Poor compression.

[Swiss Toni]

‘96 B6

Getting 100psi on this motor. Should be 142. No valve leakage at all. 

Bore nearing limit, but still in spec. 
Pistons are .0012” over limit (undersized).                                              
 

Rings:  Free end gaps out of spec, but fitted gaps in bore around .004” under limit. So, why is compression nearly 1/3 under what it should be?

I might add, the motor has just under 18k on it  

 

Edited May 23, 2023 by Swiss Toni

[Gixer1460]

Combination of everything being nearly f**ked = it's totally f"*ked!

[imago]

I take it you have it in bits now? So it's down on compression but doesn't look like the pressure is escaping, just not enough. In which case something's dropped the cr.  Is it an original head gasket?

[Swiss Toni]

3 hours ago, imago said:

I take it you have it in bits now? So it's down on compression but doesn't look like the pressure is escaping, just not enough. In which case something's dropped the cr.  Is it an original head gasket?

Yup. Brand new OE Suzuki.

[Dezza]

What is the variation among all four cylinders? Did you take the readings when the engine was warm? Has the guage always been reliable? It may be something simple like a low-reading / sticking guage.

[Swiss Toni]

The thought had crossed my mind, Dezza. 1,2 and 3 were just over the 100, 4 was around 90. Any recommendations for a decent quality gauge?

[DAZ]

Genuine 18k should be spot on ,if it's not the guage could it be bore glazing? 

[Dezza]

8 minutes ago, Swiss Toni said:

The thought had crossed my mind, Dezza. 1,2 and 3 were just over the 100, 4 was around 90. Any recommendations for a decent quality gauge?

Maybe borrow another gauge or preferably two. You'd then be able to see any effects of measurement error due to variation in the readings from different gauges. I have a Sealy gauge and it seems fine but next time I do a compression test I'll try and borrow others for comparison

[imago]

If it's that even across the four it might be worth having a look at the cam timing. If the valves are closing late compression won't be a complete stroke. 

[KATANAMANGLER]

Do you have carbs on it yet?

[Swiss Toni]

@imagoCam timing by the book. Lined up correctly.

@KATANAMANGLERNo carbs fitted yet.

[slayer61]

Valves not quite closing or shite on the seats?

[imago]

30 minutes ago, Swiss Toni said:

@imagoCam timing by the book. Lined up correctly.

@KATANAMANGLERNo carbs fitted yet.

With all cyls that far out and fairly even with all the shared stuff sounding as it should be then it's looking like @Dezzais on the money.

[wraith]

Have you tried starting it yet and dose it start ok or a bit of a bugger? 

Just if the comp is that low, it would not be a easy bike to start from cold.

[Swiss Toni]

2 hours ago, wraith said:

Have you tried starting it yet and dose it start ok or a bit of a bugger? 

Just if the comp is that low, it would not be a easy bike to start from cold.

Engine’s out, Sean. 

[Swiss Toni]

@DAZYes, bores glazed. 
@slayer61Valves sealing perfectly. 
@imagoI’ll check valve timing on assembly, but I’m sure it was ok. 

[fab]

check your compression gauge on a good engine you have, at least you will know if its working ok

[Pegleg]

A healthy battery helps. Sluggish battery can prevent compression building. 

[Pegleg]

Also trying putting oil down the plug holes before testing. If it comes up Its ring wear. 

[Gsxrsam]

Buy a leakdown tester.

if you have a compressor they are much better at the job......