R1 Low power, cylinder pressure

imadraver

Make Every Moment Matter!
Control Rider
My b-bike 04 R1 had a water oil pump failure last year and overheated pretty bad. Fixed that but since then it has very low power problem I'm trying to diagnose.

I went to test the cylinder pressure and see if a valve or head gasket may be out of whack. Started with #4 good, #3 good, #2 and#1 bad like no compression...nothing! Recheck #4, bad like nothing, wait what?! Why would #4 retest fail?

Maybe the air cutoff valve is messing with my cylinder pressure tests?

Ideas?

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bmart

Control Rider
The only time I've seen readings change is when the seal isn't good or the Schrader valve in the compression tool isn't good.
 

tdelegram

Control Rider
Could there have been excess oil in the cylinder first test? One way to diagnose rings is to add oil through the spark plug hole and if compression materially increases your rings are bad, if it's valves there won't be any change in the reading.
 

chrisplm

Chris
Control Rider
I had a similar thing happen where my compression tests were reading all over the place... It turned out the adapter for the compression tester wasn't seating right in the spark plug holes. Sometimes it seated enough to get some compression, sometimes not.
The part of the adapter above the threads was too big around to fit properly. I ended up taking some material off the adapter, then all was good. This doesn't help explain why you are seeing power loss, but may help you get some consistent pressure numbers.
(Also, make sure your throttle body valves are all forced open so the cylinder can draw air in freely)
 

imadraver

Make Every Moment Matter!
Control Rider
My b-bike 04 R1 had a water oil pump failure last year and overheated pretty bad. Fixed that but since then it has very low power problem I'm trying to diagnose.

I went to test the cylinder pressure and see if a valve or head gasket may be out of whack. Started with #4 good, #3 good, #2 and#1 bad like no compression...nothing! Recheck #4, bad like nothing, wait what?! Why would #4 retest fail?

Maybe the air cutoff valve is messing with my cylinder pressure tests?

Ideas?

Sent from my SM-A716U using Tapatalk
Appreciate the tips so far. I decided to go with the service manual approach which says to measure the valve clearance first, then check the cylinder pressure. My hope is maybe I'll see something else that's out of whack. Already I'm noticing the air cut off reed valves have a lot of carbon buildup. Maybe that's creating a situation where the pressure test is not accurate because those would be shut off in normal running condition.

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Yurzi

Control Rider
Appreciate the tips so far. I decided to go with the service manual approach which says to measure the valve clearance first, then check the cylinder pressure. My hope is maybe I'll see something else that's out of whack. Already I'm noticing the air cut off reed valves have a lot of carbon buildup. Maybe that's creating a situation where the pressure test is not accurate because those would be shut off in normal running condition.

Sent from my SM-A716U using Tapatalk

The air cut off valve has nothing to do with cylinder psi. It just adds air to the exhaust in order to help burn up gasses for emissions. Its normal to see carbon build up there. The entire system is often removed, and block off plates added to the valve cover. It is not necessary for the engine to run.

Verify that the gauge isn't faulty. Never hurts to check valve clearance. If the gauge is good then you most likely have a problem with a valve seating/closing.
 

imadraver

Make Every Moment Matter!
Control Rider
Well they always say trust your gauges but apparently my comp tester just went bad after that 2nd cylinder test! I checked all valve clearances and hours of inspecting cleaning, I see nothing and decided to rent AutoZone comp tester, all comp was fine!!! At this point I'm back to basic things like spark plugs and throttle bodies.

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bmart

Control Rider
You don't want to get into Segal's law, but having a backup tool can be helpful. For me, the compression tester is used so rarely that I frequently have to put a new Schrader valve in the end when I use it.

This is the same with the myriad of PSI gauges at the track. If you try 10 on your tire, you'll get varying answers! I had my set/calibrated at a guage shop, so I'm comfortable that everyone else's are wrong. lol
 
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