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Author Topic: Compression tests on cylinders  (Read 4035 times)

Offline jamestnewsonr65

  • Lives in Foothills of Mt. Olympus
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  • Posts: 232
Compression tests on cylinders
« on: April 24, 2017, 09:21:23 AM »
So after a few problems starting my bike (Recent posts) it turned out to be a combination of spark plugs, battery power and needing a general tune up.

The timing was slightly off, but all is working well now and the bike fires up nicely.

I did a compression test to see if this was part of the overall problem and I got results of 55psi on the left and 80psi on the right.

Should I be looking to check the piston rings and tube seals?

I checked this by removing the 3 pin lead under the front cover, removing the spark plugs and then fitting a compression tester to each cylinder whilst cranking the bike for 2/3 times.

From memory the PSI should be over 120psi at least, so this is a little concerning.

Any advice appreciated.

1983 R65LS completely refurbished to my liking.
1985 R80 nearly stock rebuild (basically new bike).
1981 R65 (box of bits).

Offline wilcom

  • Mt. Olympus Resident
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  • Posts: 1499
Re: Compression tests on cylinders
« Reply #1 on: April 24, 2017, 09:49:17 AM »
Did you hold the throttle wide open?
Joe Wilkerson
Telephone man with a splash of Data
Menifee, CA

Present:
1984 BMW R65LS "Herr Head"
past:
1982 BMW R65LS
1979 R65
1980 R65
1982 R80RT
1974 R90/6
1972 R75
1964 R50/2
19xx R27
ZX-11

Offline Bob_Roller

  • Global Moderator
  • Mt. Olympus Resident
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  • Posts: 9120
  • -7 hours GMT
Re: Compression tests on cylinders
« Reply #2 on: April 24, 2017, 03:37:16 PM »
You need to get at least 10 compression cycles to get a proper compression test .

You can stop when the pressure on the gauge doesn't go any higher .

As wilcom has said the throttle needs to be held full open during the test .
'81 R65
'82 R65 LS
'84 R65 LS
'87 Moto Guzzi V65 Lario
'02 R1150R
Riding all year long since 1993 .
I'll give up my R65, when they pry my cold dead hands from the handlebars !!!!!

Offline Tony Smith

  • Mt. Olympus Resident
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  • Posts: 2331
  • Graduate, Wallace and Gromit School of Engineering
Re: Compression tests on cylinders
« Reply #3 on: April 24, 2017, 03:47:08 PM »
Quote
The timing was slightly off, but all is working well now and the bike fires up nicely.

I did a compression test to see if this was part of the overall problem and I got results of 55psi on the left and 80psi on the right.


I checked this by removing the 3 pin lead under the front cover, removing the spark plugs and then fitting a compression tester to each cylinder whilst cranking the bike for 2/3 times.

From memory the PSI should be over 120psi at least, so this is a little concerning.



Firstly I'd be buying a new compression tester. Whilst an R65 engine might run with 50~60 psi compression, you would need ether to get it started.

Whilst I applaud the thought that went into disconnecting the beancan, that didn't really stop the coils from being charged up - next time simply disconnect the positive lead to the coil - which as an added bonus, does not require the removal of the front cover :-)

In respect to checking over rings etc, my question is "how well known is this bike to you?". If it is an unknown that you have just restored to life then I would have checked valve guide clearance, had a look at valve sealing and, give the relatively low cost, probably thrown new rings (and if an iron bore a de-glazing hone) at it because then I could restart the "counter" to when I next needed to look.

On the other hand, if the bike is known to you and the distance  since last top end refresh is around 50,000km (30,000m) then I'd do the top end refresh irregardless of inspected condition. OR, if it is more than 5 or 6 years since the heads were last off irregardless of mileage.

