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Posted by 03 Cobra (Member # 8165) on :
 
This is word for word that is on my recipe from ford. No techs were there for me to ask any questions.

Compression in Cylinders. Check and advise leak down check and found

(leak down test)
Cylinder %
1 = 5%
2 = 18%
3 = 5%
4 = 5%
5 = 5%
6 = 20%
7 = 24%
8 = 5%

Cylinders 2,6 & 7 leaking Passed the exhaust valves Did not hear any leakage in the block or intake, Recommend installing new Head

(RECAP This is the compression NOT DONE BY FORD nor is it on the recipe)

Cylinder PSI

1 = 148
2 = 148
3 = 148
4 = 138
5 = 148
6 = 115
7 = 125
8 = 125

Any input would be great
 
Posted by turbo50 (Member # 6700) on :
 
I would have the same done at another facility or do it yourself, but if those numbers are correct start weighing your options.

Looks like AED does some nice work, tho I cannot vouch for them personally.

Dan
 
Posted by hidnn.o.s. (Member # 1219) on :
 
Being you set up a leak down I'm assuming there is concern. Those numbers would confirm reason to be concerned. What is your question? Are you asking what you need to do, or if the numbers are real?
 
Posted by 93PONY (Member # 60) on :
 
Hard to do a leakdown on these motors since there's no way to easily verify the valves are closed.

However, it's a known issue that the drivers head (cyl 5-8) wear out the guides faster, will not seal as well, & therefore have less compression & more 'leak'.

I'd say that Ford screwed up on the #2 cylinder leak down test. (agian, VERY difficult to do on one of these motors) The proper way to do a leakdown is to remove all the rocker arms & perform the test at varying points of piston travel. I guarantee Ford did not do this....it's WAY too time consuming.

Normally, we just go off compression #'s.

That being the case, you're low on all 8 cylinders. If there's no oil in the blower inlet (behind the TB) that tells me it's probably not the bottom end. Which leaves the valves being the leaking components. To fix this a valvejob is necessary....or new heads..... Depends on if you have overheated the motor at any time & have the 'head tick'. To fix a head with the 'head tick', it's necessary to replace all the valve seats as well as any guide repair when doing a valvejob.

'Head tick' is loose valve seats. Loose valve seats will eventually fail & cause massive engine damage.
 
Posted by 2stangs69-91 (Member # 1951) on :
 
why can't you do a leak down at TDC of the compresion stroke? I know of zero gass engines that have valves open then? It should be legit. Plus you need to do it on a warmed up engine which makes it difficult. I have seen engines with 20% leakdown on the test still run strong. Why did you take it in is it running poorly?
If your compresion test is acurate it looks like 93pony has some good info for you. You can't go buy his numbers(as for being a high of 148) if it isn't the gauge you are familure with. but you can go of the difference in compresion with the same gauge which shows a big issue with cyl #6 and low readings on #7,and #8
 
Posted by Elliott (Member # 7471) on :
 
quote:
Originally posted by 2stangs69-91:
why can't you do a leak down at TDC of the compresion stroke? I know of zero gass engines that have valves open then? It should be legit. Plus you need to do it on a warmed up engine which makes it difficult. I have seen engines with 20% leakdown on the test still run strong. Why did you take it in is it running poorly?
If your compresion test is acurate it looks like 93pony has some good info for you. You can't go buy his numbers(as for being a high of 148) if it isn't the gauge you are familure with. but you can go of the difference in compresion with the same gauge which shows a big issue with cyl #6 and low readings on #7,and #8
its difficult on an overhead compared to a pushrod motor... pushrod motor you can pop the valve cover and undo the rockers so you know for a fact that the valves are closed.

How many people do you know wanna just pop off the valve covers then loosen if not undo the cam hold down (girdle)then pull the rockers. to ensure the valves are shut.. kind hard to do on a DOHC while its in the car.

Even if you get it on TDC, you still have to lock down the crank from moving (sometimes the piston moves when you put the air pressure in). So lets say you lock the flywheel in place to keep the crank rotating.. great... but again how do you verify that the valves are both shut.

That and its a 4valve motor.. and it only takes 1 valve to cause an issue.
 
Posted by 2stangs69-91 (Member # 1951) on :
 
because I am a profesional Mech with 23 years exp. And I have done 100's of leak down test lol thats how I know. Yes there are 4 valves but they also open and close just like a 2 valve pushrod motor(they just go about it differntly). They can not be open at TDC compresion and if the piston moves put it back. Plus if you have ever done a lekadown test you can here the air change when the piston moves. You guy's are killing me lol and yes I have done leakdown test on plenty of 4 valve motors.

[ March 05, 2008, 01:35 PM: Message edited by: 2stangs69-91 ]
 
Posted by 93PONY (Member # 60) on :
 
The lash adjusters on 2 & 4V motors tend to 'pump up' with oil & hold the valves open on the base circle of the camshaft. From the factory, there seems to be an excessive amount of preload in the lash adjusters. I've assembled heads with used lash adjusters that have been sitting in oil for months....& even then when bolting down the cams on the base circle, the lash adjusters do not bleed off & the valves hang open.

Plus, it's hard to tell when the piston is at TDC since there's no timing marks aside from the 10 BTDC mark on the front cover.

& even then, I too have seen tons of leak out of motors that ran excellent with zero issues. Rings seal MUCH better with pressure behind them.
 
Posted by 2stangs69-91 (Member # 1951) on :
 
I never do a leak down on a non running engine. One that is not in service. Rings are not seated in correctly maybe the cyl has lost some oil and its seal. It has to be done on a running, warm engine to be effective. Plus I usualy only do a leakdown test after a compresion test has shown low to determin the area of the compresion leak. I mentioned above I have seen engines with 20% and over leakdown run great. I used to build my 427 FE's so lose it would scare you to do a cold leakdown on them lol. Everything wasn't correct on them untill they were warmed up and buzzing 7 grand. [Wink]
 
Posted by Yaterstang (Member # 7659) on :
 
quote:
Originally posted by 93PONY:
To fix this a valvejob is necessary....or new heads..... Depends on if you have overheated the motor at any time & have the 'head tick'. To fix a head with the 'head tick', it's necessary to replace all the valve seats as well as any guide repair when doing a valvejob.

'Head tick' is loose valve seats. Loose valve seats will eventually fail & cause massive engine damage. [/QB]
So is the verdict, to get a new valvejob or new heads then right?
 
Posted by 2stangs69-91 (Member # 1951) on :
 
you have to do a wet compresion test(add oil see how much the readings change)if the stay simular then yank the heads and inspect them.
 
Posted by 93PONY (Member # 60) on :
 
The best readings we get from these motors on a compression test is straight off the dyno after a clean WOT pull (typically 10-15psi higher). Next best is after driving some distance. Worst is when the motor is cold.

Since I did the compression test..... I know it was repeated & done on a warm motor that had driven quite a ways to get to me.

I also know what the readings of fresh (stock) 03 Cobra motors show on this same compression guage. (170-180psi)

Given this info.....I suggest the heads are removed & given a valvejob/new guides or guide-liners. If time is an issue, replacing the heads with new ford units is another option.

Replacing the heads is a weekend job, getting the machine shop to get their ass in gear & do a valvejob can take weeks.

Or....since it doesn't have the 'head tick', drive it till it starts blowing smoke on startup (which could take years depending on how hard/much the car is driven).
 
Posted by 2stangs69-91 (Member # 1951) on :
 
well there you go. Since all 8 are down on a known good gauge. I would have AED yank the heads and fix it for you. [Wink]
 




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