96 compression numbers.
Thread Starter
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Tourer
Joined: Jun 2012
Posts: 351
Likes: 27
From: in a place with no Drama.
96 compression numbers.
Bike has 70k miles, top end sounds a lil sloppy. I did a compression test.
160 rear / 165 front. front, cams.are S&S 551
Are those considered acceptable numbers?
TIA.
160 rear / 165 front. front, cams.are S&S 551
Are those considered acceptable numbers?
TIA.
Road Master
Joined: Jun 2019
Posts: 952
Likes: 528
From: Richmond TX
A spread of 5 psi isn't bad, and 160 psi is certainly enough for the motor to run. Given the impact of intake valve timing and other variables, someone who has measured compression on a 96 with your cams will have to weigh in with what's expected. Are you at or near the expected numbers for a sound motor with 551's? Maybe down 20 psi? Hopefully somebody with your cams has some insight.
HDF Community Team
Joined: Jun 2006
Posts: 12,763
Likes: 2,597
From: san antonio
As Since 1968 says, 5psi variance between cylinders is OK. However, the 551 cam has a very early intake close which pushes CCP up from stock. If the motor is a Stage II, cam upgrade only, i.e., no head work, no domed pistons, no head decking, OEM head gasket, etc. CCP should be about 185psi at sea level. Use the Big Boyz compression calculator and adust for sea level to see how 160-165 compares.
Thread Starter
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Tourer
Joined: Jun 2012
Posts: 351
Likes: 27
From: in a place with no Drama.
As Since 1968 says, 5psi variance between cylinders is OK. However, the 551 cam has a very early intake close which pushes CCP up from stock. If the motor is a Stage II, cam upgrade only, i.e., no head work, no domed pistons, no head decking, OEM head gasket, etc. CCP should be about 185psi at sea level. Use the Big Boyz compression calculator and adust for sea level to see how 160-165 compares.
Road Captain
Joined: Oct 2020
Posts: 518
Likes: 593
From: Central Iowa
I put very little stock in compression test readings. A compression test can be a useful diagnostic tool in certain circumstances but mostly for comparison to other cylinders or to find massive loss of compression. As an indicator of engine wear, power, or overall engine health it's a pretty useless test as there are way to many variables that are next to impossible to account for ie; during the test what was battery voltage when cranking? How much current was the starter drawing? What was the engine temperature? What was the oil temperature ? What was the ambient temperature? What was the barometric pressure? What's your elevation? How much oil was on the cylinder walls? What position were the piston rings in? Etcetera......
What exactly do you mean when you say the top end sounds a little sloppy?
What exactly do you mean when you say the top end sounds a little sloppy?
Thread Starter
|
Tourer
Joined: Jun 2012
Posts: 351
Likes: 27
From: in a place with no Drama.
I put very little stock in compression test readings. A compression test can be a useful diagnostic tool in certain circumstances but mostly for comparison to other cylinders or to find massive loss of compression. As an indicator of engine wear, power, or overall engine health it's a pretty useless test as there are way to many variables that are next to impossible to account for ie; during the test what was battery voltage when cranking? How much current was the starter drawing? What was the engine temperature? What was the oil temperature ? What was the ambient temperature? What was the barometric pressure? What's your elevation? How much oil was on the cylinder walls? What position were the piston rings in? Etcetera......
What exactly do you mean when you say the top end sounds a little sloppy?
What exactly do you mean when you say the top end sounds a little sloppy?
Seems noisier than usual at idle and when riding around.
Road Master
Joined: Jun 2019
Posts: 952
Likes: 528
From: Richmond TX
A leakdown test would tell you a lot more about the engine's condition. It might help you decide whether to overhaul or just ride.
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Road Master
Joined: Jun 2019
Posts: 952
Likes: 528
From: Richmond TX
A couple of other things to look into. There's a guy active on here that sells a product to address excess rocker noise. Dang, my memory.... something like Rocker Lockers? Seems pretty helpful on twin cams.
And, you might have a lifter on the way out. Your bike has cams installed so probably has adjustable lifters, meaning it wouldn't take too much work to change lifters or at least pull them and inspect them.
And, you might have a lifter on the way out. Your bike has cams installed so probably has adjustable lifters, meaning it wouldn't take too much work to change lifters or at least pull them and inspect them.
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Thread Starter
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Tourer
Joined: Jun 2012
Posts: 351
Likes: 27
From: in a place with no Drama.
A couple of other things to look into. There's a guy active on here that sells a product to address excess rocker noise. Dang, my memory.... something like Rocker Lockers? Seems pretty helpful on twin cams.
And, you might have a lifter on the way out. Your bike has cams installed so probably has adjustable lifters, meaning it wouldn't take too much work to change lifters or at least pull them and inspect them.
And, you might have a lifter on the way out. Your bike has cams installed so probably has adjustable lifters, meaning it wouldn't take too much work to change lifters or at least pull them and inspect them.
HDF Community Team
Joined: Jun 2006
Posts: 12,763
Likes: 2,597
From: san antonio
OP has never let us know what lifers were installed and we have asssumed adjustable push rods but the OP has not confirmed that either. If adjustable push rods are installed, which ones and how deep was preload set? Were they adjusted at TDC on the compressin stroke? Let's get the basics our of the way before jumping to compression and leak down tests.