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

[TheRadBaron]

I just brought home an '84 FJ with 51,000 miles.  The guy I bought it off of had it for a year or two and only put about 1000 miles on it.  The only maintenance he did on it was an oil change and new plugs when he got it.  Before that, it's maintenance history is unknown.
The guy told me that it had been running great until the last time he rode it a few weeks ago when it suddenly seemed to lose power.  He thought that it felt like it was only running on three cylinders.  He noticed that some oil was dripping from the exhaust collector (low point in the system) and that the #1 cylinder exhaust port area was all oily.  The assumption was that the plug had fouled due to the oil in the cylinder. 
However, once I got the bike home and did a compression check I found the compression low and all over the board.  There is a lot more wrong here than oil consumption.  Here's the readings that I got:
#1 - 90psi
#2 - 40 psi
#3 - 60 psi
#4 - 120psi
I tried pouring some 60wt oil into the cylinders and it had no effect on the compression so I assumed that the valves were the problem.  I pulled the cam cover to check the valves and discovered that on all four cylinders, ONE of the intake valves had closed up all the way so that there was no clearance at all.  The exhaust clearances were all okay, and the other intake valve on each cylinder was a bit tight but at least there was some clearance.  Strange.
Being the intake valves, the chances of burning a valve are a lot less than the exhaust valves due to the cooling effect of the incoming charge.  Still, I wonder why the clearance closed up like that on only one valve per cylinder and not the other, and whether I'll need to rebuild the head at this point.  Has anyone here seen this before?
Here's my plan for now:  I'll get one shim, the thinnest size available and use it to get measurements to (hopefully) bring all the valve clearances into spec.  Hopefully the valves/seats aren't burn and ruined and this will fix the compression problems.  Once the valves are right I'll try to run the bike and try to figure out the cause of the oil-in-the-exhaust problem.
Does this seem like a sound plan?  I'm new to this type of bike.  I'm used to early-'70s twins and singles with screw-adjustable valves.  Any advice or insight would be appreciated.  Thanks.

[TheRadBaron]

Actually, the more that I think about it, the more I think that I might go with a different approach.  I think that I'll just suck it up and pull the head off.  That way I can examine the bores, check the valves, lap or regrind them depending on their condition, check the valve guide clearance and correct if necessary, change the valve seals, and eliminate the head gasket as a potential source of the oil problem. 
Valve shims aren't cheap and they add up quickly when there's 16 of them.  I'd like to keep the swapping of them to a minimum.
Man, I'm used to singles and twins with two valves per cylinder (...or none at all.  I have a lot of 2-strokes).  Things are a lot cheaper when you aren't looking at 4 cylinders and 16 valves.  But they're a lot slower, too

[SlowOldGuy]

Did you have the throttle WFO when you were cranking it for the compression readings?

DavidR.

[TheRadBaron]

Yup, WFO to the max.

[Mark Olson]

in the first post , you mentioned maybe a plug had fouled . Was that the case?  I know you have bad compression but it is the all at once bad running thing that causes a problem.

If a plug fouled and caused the bad running then I could see resetting you're valve clearances and checking compression again, However if there was no bad plug then I think you are looking at a valve job.

when and if you tear it down check piston height on each cylinder , A bad fuel petcock can cause bent rods and a similar compression reading to what you have now.

[Dan Filetti]

when and if you tear it down check piston height on each cylinder , A bad fuel petcock can cause bent rods and a similar compression reading to what you have now.

This is good advice.  But to put just a bit of a finer point on it, it takes a bum petcock, (or one left on 'prime' -year depending-) AND one (or many) bad float needle seat o-rings which allow additional fuel passed once the bowl is full.  This allows the cylinder(s) to fill with excess fuel, and the rod to bend when you try to start it.

While you're at re-doing the top-end, order yourself one of David R.'s (OLDSLOWGUY) excellent stainless steel, allen-head screw and o-ring kits, and go through the carbs as well.  Sounds like it would not be an issue for you. 

Welcome here, by the way.

Dan 

 

[Harvy]

when and if you tear it down check piston height on each cylinder , A bad fuel petcock can cause bent rods and a similar compression reading to what you have now.

This is good advice.  But to put just a bit of a finer point on it, it takes a bum petcock, (or one left on 'prime' -year depending-) AND one (or many) bad float needle seat o-rings which allow additional fuel passed once the bowl is full.  This allows the cylinder(s) to fill with excess fuel, and the rod to bend when you try to start it.

While you're at re-doing the top-end, order yourself one of David R.'s (OLDSLOWGUY) excellent stainless steel, allen-head screw and o-ring kits, and go through the carbs as well.  Sounds like it would not be an issue for you. 

