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I've been tinkering with my bike a bit more and noticed some…

Good afternoon. I've been tinkering...
Good afternoon. I've been tinkering with my bike a bit more and noticed some bad compression problems. My front compression is reading at 140 while the rear is only 85. The bike hasn't been run for awhile so I'm hoping it may just be build up in the engine that I can clean but I'm worried it's the Piston rings or the valve seats
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Answered in 1 hour by:
11/17/2017
Steve
Steve, Motorcycle Mechanic
Category: Motorcycle
Satisfied Customers: 7,278
Experience: 30+ yrs. experience, MMI, HD technician, HD early, engine rebuild/performance, bike builder, kit bike program manager, CCI 2001-2004
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you will have to perform a leak down test to determine the cause of the low compression.

most shops can do that. it does require a special "leak down" tester.

but my experience tells me the bike was parked with a bad cylinder.

Steve

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Customer reply replied 9 months ago
I have the equipment to perform a leakdown I just have no idea what I'm looking for

here's a link for reference http://www.gregsengine.com/cylinder-leakdown-testing.html

- place the rear cylinder at TDC/ compression.

- you should consider placing the transmission in gear and engaging the rear brake to hold it there, but you should shoot for as close to TDC as you can.

- install the leak down tester, connect to a compressor and turn it on.

- the gauge will indicate the degree of leak down.

- if the leakage is b y the rings, you'll hear air at the crankcase breather opening.

- if the leak is by a valve, you'll hear air in the intake for a leaky intake valve and in the exhaust pipe for a leaky exhaust valve.

Steve

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Customer reply replied 9 months ago
Appreciated. And this would most likely be because it's been sitting with no attention and hasn't been turned over in years ?

no. not unless it rusted while setting.

as I stated, I suspect it was parked with a bad cylinder.

Steve

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Customer reply replied 9 months ago
I took it to a shop while it was having starting and running problems and they said the valves needed adjusting and possibly need to be lapped. I will try the leakdown test and see what part of the engine is not holding compression

let me know if you need more help.

if not, please accept my answer.

thank you,

Steve

Steve
Steve, Motorcycle Mechanic
Category: Motorcycle
Satisfied Customers: 7,278
Experience: 30+ yrs. experience, MMI, HD technician, HD early, engine rebuild/performance, bike builder, kit bike program manager, CCI 2001-2004
Verified
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