Leak down test
Seasoned HDF Member
Joined: Oct 2015
Posts: 13,526
Likes: 34,688
From: Pine Flat Dam/South Bay Area, CA
If the OP has an aftermarket cam in the bike, 147 psi isn't a problem.
Seasoned HDF Member
Joined: Mar 2010
Posts: 38,587
Likes: 6,435
From: Honah Lee
The manual for it like my TCb 04 says 90 minimum.
That's a warm engine, with throttle wide open .
At 34,529 mine had 149 and 139. Most TCs in those years had moderate compression ratios 8.9-1 and run on mid grade or even regular at sea level flat lands.
That's pretty typical across the model line except the 1200 sporty at 9.7-1
That's a warm engine, with throttle wide open .
At 34,529 mine had 149 and 139. Most TCs in those years had moderate compression ratios 8.9-1 and run on mid grade or even regular at sea level flat lands.
That's pretty typical across the model line except the 1200 sporty at 9.7-1
Last edited by Jackie Paper; Apr 9, 2025 at 02:40 PM.
Seasoned HDF Member
Joined: May 2008
Posts: 21,173
Likes: 12,740
From: South Carolina
Your compression numbers are fine, no need to do a leakdown test.
A leakdown test only shows the leakage with the piston in one spot, it is more of a troubleshooting tool that an engine health tool.
The reason the piston is being forced down when you pressurize the cylinder is because the piston is not at the top of the stroke, it doesn`t have to be far off TDC for this to happen (on an airplane you can have someone hang on to the prop
).
If compression test shows low compression, a leakdown test is a good way to see where compression is being lost, but this is more useful on aircraft engines, where there are things that can be done to solve the issue without very expensive engine disassembly (on a piston aircraft engine the valves can be lapped with the heads still installed).
Another thing to keep in mind is that a compression test or leakdown test may not be telling you how the compression is when the engine is actually running.
If the engine is performing well and not consuming oil, there is no reason to look for problems.
A leakdown test only shows the leakage with the piston in one spot, it is more of a troubleshooting tool that an engine health tool.
The reason the piston is being forced down when you pressurize the cylinder is because the piston is not at the top of the stroke, it doesn`t have to be far off TDC for this to happen (on an airplane you can have someone hang on to the prop
).If compression test shows low compression, a leakdown test is a good way to see where compression is being lost, but this is more useful on aircraft engines, where there are things that can be done to solve the issue without very expensive engine disassembly (on a piston aircraft engine the valves can be lapped with the heads still installed).
Another thing to keep in mind is that a compression test or leakdown test may not be telling you how the compression is when the engine is actually running.
If the engine is performing well and not consuming oil, there is no reason to look for problems.
Last edited by Dan89FLSTC; Apr 9, 2025 at 03:07 PM.
HDF Community Team
Joined: Jun 2006
Posts: 12,776
Likes: 2,607
From: san antonio
Not saying the OPs compression numbers are a problem; just saying I would have expected 155-160 at the "near new" mileage.
Last edited by djl; Apr 9, 2025 at 04:35 PM.
Thanks for the responses. I'm working on this bike because the client says that he was having throttle response issues and that he heard a valve noise. He also wanted me to go through the rest of the bike as well. I did a test ride and didn't notice anything other than he had no rear brake. The bike is all stock including the original tires and has 1603 miles. The bike wasn't stored to good, as there is rust all over but not too bad, just needs a good cleaning.
As of now, the carb is being cleaned and rebuilt. I did the compression and leakdown tests to rule out the valve noise. Took the bike for a chilly ride and nothing really stood out. Clutch adjustment w/fluid change and the rear brake needed a fluid flush. It's a solid bike just needs some TLC.
I appreciate all the responses, I was just confused on the rear cylinder leak down test.
Ride safe!
As of now, the carb is being cleaned and rebuilt. I did the compression and leakdown tests to rule out the valve noise. Took the bike for a chilly ride and nothing really stood out. Clutch adjustment w/fluid change and the rear brake needed a fluid flush. It's a solid bike just needs some TLC.
I appreciate all the responses, I was just confused on the rear cylinder leak down test.
Ride safe!
My leak down tester has PSI breakdown chart for testing at 100, 90, and 80 PSI. I did 90 so I wouldn't have to change the regulator on my compressor cause its already set up for my pneumatic tools.
Ride safe!
Ride safe!
Seasoned HDF Member
Joined: Mar 2010
Posts: 38,587
Likes: 6,435
From: Honah Lee
Never seen a leak down set like you have. Does the instructions interpret that reading you got as 3%?
HD Forum Stories
The Best of Harley-Davidson for Lifelong Riders
7 Surprising Harley-Davidson Products that Are Not Motorcycles
Verdad Gallardo
8 Best Harley-Davidson Motorcycles Ever
Pouria Savadkouei
10 Worst Harley-Davidson Motorcycles Ever
Pouria Savadkouei
Killer Custom's Jail Break Is The Breakout That Refused to Blend In
Verdad Gallardo
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Verdad Gallardo
Harley-Davidson Reveals Super Cool Cafe Racer Concept
Verdad Gallardo
Engraved Rebellion: Inside Bundnerbike's Glam Rock II
Verdad Gallardo
10 Motorcycles You Should Never Buy
Joe Kucinski
10 Things Harley-Davidson Needs to Fix in 2026
Verdad Gallardo
I only rode in the immediate neighborhood, but I did tell him to replace the tires.
Ride safe!
Ride safe!
