But what say you about these numbers?


I emailed John to see if he'll weigh in...

 

[Radd Cruisers]

The earlier H and 2H were sleeved, and the later ones were parent bore.

The compression numbers that are in the upper 300 range are on the low side of things.

If the numbers are changing a lot hot and cold - check the valve clearances. There will be changes due to temperature....

Make sure that on VSV shutdown engines that the choke plate is open while testing (it should be by default).
On diaphragm fuel controlled engines, make sure that the throttle plate is wide open.

(note that I didn't read the thread, just the last couple of posts).

~John

 

[Tofudebeest]

Now, from what I have been reading, 398psi is NOT the correct compression numbers for the 2H although the 1985 FSM says so. I quoted 70sguy earlier who stated that 398 is for the 12HT and 427 is for the 2H. The 1985 FSM has these reversed. Now, if this is true, my numbers are still high.

The FSM is right. How could a compressed (that's what a turbo is, and why the MB turbo is called a "kompressor") engine have (factory) compression values LOWER than its nearly identical naturally aspirated predecessor? After all, the primary difference between those motors is merely the piston skirt cooling, and of course the turbo. Same bore and stroke, same displacement. Look at the compression ratios...

The 2H is a 4.0 L (3980 cc) inline 6, 12 valve OHV diesel engine. Bore is 91 mm and stroke is 102 mm, with a compression ratio of 20.7:1. Output is 103 hp (77 kW) at 3500 rpm - later production years 107 hp (80 kW) with 177 ft·lbf (215 N·m) of torque at 2000 rpm.


The 12H-T is a 4.0 L (3980 cc) inline 6, 12 valve OHV turbocharged diesel engine. Bore is 91 mm and stroke is 102 mm, with a compression ratio of 18.6:1. Output is 135 hp (101 kW) at 3500 rpm with 231 ft·lbf (312 N·m of torque at 2000 rpm.

I think somebody's compression readings are in error.