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Discussion Starter #1
I was reading the posts from ‘PACE’ about the problems with his bike and saw a comment saying that a ‘leakdown test isn’t important and don’t bother with it.

I’m here to disagree and would like to relate something that happened to me and maybe it could help someone else.

These are the facts as they occurred to me first hand.
I worked at Spinetti’s Bike Shop in Jackson, Ca. We were authorized Honda, Suzuki and Kawasaki dealership.

This occurred in the 1990’s although I don’t remember the exact date. I had to work on a GL1200. The work order said that it ‘misses on 1 or more cylinders on acceleration and idles rough....

has been sitting, needs new battery.’ The RO also said ‘shop in Sac cleaned carbs and tune up- no help’

So I have to interpret what is needed so first thing is jump it with my test battery. There could be more than just needing a battery and I won’t charge him for a battery if that’s not the problem.

I get the engine to start and the RO is right ... runs rough at idle and a dry rev doesn’t sound that great. So first things first... compression test and leakdown test.

Honda has pounded those 2 tests into our brains at every Honda class I’ve been to.

So compression shows a little low on 3 cylinders and about 20 psi low on 1 cylinder. Not bad.., could be worse.

Leakdown shows 10% leakage on 2 cylinders and 70%+ leakage on 2 cylinders.

Needs new valves? I had the service manager contact the customer for authorization to tear down.

I know this is long but the point is the engine needed none of what had been done by the shop in Sacramento and he’d wasted his money.

I got the engine fixed and it purred like new.... because of the leakdown test.
This story is true!
 

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If it were me I would have isolated the bad cylinders by shorting plug wires to ground. Next I would have checked for thumb compression.If I saw 2 adjacent cylinders bad my first guess would be head gasket. Next That would be enough to know the engine has to come apart somewhat. If I really cared to go farther I could blow compressed air in the bad cylinder and see where it escapes.
Remember that in the post they were trying to diagnose a cracked cylinder head. Lots of better choices than a leak down test.
As for your example I guess I would say whatever works for you. You got her going and that is what counts. Lots of ways to skin a cat. :) Not sure why Honda would want compression and leak down tests on the same bike???? Worked as a heavy duty diesel mechanic for long time. Can't hardly use a compression tester on them. No spark plug hole. :p
 

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Discussion Starter #3
Granted it’s hard to do a compression test with no spark plug hole-LOL
The compression test on 4 stroke engines shows cylinder wear, lower cylinder seizure problem and wear in the cylinder.
Since the leakdown test only shows what leaks when the piston is at TDC and both valves are closed. We used both tests in conjunction as a diagnostic tool. Those are my reasons for using both tests.
 

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Never had use for a leakdown test except to find out where the leakage was.
 
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It aint rocket science
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In one of the Ford dealerships that I worked in I was the engine guy, anything with excessive blow-by or a skip/knock in the engine that was not ignition related came to me. Compression test always done after isolating which cylinder was causing the skip. Then the valve cover came off to watch the rocker-valve train movement while cranking over. Then on to the poor man leak down test by injecting shop air into the offending cylinder after the rockers were backed off. Oil pressure test also when needed. The more information you have prior to a tear down the better off one is.:cool:
 

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Discussion Starter #6
Never had use for a leakdown test except to find out where the leakage was.
We had both tests required at every Honda seminar or tech class and since I did see where a comp test was on the low side of specs but the leakdown test showed excessive percentage
I came to believe in both test results before the final diagnosis. Hey... as long as it gets fixed, eh?
 

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Pulling the spark plugs can tell a few things. A compression test only adds a little time.

I only do a compression test if I am looking for something. The leak down test shows what is causing the low compression.

I only put air into the cylinder to hear where its coming out. I listen to exhaust, intake and oil filler if its blowing by the rings. I have no gauge that reads in %.

I don't like to fix something until I am sure what is wrong. No throwing parts at it, because if its not the fix, it comes out of my pocket.

David
 

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You can compression check diesels, pull the injector or, if fitted, glow plug but the gauge reads a lot higher
 

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I was reading the posts from ‘PACE’ about the problems with his bike and saw a comment saying that a ‘leakdown test isn’t important and don’t bother with it.

I’m here to disagree and would like to relate something that happened to me and maybe it could help someone else.

These are the facts as they occurred to me first hand.
I worked at Spinetti’s Bike Shop in Jackson, Ca. We were authorized Honda, Suzuki and Kawasaki dealership.

This occurred in the 1990’s although I don’t remember the exact date. I had to work on a GL1200. The work order said that it ‘misses on 1 or more cylinders on acceleration and idles rough....

has been sitting, needs new battery.’ The RO also said ‘shop in Sac cleaned carbs and tune up- no help’

So I have to interpret what is needed so first thing is jump it with my test battery. There could be more than just needing a battery and I won’t charge him for a battery if that’s not the problem.

I get the engine to start and the RO is right ... runs rough at idle and a dry rev doesn’t sound that great. So first things first... compression test and leakdown test.

Honda has pounded those 2 tests into our brains at every Honda class I’ve been to.

So compression shows a little low on 3 cylinders and about 20 psi low on 1 cylinder. Not bad.., could be worse.

Leakdown shows 10% leakage on 2 cylinders and 70%+ leakage on 2 cylinders.

Needs new valves? I had the service manager contact the customer for authorization to tear down.

I know this is long but the point is the engine needed none of what had been done by the shop in Sacramento and he’d wasted his money.

I got the engine fixed and it purred like new.... because of the leakdown test.
This story is true!
I could not agree more.
As a registered VW and ASE master tech, back-in-the-day. You didn’t do any warranty engine work without ALL the documentation (meaning before and after readings, confirming proper repair). Or you paid for the repairs yourself. Almost!! You didn’t get any pay for the work (flat rate). Anyway, a real cylinder leak down test (with read outs) is vital information. (y)
 

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Each test has benefit(s). Compression test to check for cylinder integrity - rings/valves. Leak down test to check where the leaks are that affect compression. Older Gold Wings glazing of the cylinders, exhaust valves are good possibilities for low compression. Only two choices with an issue/problem, accept it or fix it.

These tests have merit along with voltmeters, pressure gauges and such. Need to see consistency, and note changes. Inexpensive voltmeters are notorious for being out of range, but if the readout is constant/consistent all's good. It's when it changes you need to look at what is happening. As with all readings, once the issue is found, it's whether you are going to resolve the issue. Back in the day at my father's garage, always mentioned that if you do the top end of an engine should do the bottom end, keeps everything balanced and wearing the same. Making one part/system stronger can play havoc with the other reciprocal end. Just a thought or two.

Cheers
 

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When working on race engines, we ran a leakdown after every race. Anything over 5% it comes apart to correct. Can't recall ever doing a compression test, except the occasional thumb test when you know something's really gone south. You can also do a leakdown at BDC, great for finding split cylinder walls.
 
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