2007 AE Has a low piston 4 pressure

Jman · Oct 18, 2024

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 · Oct 18, 2024

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 · Oct 18, 2024

Whooshka said:
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 · Oct 19, 2024

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 · Nov 1, 2024

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 · Nov 1, 2024

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 · Nov 1, 2024

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 · Nov 1, 2024

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 · Nov 1, 2024

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

Jman · Nov 1, 2024

The time-serts are a metal sleeve. They also sell a high temp thread lock compound. It should be pretty good.
Not cheap but its a good tool to have.

Panman · Nov 1, 2024

Sure you can't do it with the head on? Pulling the head requires new head bolts as I recall. 50 years or so we did a few Triumphs with the HeliCoils and what chips fell into the combustion chamber just burnt off.

torch · Nov 2, 2024

Whooshka said:
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?

The casting around the plug is deeply recessed and small diameter. I don't know that you could find a plug with a larger thread with a hex small enough to fit a socket around it and the correct specifications (heat range, lengths, etc.) of the plug itself.

Plus it would be a PITA to be changing plugs with 3 of one kind and 1 of another.

Whooshka · Nov 2, 2024

Good point.

Jman · Nov 2, 2024

Panman said:
Sure you can't do it with the head on? Pulling the head requires new head bolts as I recall. 50 years or so we did a few Triumphs with the HeliCoils and what chips fell into the combustion chamber just burnt off.

I probably could but it would be nearly impossible to see what I am doing. I also want to have a look at the cylinder. I did manage to get pressure after putting some oil down there which could mean a bad piston ring. The engine was still warm.

Jman · Nov 4, 2024

Upon further inspection.
I can't find a single thing that is not wrong with piston 4.
3 out of 4 valves are out of spec on the long side by .02mm+
The exhaust is not air tight.
The spark plug threads are trashed.

I think that there was a low speed lay down on the left side of the bike which wrecked the right hand side.
Or perhaps someone did not tighten the bolts on the piston head in the right order.
The engine is part of the frame on this bike.
When the bike runs pretty bad at low speeds and you don't have a clutch to work with I can understand how the bike could be put down at low speed.

Pretty sure I can fix the problems but its annoying.
I think someone tried to fix the problem but made it worse.

Might do an Ivan flash on the ECU if I can't get it to run better at low speed.

2007 AE Has a low piston 4 pressure

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