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K100-forum.com » Technical, repair and troubleshooting » Engine and transmission » Low compression on K75

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1Back to top Go down   Low compression on K75 Empty Low compression on K75 Sat Mar 12, 2022 12:32 pm

Nom721

Nom721
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I’m getting towards the end of a major restoration of my K75 and was starting up for the frist time in a very long time. I was a bit ancious to push the starter button but after a couple of revs it started to fire, erratic but it ran Laughing
I turned it off and decided to do a compression test. Cyl 1 and 3 both did about 10 bars but no 2 only did 4-5 bars. I guess that’s the reason for the bad running. The question is now what is the most likely reason for the lack of compression? Where would I look  first?

    

2Back to top Go down   Low compression on K75 Empty Re: Low compression on K75 Sat Mar 12, 2022 12:52 pm

robmack

robmack
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Check valve clearances to begin with.

Can you do a leak down test, which might be more telling than a compression test?


__________________________________________________
Robert
1987 K75 @k75retro.blogspot.ca
http://k75retro.blogspot.ca/
    

3Back to top Go down   Low compression on K75 Empty Re: Low compression on K75 Sat Mar 12, 2022 12:59 pm

Nom721

Nom721
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I will have a look at the valve clearance. How do you do a leak down test?

    

4Back to top Go down   Low compression on K75 Empty Re: Low compression on K75 Sat Mar 12, 2022 1:08 pm

Nom721

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Just found an article about leak down test. Try that as well.

    

5Back to top Go down   Low compression on K75 Empty Re: Low compression on K75 Sat Mar 12, 2022 2:16 pm

moriarti

moriarti
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Inject some light oil into No 2 then compression test again if its now good as others Suspect sticking piston rings which will free off with running HOPFULY Very Happy Very Happy
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__________________________________________________
1984 k100 rs red/black VIN  0004449 Now sold to Olaf
    

6Back to top Go down   Low compression on K75 Empty Re: Low compression on K75 Sat Mar 12, 2022 8:37 pm

92KK 84WW Olaf

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Sticky piston rings are very high on the suspect list after a long lay down.

Valve clearances are so very easy to check. If you are doing it be very careful retorquing the cam cover bolts, the torque setting is extremely low.


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011157 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 58,200 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 51,800 miles.
1983 K100RS 0004449 Odette R100 colours 58,000 miles. Sprint fairing now 63,390 miles

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

7Back to top Go down   Low compression on K75 Empty Re: Low compression on K75 Sun Mar 13, 2022 9:02 am

Dai

Dai
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And replace the rubber bungs under the cam cover bolts. If you don't, you'll end up with a multiple Texas gusher.


__________________________________________________
1983 K100 naked upgraded to K100LT spec after spending time as an RS and an RT
1987 K100RT
Others...
1978 Moto Guzzi 850-T3, 1979 Moto Guzzi 850-T3 California,1993 Moto Guzzi 1100ie California
2020 Royal Enfield Bullet 500
    

8Back to top Go down   Low compression on K75 Empty Re: Low compression on K75 Tue Mar 15, 2022 11:23 am

Nom721

Nom721
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Just did the oil in cylinder trick which restored the compression Laughing It still runs shitty, will do ignition timing, balance throttles. Hope that will do the trick..

    

9Back to top Go down   Low compression on K75 Empty Re: Low compression on K75 Tue Mar 15, 2022 12:05 pm

moriarti

moriarti
Life time member
Life time member
Good news on the (oil trick) now treat the K to a set of BOSH spark plugs. No WORRIES. Razz Razz


__________________________________________________
1984 k100 rs red/black VIN  0004449 Now sold to Olaf
    

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