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Discussion Starter #1
Hi, i repeated a compresion test:
105psi front
95psi rear
Same hot or cold, wide open throttle.
44000km
On previous test at 29000km i had exactely the same numbers.
Almost no oil consumption over any change interval (6000km)
Valve clearance always 0 for closer and 0.10mm opener.
Cam timing not checked yet.
I have to clean tb every 6000km because it became dirty.

It is common? Any advice?

Thanks
 

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Hi, i repeated a compresion test:
105psi front
95psi rear
Same hot or cold, wide open throttle.
44000km
On previous test at 29000km i had exactely the same numbers.
Almost no oil consumption over any change interval (6000km)
Valve clearance always 0 for closer and 0.10mm opener.
Cam timing not checked yet.
I have to clean tb every 6000km because it became dirty.

It is common? Any advice?

Thanks
What model and year is the bike?
 

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Keep in mind without a reading with your gauge at a very early mileage it can be hard to tell. The difference between the two could be considered not ideal but in the useable range. If concerned do 2 things.

Test again with a quality gauge that is not yours to back up the results.

do a leakdown test to measure percentage of loss piston to cylinder as well as valve seal.

I did have a 900ie go through the shop that had burnt valves due to them not being adjusted so this is your main concern and a leakdown will answer the question. You could also simply check that the valves are closing and have clearance on the openers at TDC.

On the gauge a simple Schrader valve of the wrong pressure rating will cause different readings so if another gauge reads different but similar between the different cylinders you can use yours as you have to compare .
 

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Gauges on compression testers are notorious for being inaccurate. That being said, if you have 2 consistently different numbers you can safely assume that rear is 10ish psi lower than the front, but not that your front is actually 105 and rear 95. I don't know the specs for your bike but I would think a 10psi difference between cylinders is within spec, as it is for many vehicles, and keep in mind that no 2 cylinders will have exactly the same compression. Having a very low oil consumption is a good sign and for me could reinforce the notion that your bike is in fine health for its mileage. Common causes for low compression are piston rings and poorly seating or burnt valves, but with a bike that is running within spec and otherwise fine I would not try to chase a problem that might not exist by dissembling your heads. Normal wear on high-mileage engines include piston rings tolerances becoming wider and pitting and deposits on valve seats and valve mating surfaces, both resulting in lowering compression over time.

Another thing you could look at is shining a flashlight down the spark plug hole of both cylinders and seeing if your rear cylinder head looks substantially cleaner than the front. This can indicate that there is a hole in your head gasket and coolant is steam cleaning the cylinder. Past some simple checks like that I would have your engine looked at by a professional if you are adamant about getting to the bottom if the psi differences, and you are not confident about working on engines.
 

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dadouzzu gave us all the clue.
I have to clean tb every 6000km because it became dirty.
No oil use is suggesting good rings. If the throttle body needs cleaning that regularly combustion gasses are coming back into the inlet track. Either massively wrong inlet timing or valves leak.
 

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Discussion Starter #7
Thanks forr all the comment

I know, most compression tester are chinese junk.
There are 3 type of tool on ebay/ amazon
1 cheap cinese crap
2 a bit more expensive european remarked chinese crap (mine)(same object as 1 with eu tag)
3 superexpensiveand unavailable tools. (Like 500euro bgs that is a german brand that also buy from china and apply eu tag)

I know that my flexible adapter has a crappy valve that loose about 1bar.

The universal adapters (with rubber cone at the end) are better.
I check them measuring a good pressure regulator output.
Anyway i will try to do some other check on the tool.
Asap i will also buy a leakage tester (try to not buy crappy china junk :)

@ducvet
All the valve were at 0 closing and 0.1 opening except for horiz intake that has a broken half ring and 0.08mm clearance.
I replaced the half rings on this and the clearance became less than 0.03.
Anyway i don't know how it was prior to 29kkm

@gws and @Stillrollinalong

I will update as soon i can do a leakdown test.
I had disconnected the crankase breathing hose from the breather tank and put it in a white rag to see if the dirt come from crankase.
There is a little smell of burnt oil when i heat up the bike but no smoke or oil residue in the last 100km.

The bike is not liquid cooled and has no leakage outside the engine.
981971


Maybe the intake timing is not perfect but not massevely wrong
 
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