Crappy compression options - Page 2 - Steve Saunders Goldwing Forums

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post #11 of 31 (permalink) Old 01-19-2017, 03:38 PM
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Sorry about the weekend thing. I must have readed it ungood.

Not the first time and won't be the last.

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post #12 of 31 (permalink) Old 01-19-2017, 05:17 PM
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Quote:
Originally Posted by billythegrape View Post
I must be in the twilight zone. Never have I heard of, performed, or seen anyone do a compression test on a warm engine, ever. Probably because it's the wrong way to do it, but I guess this IS the internet, so...

Anyway, my bike is ridden every weekday. Don't know where the weekend came from, as the original post says weekday.

I will adjust the valves and perform another cold compression test, as performing one warm would be useless.

Here's why:

When an engine is warmed up, unless it has just one cylinder, the compressions will vary in cylinders due to uneven heating, physical material distribution, etc. Especially in a carbureted engine. Especially in a 40 year old carbureted engine.

When cold, all the metal shrinks down allowing for a more accurate test of what's really going on with compression. This is why many (not all) engines require the engine to be cold to adjust the valves. This is also why we do leakdown tests on a cold engine.

I have never, EVER heard of anyone in the car business doing compression tests on warm engines because it just isn't done that way. Sorry.
I think you need to spend some time reading a service manual, any service manual on any engine.

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post #13 of 31 (permalink) Old 01-19-2017, 06:33 PM
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I usually stay out of these discussions, but here is my personal opinion as to why it is VERY important for it to be done on a Warm Engine, especially for our Goldwings with horizontal cylinders.

Putting in a dab of oil does almost nothing for sealing the top ring, except along the very bottom of the cylinder on a cold engine.

If the engine is warmed up, then oil has gotten up onto the rings evenly and will seal all the way around the cylinder, this will give the best conditions for testing.

So, a vote for a warm engine here.

Now, going back to the '50s and '60s when my dad taught me to do it on a straight six Plymouth.

"son, get the motor warm, pull the plugs, and then test each cylinder"
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post #14 of 31 (permalink) Old 01-19-2017, 06:44 PM
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On the fence here,the difference might be slight but the same variable on all cylinders,on high performance motors warm would give a closer to actual compression but wing motors aren't really high on compression compared to some other motors,wouldn't oil in cylinders give erroneous readings since the oil ring on the piston would keep oil from the top ring?you have the oil ring,then the wiper ring to get excess off the wall of the cylinder?
After reading more on this,the wet test and dry test should be done together to see if there's a difference in compression.
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post #15 of 31 (permalink) Old 01-20-2017, 06:46 AM
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Never was a mechanic, so probably asking you if you checked compression with a wide open throttle is foolish. But anyways, was the trottle all da way open?

As to hot and cold, I've heard both, but I guess once started, all that matters is warm compression- because it won't get cold while running.?

Valve adjust is a must. Oil can give you hints which way to go.
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post #16 of 31 (permalink) Old 01-20-2017, 07:00 AM
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Gee whizzzz do one cold and then warm and see what different it makes??? yep check the valves..do the test as stated above all plugs out, good battery, throttle wide open. Compression specs for a Gl is 165-170 perfect, 160-165 excellent, 155-160 great, 150-155 good, 145-150 OK, 140 145-still OK..below 140 time for new rings according to the manual(assuming valves and gaskets are good)..but these bikes will run with compression all the way down to 100 or 90..as long as you are mot running 1/4 mile for time. Within 5lbs of each other is needed too!! Try the test with dry cylinder and then add a little oil..if the compression comes up = ring issues if not valve or gasket issues.

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post #17 of 31 (permalink) Old 01-20-2017, 09:50 AM
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Quote:
Originally Posted by billythegrape View Post
I must be in the twilight zone. Never have I heard of, performed, or seen anyone do a compression test on a warm engine, ever. Probably because it's the wrong way to do it, but I guess this IS the internet, so...

Anyway, my bike is ridden every weekday. Don't know where the weekend came from, as the original post says weekday.

I will adjust the valves and perform another cold compression test, as performing one warm would be useless.

Here's why:

When an engine is warmed up, unless it has just one cylinder, the compressions will vary in cylinders due to uneven heating, physical material distribution, etc. Especially in a carbureted engine. Especially in a 40 year old carbureted engine.

When cold, all the metal shrinks down allowing for a more accurate test of what's really going on with compression. This is why many (not all) engines require the engine to be cold to adjust the valves. This is also why we do leakdown tests on a cold engine.

I have never, EVER heard of anyone in the car business doing compression tests on warm engines because it just isn't done that way. Sorry.
If you take a compression test hot or cold there will not usually be much if any difference. If the bike sat long enough there can be a significant difference as the rings/cylinders can be dry. Not just overnight though. , If you think adjusting valves will make much difference you are mistaken. That is unless they are way, way off. It jut doesn't work that way.
I suspect there will be no real difference between hot and cold but the correct way is warm.

Mike

Worked on the "big rigs" for 45 years now just riding my Wing whenever I can. Gets cold in Wisconsin.
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post #18 of 31 (permalink) Old 01-23-2017, 09:45 AM Thread Starter
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Ya I don't think valve adjust is going to help either, but I'd like to eliminate it. What are rebuild/replace options for these engines? Is it more cost effective to just get a new one?
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post #19 of 31 (permalink) Old 01-23-2017, 10:00 AM
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Billy,
Some history might help. The engine might be just fine. If you have a bike that is 40 years old and has an ever so slight skip, as you can't hardly tell. Is it worth all the time and trouble? Might buy used and get a worse one. It is near impossible to find parts for your 1977. Why are you going through all the trouble. If you just discovered a slightly low compression aren't you just looking for trouble when you could be riding?
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Mike

Worked on the "big rigs" for 45 years now just riding my Wing whenever I can. Gets cold in Wisconsin.
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post #20 of 31 (permalink) Old 01-23-2017, 06:02 PM
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Test with wide open throttle???
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