34 replies to this topic

[Chris D.]

Something isn't adding up about the original poster's numbers,.  Forget the piston stop for a minute, just put a long 3/8" extension down the #1 hole, and convince yourself where TRUE TDC is.  Make a mark on the pulley halfway between where the extension starts to go down on either side of TDC. 

 

I plan on doing exactly this.  I will compare it to stock timing marks and let everyone know what I find.

 

Also, it turns out I misinterpreted the leakdown reading on the Longacre gauge.   My air tank bled down below 100 psi and I did what I thought was some correct math to get the leakdown numbers.   So, after contacting Longacre, they gave me the low down.   I posted their response in quotes below.   Using their calculation method, my numbers would be:

 

Cylinder 1 = 25 %

Cylinder 2 = 19 %

Cylinder 3 = 8 %

Cylinder 4 = 33 %

 

Still crappy, but a little bit better. 

 

"The % leak down IS closely related to the input pressure. 100 psi input is

the standard. If someone uses less than 100 psi - for example 90 psi - he

will need to use the ratio of 100 to his pressure x the displayed leak down

-

ie: 90 / 100 = .90 x 14% = 12.6%.

 

The pressure should not be much below 100 as air flow will be different and

affect the leak down. If someone were to use a much lower pressure, say 60

psi, the % gauge would need to be recalibrated to that pressure.

 

As an overview "leak down" is really a relative number and should be used

for comparison of the engine condition over time. It has no real value in

absolute terms"

[Chris D.]

My longacre gauge was not properly calibrated right out of the box.  With 110+ PSI in the compressor and the input gauge adjusted to 100PSI, the right hand gauge (before connecting the gauge to the engine) did not read zero.  It was off by a few PSI.  I sent it to Longacre and they calibrated it and returned it to me.  Nowhere near enough to get the kind of numbers posted, but could be a contributor.  

 

I honestly did not check this Tom, but I will....thanks for the heads up.

[SaulSpeedwell]

Speed,

In response to your comment about BMWs I felt I must comment. My wife has a 335ci convertible with about 80k miles on it. It has had the fuel pump replaced twice, the vvt controller replaced, the camshaft replaced, water pump replaced. I have a Lexus ISF that has 140k miles on it and it has never spent an hour in the dealer's shop. I have been to multiple track days in the Lexus and it just keeps on ticking.

When we bought the BMW Mike told us to be sure and get the extended warrantee. We did, and it has paid for itself

Pat

 

No no no no no NO NO NO NO NO NO NO NO!  (Family Guy donkey impersonation).  You are totally wrong.  German engineering is the best.  It DOES NOT fail.  It only stops working when incompetent people operate it or fail to maintain it ....

 

 ....even though incompetent people can make a Chevy Celebrity run for 150K miles using tools and parts found in their kitchen "junk drawer", what you clearly fail to realize is the superior engineering in BMWs, Audis, and Mercedes spontaneously exploding every 25K miles or so.

 

... and even though every Miata ever built will go 150K miles with nothing but brakes, tires, and fluids ... and can be completely disassembled and parted out on Ebay using 10, 12, 14, 17, and 21mm wrenches,

 

P.S.  I forgot MINIs.  Those spontaneously explode too.

 

P.S.S.  How much you want for that Lexus?  You couldn't GIVE me the BMW

[Chris D.]

Well I just did recheck my TDC mark.   I used an extension in the spark plug hole and very carefully tried to find the mid point between where the extension would rise and fall.   I checked it three times and I guess I got lucky.   TDC is pretty much right on the mark it should be....certainly within +/- 2 degrees.   I will say that the motor has never been torn down.   So, I would suspect the TDC mark was set accurately as it left Mazda several years ago.  Maybe the larger variations come into play on motors that have been rebuilt.   I haven't see how the little plastic timing indicator mounts to the motor.....not sure if there is some slop in the attachment holes that can lead to variation when it is removed and replaced.

