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Checked my compression today. 165 psi Front and 168 psi Rear. The service manual seems to indicate 206 to 213 psi. Does anyone know if this indicates an issue?
 

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Checked my compression today. 165 psi Front and 168 psi Rear. The service manual seems to indicate 206 to 213 psi. Does anyone know if this indicates an issue?
There is a valve stuck open or not fully closing, or it's time for a re-ring, IMO. Of course make sure you held the throttle open fully that will affect reading. You are at that 20% threshold that I would be double checking my readings if same, I would be first looking at valve clearances and seating. Then if all of that was good, I would put new rings on piston. How many miles on this motor? Oil changed every 4-6k? Using good oil?
 

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The Stryker has 18000 km on it and runs pretty much perfectly. Nothing has been touched on it to date.
 

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Thinking maybe the reading is off. Both cylinders are so close to one another and that usually doesn't happen when you lose compression.
Not sure how you test compression on the bike(not a mechanic) but thinking you maybe have to test each at TDC or something and maybe do a leak down test etc.
If running fine and you don't feel a loss of power, I'd say things are probably fine...
 

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Yes I would say that compression is likely fine given how close the readings are between cylinders. Compression is normally done with the engine warm and the throttle held in the full open position. I should have done a wet test as well and maybe will soon. If you add a teaspoon of oil and then check compression again it will help you determine if its rings are a valve issue. If it goes up its likely you may have a ring issue. Just odd that the technical manual lists a number that is so high. Normally 175 psi is pretty good for an engine.
Leakdown testing is different and you measure what pressure the cylinder will hold at TDC while appying a know pressure. Done this on aircraft engines but not sure its used much on bikes.
 

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I have to disagree with you both (while I am no certified mechanic), the manual gives maximum and minimum pressures readings for a reason. 170.7psi is lowest reading, while 213.3 psi is highest while this is at sea level, anything above 3000ft would change those readings slightly, but either way your readings if correctly achieved are low and indicates wear of some sort. If you are using a good quality compression tester (not harbor freight) I would redo the test making sure i had a good seal at the motor and throttle wide open. If same reading as you stated add teaspoon of oil retest. higher? rings, lower or same check what I said before. You sound knowledgeable , do ignore out of range readings you will only end up with bigger problems. new rings is cheap, bore/piston rings, head work is not.


18km is about 12k miles so shouldn't have that kind of wear. Your making me want to go test mine !
 

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Will redo when I get a chance and repost my findings. Would be nice to see what yours actually is

As soon as I get home from work tomorrow I will do a test on both cylinders just for comparison. I plan to ride to work tomorrow too so it will be all warmed up!
 

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Ok, with normal operating temp , front cylinder is at 197psi- rear cylinder is at 194psi. Sorry didn't get home from work until midnight.

I have 17,000 miles and use Rotella 6 synthetic oil and K&N filter change oil every 5-7k.
 

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Ok, with normal operating temp , front cylinder is at 197psi- rear cylinder is at 194psi. Sorry didn't get home from work until midnight.

I have 17,000 miles and use Rotella 6 synthetic oil and K&N filter change oil every 5-7k.
Just me but I'd change the oil more often. I get that it is synthetic but 4K is the factory recommendation. Since so affordable, I do my T6 changes at 3500...
 

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Just curious what made you do the test initially?
+1 Things like this aren't usually PM even for those that really take their PM seriously.

I'm overdue on checking the valves but I will probably sub that job out. Need to call and get some quotes.
 

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Ok, with normal operating temp , front cylinder is at 197psi- rear cylinder is at 194psi. Sorry didn't get home from work until midnight.

I have 17,000 miles and use Rotella 6 synthetic oil and K&N filter change oil every 5-7k.
I am glad this coversation came up, just checked mine at 100000km and it reads, front cyl. 150 psi rear 147 psi, dry test and does not use oil change oil regular every 10000 ks and it doesn't get hammered, bike now 3 years old and doesn't have any problems, valves were checked at the same time.
 
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