New FJ1100...low compression, no intake valve clearance

[SlowOldGuy]

Just curious, knowing that the intake valves were not correct, why didn't you fix that then re-test?

Be sure to replace the rubber seals on the oil galleys and dress up the copper head washers with some sandpaper so they re-seal.  You'll also need a new cam chain tensioner gasket, and of course a new head gasket. 

Check the valves for pitting on the seat face.  You can lap them, but you can NOT grind the valves, they are surface hardened and you'll grind right through the tough zone.  I had bad pitting on my '85 and replaced the set with SS valves.

It's probably a good time to replace the valve cover gasket and the rubber seals on the cam cover bolts.  See RPM Randy for parts.

DavidR.

[andyb]

At 20k (and comfortably over 100 dragstrip passes) when I tore mine apart, the crosshatch was pretty clear and the cylinders looked quite good.  Can't say I'm surprised if they still look good at 50k.  Guessing that the problem's the valves not sealing, fix that and do valve seals while you're there, degree the cams in, and I'd bet you'll find the problem pretty well licked.

[TheRadBaron]

That's the plan.  Hopefully it all works out. 
I mainly decided to pull the head just to put to rest any fears I had of the engine's condition and do some maintenance on the head.  Now I know that the pistons and bores at least appear to be in top shape and I can go through the head and freshen it up.  This could be easier than I thought.  Then again, it might not be...

[racerrad8]

See RPM Randy for parts.

DavidR.

Thanks David.

TheRadBaron,
        For your information I sell an upgraded valve stem seal that will out live the stock seal indefinitely. I also have any and all of the other parts needed to do any head work you need.

Randy - RPM
rpm@swaybar.com

[TheRadBaron]

Thanks Randy, the check's in the mail.  I haven't started the cylinder head disassembly yet, but I think I found the cause of the "suddenly started running poorly" problem.
I started to go through the carbs and I found that the #1 carb had a corroded jet needle and it was stuck firmly in the needle jet.  I had to pop the slide out of the carb body with a screwdriver.  The slide was all the way down, so the #1 cylinder would never have gotten much more "throttle" than idle.  That would explain why my buddy said that it felt like it was running on 3 cylinders. 
I wonder if it's a coincidence that the #1 cylinder was the one that appeared to be passing some oil into the exhaust.  Could the closed carb have done something weird to the vacuum in the cylinder while the rest of the motor was at high load/high RPM that could cause it to suck oil?  So I guess that I'll be needing a new needle and needle jet.  Is there a source for these parts that's cheaper than Yamaha?  Sudco, maybe? 
One more carb question...I know that on the old singles and twins I'm used to, the needle and needle jet can get beat up over the years due to the engine vibration.  The damage is not readily visible, but it effects running.  Would it be advisable to change the needle and jet in all 4 of my carbs?  I know that a 4-cylinder vibrates a lot less than a twin, so maybe it's not too much of a concern.  I'd rather not spend the money if I didn't need to.

[racerrad8]

The needle and emulsion tubes are a high wear item. I have all of the carbs parts in stock and cheaper than all of the rest. But with the parts you are talking about plus the other wear items, it will probably be cheaper and easier to start of with a brand new set which I can supply as well for $400.00

I will not be back to the shop until Thursday, so if you get them torn down completely and inspected, make a list and I can shoot you the prices and you can make your determination.

Randy - RPM

[Kopfjaeger]

be interesting to know as you say if the carb blockage was making no 1 drag through its cycle, maybe dredge up some oil through the rings or down through the stem seals..... but i got my own oil leaks to worry bout

[andyb]

I wonder if it's a coincidence that the #1 cylinder was the one that appeared to be passing some oil into the exhaust.  Could the closed carb have done something weird to the vacuum in the cylinder while the rest of the motor was at high load/high RPM that could cause it to suck oil? 

High rpm with closed throttle blades (trailing throttle, usually) and/or a slide stuck firmly down would both give the same effect; very high vacuum on the intake cycle.  Valve seals are often weak link when it comes to handling that much vacuum, so not a huge surprise on greasing that hole.

[TheRadBaron]

That's pretty much what I was thinking.  I got the valves all taken out of the head and they all look very good.  There's some carbon on the intake valve seats that weren't closing all the way, but there is no visible pitting anywhere.  I'll be lapping them with some fine-grit lapping compound and I think that they'll be ready to go. 
The stock valve seals were not in good shape and looked to be a poor design to me.  I've got some replacements from Randy that will be going in soon.
I'm currently soaking the valve heads, combustion chambers, and ports with Sea Foam to soften up the carbon deposits before I attack them with a brass bristle brush.
I'm pretty pleased with the way everything is going so far.  Instead of one big problem with the motor that I had feared, it looks like it just had a few minor problems that will be (relatively) cheap and easy to fix.