 

I will rerun the leakdown test tomorrow and repost.   This time around I plan to slowly move the piston up and down about TDC and see how the leakdown numbers are affected.

[38bfast]

Chris be careful. When you just get off TDC and add the air pressure to the cylinder it is going to want to turn the crank with a lot of torque. So if you have a wrench on the crank pulley it is going to have ALOT of force. Be carful you don't get your hands pinched. Also there is so much force you can actually loosen the big crank bolt.

[Chris D.]

Ok, just got back from the garage....much better results this time around.  The biggest thing I did different was VERY gently and VERY slowly move the crank just a hair past TDC and then back just a hair before TDC after I applied pressure (thanks for the reminder Ralph....I was careful  ).   Doing this had a major effect on the leak down readings.   It was like shutting a trap door.   Each time it jumped down after the movement just before TDC.  Here's what I got:

 

Cylinder 1 = 18% initial, went down to 3% after moving the crank a bit

 

Cylinder 2 = 19% initial, went down to 8%

 

Cylinder 3 = 2% initial, no movement of the crank needed,

 

Cylinder 4 = 22% initial, went down to 6%

 

Another thing I did different this time was to remove the oil filler cap.   So, this time around any leakage I heard was right out of the cap and not the intake.   So, in my first test with the oil cap on, what I heard through the intake must have been really coming thru the rings, into the crankcase, then back up thru the PCV, and then finally back thru the intake?  Removing the cap this time around just allowed the air to escape directly from the crankcase I suppose. 

 

All in all, this has been a cool learning experience.   Thanks to all for the tips and advice! 

[Johnny D]

http://www.youtube.c...h?v=pnVOt2LK2Gg

J~

[38bfast]

Chris those numbers are much better. For Waterford you will not see a change in lap times with addressing the motor. If you plan on doing mid-o you will be giving up about a second + to the top cars.

[MPR22]

No no no no no NO NO NO NO NO NO NO NO!  (Family Guy donkey impersonation).  You are totally wrong.  German engineering is the best.  It DOES NOT fail.  It only stops working when incompetent people operate it or fail to maintain it ....

 

 ....even though incompetent people can make a Chevy Celebrity run for 150K miles using tools and parts found in their kitchen "junk drawer", what you clearly fail to realize is the superior engineering in BMWs, Audis, and Mercedes spontaneously exploding every 25K miles or so.

 

... and even though every Miata ever built will go 150K miles with nothing but brakes, tires, and fluids ... and can be completely disassembled and parted out on Ebay using 10, 12, 14, 17, and 21mm wrenches,

 

P.S.  I forgot MINIs.  Those spontaneously explode too.

 

P.S.S.  How much you want for that Lexus?  You couldn't GIVE me the BMW

What he didn't tell you is that we own a 2001 330 Ci and have found a sure fire way to eliminate the blown head gasket problem. 

 

 

 

Replace it with Ls3.  

[Danny Steyn]

There ya go Chris

As I said in my earlier response - leakdowns of 18-20 wont give you 200 Compression

Glad you got it figured out - way less effort expended now - this is a decent engine with decent leakdown and compression numbers. Not a totally top shelf totally fresh engine, but very decent.

[SaulSpeedwell]

Ok, just got back from the garage....much better results this time around.  The biggest thing I did different was VERY gently and VERY slowly move the crank just a hair past TDC and then back just a hair before TDC after I applied pressure (thanks for the reminder Ralph....I was careful  ).   Doing this had a major effect on the leak down readings.   It was like shutting a trap door.   Each time it jumped down after the movement just before TDC.  Here's what I got:

 

Cylinder 1 = 18% initial, went down to 3% after moving the crank a bit

 

Cylinder 2 = 19% initial, went down to 8%

 

Cylinder 3 = 2% initial, no movement of the crank needed,

 

Cylinder 4 = 22% initial, went down to 6%

 

 

OK, wait wait wait wait wait.  So if all you did was "dither" the pistons slightly to either side of TDC ... and you got 10-20% changes in leakdown ... then the only answer is that oil film or piston ring "slop" is giving you 10-20% differences.  Or the Longacre is BS.  Or leakdown itself is BS, 

 

OK - fine - no big deal.  But if slightly moving things to either side of TDC made those improvements, then what is happening at 6500 rpm? 

