1982 GS550E Compression values in Bar?

[Buddyboy]

Hello everyone, I have just started to restore a 1982 GS550e and I am having a problem, I am trying to find the compression values in Bar for the bike. I was told by the previous owner that the bike had a blown head gasket but im not sure. The haynes manual does not list what the compression reading should be!!!! I have a tester that reads in bar. Does anyone know what the actual value is on an engine that is in perfect runner order?????

I hope this makes sense.

Thanks

Paul.

[SPARKSS]

Hello everyone, I have just started to restore a 1982 GS550e and I am having a problem, I am trying to find the compression values in Bar for the bike. I was told by the previous owner that the bike had a blown head gasket but im not sure. The haynes manual does not list what the compression reading should be!!!! I have a tester that reads in bar. Does anyone know what the actual value is on an engine that is in perfect runner order?????

I hope this makes sense.

Thanks

Paul.

Howdy Paul. Each bar of pressure equates to 1 atmosphere = 14.7 psig = 101.3 kPa for conversion (this is close enough). Typical gasoline engines have a compression ratio between 8:1 (low) to 12:1 (high) so you can figure that compression at cranking speed (good ability to fill cylinders) will be roughly will yield 90 - 180 psig with the typical values being 90 - 120 psig or
6 to 8 bar. Of course all this being typical near sea level so if you're at 7500 ft you'll have to see what typical atmospheric pressure is there and adjust downwards accordingly. Likewise.....I hope this makes sense!

[Buddyboy]

1982 GS550E Best Compression Test Method???

Thanks for your reply, very helpful, could some one please explain the best way to test the compression? At the moment I am removing all the spark plugs and screwing the guage in one of the plug threads and attempt to start the bike on the button etc. Doing it this way I seem to get very inconsistant values. I understand that they should be between 6 and 8 bar? Im fairly new to working on bikes and im struggling a bit!!!!

Thanks

Paul.

[Nessism]

I don't know about the 16 valve 550's but the proper pressure for the 8 valve'rs is 9.0 - 13.0 kg/cm^2 (128-185 psi)

[hikermikem]

Compression values for 16 valve, 4 cyl 550 should be:

10-14 kg/cm2, (142-199 psi)
Low Limit = 8 kg/cm2 (114psi)
max difference between cly = 2 kg/cm2 (28psi)

valve clearances are:

.08-.13mm (.003-.005"), both intake & exhaust sides when STONE COLD

This data is from my 1983 factory manual

[SPARKSS]

Thanks for your reply, very helpful, could some one please explain the best way to test the compression? At the moment I am removing all the spark plugs and screwing the guage in one of the plug threads and attempt to start the bike on the button etc. Doing it this way I seem to get very inconsistant values. I understand that they should be between 6 and 8 bar? Im fairly new to working on bikes and im struggling a bit!!!!

Thanks

Paul.

Howdy Paul......You're basically running a cranking compression test ok. I'd suggest that you connect a low rate battery charger across the battery while doing this just to keep cranking speed up (more consistent results). What you want to do is to crank for an equal repetition of compression "pulses".....i.e. crank for 5 or 6 pulses (you'll hear this as compression builds under your gauge). What you're looking for is: Good compression rise (should peak in 3 to 5 pulses).....Good compression (6-8 bar at least....you should know what to expect by the specs of your engine)........Good consistency across cylinders (1 at 4 bar and the rest at 8 would indicate a bad problem.......2 adjacent cylinders very low might indicate cross communication - blown head gasket etc on some engines etc). Get the picture? IF you see low compression, try adding a squirt or 2 of engine oil into the cylinder and see if it rises.....may indicate worn rings. Keep in mind that you can find low compression and the problem may be due to a leaking valve(s).

Also note.......repeat your tests at least twice (2 or 3 times) each to confirm your results.

[Steve]

One other thing not yet mentioned in this thread...while you are cranking, HOLD THE THROTTLE OPEN. :shock:

You are trying to compress air, so let it get as much as it can. 8-[


.

[beby99]

Another thing not mentioned (unless I missed it) engine should be fully warmed.

[SPARKSS]

One other thing not yet mentioned in this thread...while you are cranking, HOLD THE THROTTLE OPEN. :shock:

You are trying to compress air, so let it get as much as it can. 8-[


.

Kind of a moot point there.......The engine should easily run on the VERY small amount of air available to it at closed throttle. The key points are that there's minimum compression available to start and then sufficient compression to provide acceptable performance and last but not least, across all cylinders.

[SPARKSS]

Another thing not mentioned (unless I missed it) engine should be fully warmed.

Another moot point here. Although you may be comparing your compression results to a service manual (which requres a warmed engine), use of compression testing may be to diagnose why an engine won't start in the first place. I've seen quite a few times over the years, where an engine with no mechanical problem had low compression (and even a couple of times almost NO compression!) in one or more cylinders due to being washed down with gasoline due to other problems, causing a no start condition. In this sort of case, ompression testing is used in addition to other diagnostic routines to confirm what you're dealing with. Just a little food to help you think outside the box