It may be because the wife's original R65 engine was destroyed by dropping a valve (at 60,000km and 9 years since new) or that my own R65 came to me as a result of dropping a valve (at 52,000km and 10 years) but if I take the heads off an airhead these days I replace at least the exhaust valves - they are cheap compared to new head/piston/cylinder and although I have no "proof" I reckon combustion tempos are a bit higher on unleaded fuel.
1978 R100RS| 1981 R100RS (JPS) | 1984 R65 | 1992 KLE500 | 2002 R1150GSA |

Offline jamestnewsonr65

  • Lives in Foothills of Mt. Olympus
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  • Posts: 232
Re: Compression tests on cylinders
« Reply #4 on: April 24, 2017, 05:00:26 PM »
Not sure I had the throttle wide open to be honest. I'll try it again and make sure I do.

I've had the bike for 3 years and restored it apart from the engine. It had been regularly serviced and I have every receipt since new. Covered 18000miles and runs fine. No smoke, oil or anything burning/ leaking.

1983 R65LS completely refurbished to my liking.
1985 R80 nearly stock rebuild (basically new bike).
1981 R65 (box of bits).

Offline jamestnewsonr65

  • Lives in Foothills of Mt. Olympus
  • **
  • Posts: 232
Re: Compression tests on cylinders
« Reply #5 on: April 24, 2017, 05:03:01 PM »
Here's a pic for the hell of it.
1983 R65LS completely refurbished to my liking.
1985 R80 nearly stock rebuild (basically new bike).
1981 R65 (box of bits).

Offline Bob_Roller

  • Global Moderator
  • Mt. Olympus Resident
  • *****
  • Posts: 9120
  • -7 hours GMT
Re: Compression tests on cylinders
« Reply #6 on: April 24, 2017, 09:09:27 PM »
Unleaded fuel has been mandated here in the US for a bit over 44 years, I have not seen any valve related issues in this time on vehicles here .
'81 R65
'82 R65 LS
'84 R65 LS
'87 Moto Guzzi V65 Lario
'02 R1150R
Riding all year long since 1993 .
I'll give up my R65, when they pry my cold dead hands from the handlebars !!!!!

Offline Tony Smith

  • Mt. Olympus Resident
  • ****
  • Posts: 2331
  • Graduate, Wallace and Gromit School of Engineering
Re: Compression tests on cylinders
« Reply #7 on: April 24, 2017, 10:42:05 PM »
Quote
Unleaded fuel has been mandated here in the US for a bit over 44 years, I have not seen any valve related issues in this time on vehicles here .

Bob - 44 years? Which parallel dimension is yours in?
1978 R100RS| 1981 R100RS (JPS) | 1984 R65 | 1992 KLE500 | 2002 R1150GSA |

Offline Tony Smith

  • Mt. Olympus Resident
  • ****
  • Posts: 2331
  • Graduate, Wallace and Gromit School of Engineering
Re: Compression tests on cylinders
« Reply #8 on: April 24, 2017, 11:24:38 PM »
Quote
Unleaded fuel has been mandated here in the US for a bit over 44 years, I have not seen any valve related issues in this time on vehicles here .

Bob - that may be the case in your dimension, but in mine I think you will find that mandatory unleaded fuel didn't commence until the 80/90s.
1978 R100RS| 1981 R100RS (JPS) | 1984 R65 | 1992 KLE500 | 2002 R1150GSA |

Offline Tony Smith

  • Mt. Olympus Resident
  • ****
  • Posts: 2331
  • Graduate, Wallace and Gromit School of Engineering
Re: Compression tests on cylinders
« Reply #9 on: April 24, 2017, 11:26:03 PM »
Quote
Quote
Unleaded fuel has been mandated here in the US for a bit over 44 years, I have not seen any valve related issues in this time on vehicles here .

Bob - 44 years? Which parallel dimension is yours in?


bod, sorry for the multiple messages - the forum is going crazy here and i thought my original post went directly to cyber cemetery.
1978 R100RS| 1981 R100RS (JPS) | 1984 R65 | 1992 KLE500 | 2002 R1150GSA |