Weird compression test results!

[Tetronator]

Well then, back again with something weird on my Shadow...


It's time for the bikes 10K km maintenace, so valves, oil, ect. So I pull the bike apart check the valve's and front cylinder seems fine and only the rear cylinder exhaust valve needed a little bit of adjustment but was fine nonetheless.
So I replace the filter and oil (pouring oil trough the valve cover is way easier ) and went on to do a compression check, mind you cold engine and no pesky CV carbs to block the intake.

This is what came out:

Compression test results, Cold engine, no carbs
Preferred Values : 12.26 till 14.22 bar / 178 till 206 psi

Rear cylinder in bar (psi) :
(Dry) No Oil: 7.5 (105) 7.7 (110) 8.0 (115)
(Wet) Oil: 12.5 (180) 13.0 (190) 12.5 (185)

Front cylinder in bar (psi) :
First try:
(Dry) No Oil: 6.0 (85) 2.0 (30) 2.0 (30)
(Wet) Oil: 4.5 (65) 4.8 (70) 5.5 (80)

Second try (No extra oil):
11.3 (165) 7.8 (120) 7.2 (105) 7.8 (110)

Third try (Added extra oil):
11.4 (165) 10.5 (150) 9.9 (140) 9.2 (135)

So anyone here that can make heads or tails out of this?

I'm thinking worn out piston rings... All tough they have been recently replaced along with a reasonably new second hand engine.
It's been using some oil over the last 10k KM nothing to worry about but here's how to spark plugs look.
Upper ones are from the front cylinder, yes, two per cylinder .



Other than one valve rattling it's been running like a champ, no smoke or nothing. Just weird compression test results...

[Tetronator]

No-one has a clue on whats causing this? Reassembly of the bike takes a while so I'd rather deal with it now than having to disassemble/assemble it again.
Them carbs are annoying, I want a dieselbike... First comes moving to a new house I guess.... So I have space to build it...

[coachgeo]

If it runs fine....... then run it. IMHO sounds like you'll find that your just chasing the right procedure to eventually get balanced readings. Button it back up. Ride it. Get bigger house or co-rent a garage with some auto or bike enthusiast and start your diesel build!

If Im wrong the issues will make the bike run like crap about the time your ready to start your diesel build so nothing lost.

[Tetronator]

Well I still have to test it with a warm engine, but that means reassembling everything and the stock airducting on these things SUCK. So if I have to reassemble everything just to pull it apart again, that'd be annoying.

And I'd like to be able to ride this bike as I'm building my dieselbike, I still need transport.
After the dieselbike is done the dieselbike will replace this bike as a workhorse and it's going to get chopped, it has served me well and I will keep it as a weekend playing, its still my first motorcycle afterall.

I'd still like to find out what's causing these results...

[coachgeo]

....And I'd like to be able to ride this bike as I'm building my dieselbike, I still need transport.s...

ahhhh... then it definitely makes since to dig deeper into the situation. Wish I could add some .02 to help

[Tetronator]

That's OK, effort is appreciated.

[albertaphil]

So is the weirdness you're talking about the low compression on the front cylinder; dry and wet, followed by almost acceptable numbers on further tests?

I would guess a sticking piston ring due to overheating, hence the abrupt change. The plugs from the front cylinder look like they have been running leaner than the ones from the rears. Leaner=hotter leading to possible overheating of the front cylinder? But the rings seem to have unstuck themselves.

Beyond that I tend to agree with coach...get yourself an infrared thermometer, put 'er back together and richen the front carb and checking the exhaust temperature to verify, and ride.

Sorry for all the petrol talk. You're reminding me why I like diesel...

[Tetronator]

First of all, you have nothing to apologize for, I opened this tread about MY petrol bike.

Hmm, didn't think that it might be an overheating issue... I advanced the timing off my engine by 4 degrees, but then i'd would've run lean on the rear cylinder as well... It can run stock on 70-octane rating gasoline, standard in Netherlands is 95/97. Gives me a bit more MPG and torque.
Unless the damned stock air ducting is leaking in false air again, it has a tendency to do that... Main suspect is the airducting for me now. That same airducting makes it VERY hard to remove the carbs and adjust the settings on them. I've been wanting to replace them with intake funnels since forever now.

https://www.youtube.com/watch?v=EDpm3an ... MPVSIn5naQ

I'll see what I can do about that IR thermometer, put it back together, warm it up and properly check the compression again.

Yeah, running a false air breathing carb trough the Alps for 7000km might've caused this I guess... I didn't exactly go easy on the little Honda.



Totally worth it tough...

[Tetronator]

Well then, I managed to fix it... Somehow!

Current compression readings:
Warm engine, carbs in place.
Preferred Values : 12.26 till 14.22 bar / 178 till 206 psi

Front cylinder in bar (psi) :
(Dry) No Oil: 10.2 (145) 10.2 (145) 10.2 (145)
(Wet) Oil: 12.8 (185) 12.2 (180) 12 (175)

Rear cylinder in bar (psi) :
(Dry) No Oil: 10.5 (150) 10.5 (150) 10.5 (150)
(Wet) Oil: 11.9 (170) 11.2 (165) [Drained battery]

This all just by warming up the engine! All tough, I think the first run with oil might have dislodged a stuck piston ring in the front cylinder.
Continuing investigation revealed that my carburators were totally out of sync. Yet it ran, Honda ftw. Added to this was that my
airduct spagetti probably had a leak at the carb mount and airbox mount. So after syncing the carbs, it ran like a champ! I will still try to get
a hold off one of those fancy IR thermometers and a different compression tester, to be sure.

Airduct Spagetti.


I thank you all for your imput and patience for a sparkplug driven machine.

Which is equally at home running oil it seems. (Note this before Carb syncing.)
https://www.youtube.com/watch?v=uXMxqlsuWSQ