2007 AE Has a low piston 4 pressure

[Jman]

Well I went and bought myself an FJR
It only had 14k miles and the price was low. It is a clean looking bike.
When riding it there is a bit of bogging at low speed and a little vibration in the handle bars at speed.
I really just thought it needed a throttle sync, and clutch engagement adjustment.
When I tested the piston pressure I got 200+ psi in pistons 1-3.
Piston 4 was around 140 psi. Threw some oil in the piston and I got 200+ psi.

Looks likes I (hopefully) need a piston ring.
Has anybody else had this problem in a low mileage FJR?
I have some experience working on engines and the service manual but any advice would be appreciated.
Thigs / quirks particular to this engine for example.

 

[Whooshka]

One easy fairly cheap thing to try is pick up a bottle of Yamaha Ring Free. You might have a ring that's "stuck" and not sealing against the cylinder wall correctly. This might help.

https://www.amazon.com/CYCLEMAX-Yam...7743&sprefix=yamaha+ring+free,aps,107&sr=8-16

 

[RossKean]

One easy fairly cheap thing to try is pick up a bottle of Yamaha Ring Free. You might have a ring that's "stuck" and not sealing against the cylinder wall correctly. This might help.

Agree! Certainly can't hurt.

 

[Diablo1]

Ring free is a very good suggestion, along with an Italian tuneup - put some miles on it at speed. That bike has been sitting around in storage and hasn’t been ridden much. Issues to check for are ignition switch and ground spiders.

 

[Jman]

Upon further investigation I found that the spark plug threads are ruined.

My testing tool got stuck and when I ran a thread chaser down there it had quite a bit of wobble even when bottomed out. Some gorilla screwed a spark plug in there sideways. That stripped out metal went into my piston...

So it looks like I am going to have to remove the piston head and use a time-sert tap on it.
While I am at it I am going to replace the piston ring.
Going to replace the cam chain tensioner with a green dot one.
Then I have to make sure the timing is good, check valves.
Exhaust is not sealing properly so I have to put new gaskets on there.

This is why I buy bikes in the fall/winter months. I do enjoy this kind of stuff but I wish the bike just needed a tune up.

Have to get time-sert kit, gaskets, cylinder head bolts and lots of little doodads.
Pretty absurd what this stuff costs. Almost the cost of buying a used engine.
All because someone was careless with a spark plug.

Always hand tighten bolts at first and use a socket that firmly fits your spark plug.

Anyhow Ill keep you all informed on my progress.

 

[torch]

I've had limited success with spark plug thread inserts into aluminium heads. They work initially but have a tendency to come out with the plug eventually. I'd seriously consider looking for a good used casting.

 

[RossKean]

If you decide to go for a replacement engine rather than fixing yours (some great deals pop up on eBay), remember that the "AE" is different from the "A".
It is, however, reasonably easy to convert. With your AE donor, it wouldn't even cost parts.
https://www.fjrforum.com/threads/converting-gen-2-ae-to-a-engine-is-it-possible.161693/
Some photos missing but enough information is there.

 

[Whooshka]

Just throwing this out there, more of a question than a suggestion... would drilling and tapping a hole for a larger threaded diameter (not longer) plug work?

 

[Rocnsanman]

Back IN The Day, all we had were HeliCoils to repair our VW stripped out spark plug holes. Now those were a PITA. Time Serts came along and were a major step in the right direction. With patience and a skilled hand, a repair with a Time Sert will last a lifetime.
Good luck