What percentage of leakdown in a 80 hour motor ?
08-10-2002, 03:23 PM
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What percentage of leakdown in a 80 hour motor ?
I'm just doing some routine maintenance and decide to leakdown the motor.
I first warmed it up since I planned on checking valve lash.
I went thru the lash and found one that went from .020 to .024 and the lock nut wasn't loose. I tightened it up and rolled the motor over several times and it stayed tight .... should I be concerned that the lifter (solid roller) is going away ?
Well back to the leakdown question.
#1 10%
#2 35%
#3 20%
#4 15%
#5 20%
#6 25%
#7 25%
#8 15%
Why are they some drastically different ? All the plugs looked good except for Cyl. # 2 that one was black. This motor runs fine. With these percentages I feel that it's time to freshen it up.
What are your guys' opinions.
This motor has 80 hours but it's been thru 3 poker runs and has been run REAL hard .
I first warmed it up since I planned on checking valve lash.
I went thru the lash and found one that went from .020 to .024 and the lock nut wasn't loose. I tightened it up and rolled the motor over several times and it stayed tight .... should I be concerned that the lifter (solid roller) is going away ?
Well back to the leakdown question.
#1 10%
#2 35%
#3 20%
#4 15%
#5 20%
#6 25%
#7 25%
#8 15%
Why are they some drastically different ? All the plugs looked good except for Cyl. # 2 that one was black. This motor runs fine. With these percentages I feel that it's time to freshen it up.
What are your guys' opinions.
This motor has 80 hours but it's been thru 3 poker runs and has been run REAL hard .
08-10-2002, 08:56 PM
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Hi 26 Scarab,
When you did your leakdown test were you able to listen to where the air was escaping from? Cylinder #2 would intially indicate (because of the black spark plug) that you're either running rich or bypassing oil, which would point to a bad ring or glazed cylinder wall. 80 hours isn't alot, but if most of those were near WOT, and there's a chance you were floating valves or hitting your rev limiter often, more than likely your loss of pressure is in the valve seats. A rather crude way to check if it's the rings, aside from sound, is to spray oil (30 wt) into the cylinder via the spark plug hole and then do your leak down. If the pressure is maintained after that, then you pretty much know the rings are the problem.
Good luck!
When you did your leakdown test were you able to listen to where the air was escaping from? Cylinder #2 would intially indicate (because of the black spark plug) that you're either running rich or bypassing oil, which would point to a bad ring or glazed cylinder wall. 80 hours isn't alot, but if most of those were near WOT, and there's a chance you were floating valves or hitting your rev limiter often, more than likely your loss of pressure is in the valve seats. A rather crude way to check if it's the rings, aside from sound, is to spray oil (30 wt) into the cylinder via the spark plug hole and then do your leak down. If the pressure is maintained after that, then you pretty much know the rings are the problem.
Good luck!
08-11-2002, 03:06 AM
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Wette vette ,
I run the lash at .020 intake and .022 exhaust,
SteveDavid,
I know I could have diagnosed this a little better than I did , As you suggested.
I feel that it is in the valve job, yes I do run the motor hard but I know It isn't floating the valves or running on the limiter. But my cylinder head guy is into funky valve jobs that make HP but should be used in a race only application. They might not last in a pleasure boating world .
The wierd thing is , this motor has run the best ever this year I (with some tuning) the boat picked up 2 MPH this season. For a motor that leaks down that bad it doesn't make sense.
I will probably run it the rest of the season and then go thru it.
I run the lash at .020 intake and .022 exhaust,
SteveDavid,
I know I could have diagnosed this a little better than I did , As you suggested.
I feel that it is in the valve job, yes I do run the motor hard but I know It isn't floating the valves or running on the limiter. But my cylinder head guy is into funky valve jobs that make HP but should be used in a race only application. They might not last in a pleasure boating world .
The wierd thing is , this motor has run the best ever this year I (with some tuning) the boat picked up 2 MPH this season. For a motor that leaks down that bad it doesn't make sense.
I will probably run it the rest of the season and then go thru it.
08-11-2002, 09:10 AM
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26, We had a similar condition on our small block Baja. The compression was good and the motor was running great. A friend was showing us his new leakdown testor and the numbers were horrible. We stressed it for a while and decided to leave it alone. That motor is still in the boat and running strong 5 seasons later and we have since added nitrous. Maybe we didn't know how to read the guages or something. I like to check compression first and then do a leakdown on the cyl. that has bad compression. Have you ever used a compression testor to help in setting valve lash? If you alter the lash .002 to .003 you can see cyl pressure changes. Higher cranking generally means cleaner idle and more low / mid power. Lower cranking pressures mean higher top end dynamic compression and power. Just something else to try. You may find a MPH or two and you may not. Hope your motor is OK. Are you getting any blowby?
08-11-2002, 10:12 PM
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Well I guess the leak down percentages are a moot point 
I had the boat out today and broke it just as we were coming in.
The lifter that loosened up ended up breaking. If I would have just pulled the intake I would have seen that it was going bad. I think I thru with solid roller cams. I'm going to do some research and see what I can do with a hydralic roller. Hopefully I won't loose too much power.
I had the boat out today and broke it just as we were coming in.
The lifter that loosened up ended up breaking. If I would have just pulled the intake I would have seen that it was going bad. I think I thru with solid roller cams. I'm going to do some research and see what I can do with a hydralic roller. Hopefully I won't loose too much power.
08-12-2002, 02:25 AM
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26 Scarab,
Sorry about the engine failure. You won't lose that much going to a hydraulic Roller. On a dyno the HP difference might be measurable for both HP and Torque, but if your lift, C/L and duration are the same, you'll enjoy about the same performance AND not have to worry about continuous valve setting.
Good luck!
Steve
Sorry about the engine failure. You won't lose that much going to a hydraulic Roller. On a dyno the HP difference might be measurable for both HP and Torque, but if your lift, C/L and duration are the same, you'll enjoy about the same performance AND not have to worry about continuous valve setting.
Good luck!
Steve