Welcome here, by the way.

Dan 

 

And maybe this confirms the above...... in the original post:

"He noticed that some oil was dripping from the exhaust collector"

I wonder if this was in fact fuel mixed with exhaust pipe carbon?


Harvy

[Dan Filetti]

And maybe this confirms the above...... in the original post:

"He noticed that some oil was dripping from the exhaust collector"

I wonder if this was in fact fuel mixed with exhaust pipe carbon?


Harvy

I wondered about that when I first read his post as well.   

Dan

[racerman_27410]

  But to put just a bit of a finer point on it, it takes a bum petcock, (or one left on 'prime' -year depending-) AND one (or many) bad float needle seat o-rings which allow additional fuel passed once the bowl is full.  This allows the cylinder(s) to fill with excess fuel, and the rod to bend when you try to start it.
Dan 

this would definitely explain the    "it was running fine right up until ... it wasn't"    statement


KOokaloo!

[TheRadBaron]

Thanks for the tips.  I sure hope that I don't have any bent rods...that would be stinky.  I have the head ready to pull at this point and I have a few theories that I need to investigate.  The oil in the header might be a partial fluke... the sump and oil cooler lines are leaking and I think that they were the origin of the oil leak my buddy identified.  There was a LOT of totally unburnt, clean oil in the header.  I think that what might be happening is oil leaking from the sump and cooler lines is getting into the header collector through a rust hole, maybe.  The collector area is really greasy and oily and covered in gravel and road bits.  I need to clean it off and take a look.  Still, there's evidence of some oiling from the #1 cylinder, though I don't think it's as severe as I first thought.  The plug that came out of that cylinder looked good, though I didn't check it for spark.
I really just need some time to work on the thing.  I should have enough time this holiday weekend to really get some answers.  I'll report back when I figure out more.

[Dan Filetti]

One more thing to check.  If you did flood a cylinder with fuel, then your oil would likely have a distinct smell of fuel.  Rings with 51,000 miles will allow some fuel by for certain.

If your oil does not smell like fuel, then the flooded cylinder idea may not be correct.

Just another thought.

Dan 

[andyb]

With the head off, you could probably measure how far the pistons are in the hole.  If there's one that's way off, start guessing at a bent rod.  Likely not though.

[SkyFive]

I had the valve problem you speak of. My valves were not seating but somehow the engine still ran. There was a thin layer of carbon on the valve seats and no clearance between the shim and lobe. I reworked the head and installed new exhaust valves then I fiddle farted around with the shims for a few hours before I finally took a measurement from the empty bucket to the cam lobe and realized my valve seats were worn out. I ended up replacing my cylinder head. If you need some thin shims let me know and we can do some trading.

[TheRadBaron]

Good news...I pulled the head off tonight and all the pistons have healthy and proper compression height.  Man, I am relieved.  Not only that, but the pistons and bores look astonishingly good for having 51,000 miles.  The crosshatch pattern in the bores is still clearly visible and there is no ridge at the top of the cylinders apart from a thin layer of carbon.
Is it normal for the bores to still show the crosshatching at this mileage?  Since the history of the bike is unknown, I suppose that it could have had top-end work done in the past.
At this point I feel pretty confident that the compression problems are due to the intake valves not closing completely.  This weekend I'll take the head apart and take a look at everything.  I'm hoping that a good lapping will set them right and the guides are in good shape and I can put the thing back together with some new valve seals. 
I sure am happy that the motor didn't have the dreaded hydro-lock bent rods.  I will sleep well tonight, dreaming of a healthy FJ.

[Harvy]

Good news...I pulled the head off tonight and all the pistons have healthy and proper compression height.  Man, I am relieved.  Not only that, but the pistons and bores look astonishingly good for having 51,000 miles.  The crosshatch pattern in the bores is still clearly visible and there is no ridge at the top of the cylinders apart from a thin layer of carbon.
Is it normal for the bores to still show the crosshatching at this mileage?  Since the history of the bike is unknown, I suppose that it could have had top-end work done in the past.
At this point I feel pretty confident that the compression problems are due to the intake valves not closing completely.  This weekend I'll take the head apart and take a look at everything.  I'm hoping that a good lapping will set them right and the guides are in good shape and I can put the thing back together with some new valve seals. 
I sure am happy that the motor didn't have the dreaded hydro-lock bent rods.  I will sleep well tonight, dreaming of a healthy FJ.

Well that's a load off your mind.

I remember Frank M telling very early in my ownership of the FJ that the cross hatching on the bores from the factory was pretty decent (for want of a better way of putting it). I believe he was quoting Hank Scott at the time.


Harvy