 

Bottom line:  Who cares what leakdown is?  Fast is fast, and dyno numbers trump leakdown numbers.   There is no Runoffs for tightest-sealing engine at static TDC? 

[RazerX]

Chris,

 

I haven't seen a lot of the pro engine builders chiming in.  Saul is very knowledgeable.   

 

You should always do the leak down at the same temp, is the engine hot or cold?  Measure your engine against itself with the same gauge always.  If you hearing it from oil filler hole you not only have leaky valves but your valve seals are leaking as well and with that many miles not surprising.  I would do the same procedure after putting down an 1/2 tablespoon of gear oil in the cylinder, let it sit for a min and do the leak down.  That change would attributed to the rings being sealed and theoretically now you are just measuring the valve leakage.  While exhaust valves will gum up first if you zing the engine any of the valves could take the abuse and then leak.  

 

There are several degrees (engine builders chime in here) that valves should be sealed 3 or 4 degrees or each side of the "true" TDC.  You can take the valve cover off and see the who process as well.  It can be very educational and only costs you time to clean up the seal and add RTV back on.   If your leak down numbers are on a knifes edge I would consider a valve job and validate your timing belt has been changed and is setup correctly.  

 

All in all not bad numbers, my 1.6 had very similar numbers and I just did a compression and leak down periodically to see if it going away.   117 HP is fine if you are not a heavy person but if you get 115 HP or lower you need to watch the torque.  Once you are under 100 FT PD of torque you will other cars pull away our of corners.

 

Any my experience for what it is worth.

[RazerX]

Chris,

 

I haven't seen a lot of the pro engine builders chiming in.  Saul is very knowledgeable.   

 

You should always do the leak down at the same temp, is the engine hot or cold?  Measure your engine against itself with the same gauge always.  If you hearing it from oil filler hole you not only have leaky valves but your valve seals are leaking as well and with that many miles not surprising.  I would do the same procedure after putting down an 1/2 tablespoon of gear oil in the cylinder, let it sit for a min and do the leak down.  That change would attributed to the rings being sealed and theoretically now you are just measuring the valve leakage.  While exhaust valves will gum up first if you zing the engine any of the valves could take the abuse and then leak.  

 

There are several degrees (engine builders chime in here) that valves should be sealed 3 or 4 degrees or each side of the "true" TDC.  You can take the valve cover off and see the who process as well.  It can be very educational and only costs you time to clean up the seal and add RTV back on.   If your leak down numbers are on a knifes edge I would consider a valve job and validate your timing belt has been changed and is setup correctly.  

 

All in all not bad numbers, my 1.6 had very similar numbers and I just did a compression and leak down periodically to see if it going away.   117 HP is fine if you are not a heavy person but if you get 115 HP or lower you need to watch the torque.  Once you are under 100 FT PD of torque you will other cars pull away our of corners.

 

Any my experience for what it is worth.

Sorry not leave Danny or others out of the "very knowledgeable" category.   My bad... 

[Chris D.]

To Saul's point, wouldn't the compression test be the most real world check of engine health?   It's a dynamic test, and, last I checked, engines are dynamic.   I would think you'd use the compression test as a first check.   If you see low numbers, then the leak down test can be used to deep dive where the problems are.

[38bfast]

Chris, that is how we do it in my shop. The compression tester is used to see if we need to brake out the leak tester and then a trip on the Dyno. For an engine to be a good race motor all the numbers need to be good. We frequently take out motors that are 4hp down from where they should be. It does not take much to take a motor from a great one to a good one. Many variables all have to be in place. Or one miss shift can kill a great motor.