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Author Topic: Fixing A 86 FJ1200 with bad compression on #3 cyl.  (Read 13774 times)
Mark Olson
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« Reply #15 on: January 22, 2019, 08:48:37 PM »

It has been determined that my piston lands were cracked from poor rebuild methods.
So 20k ago when the PO had the bent rod fixed and they reringed the Pistons and rebuilt the head, they screwed up and cocked the 2_3 Pistons upon install and cracked the ring lands.

It's kinda amazing the engine ran for 20k before finally craping out.
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Mark O.
86 fj1200
sac ca.

                           " Get off your ass and Ride"
Tuned forks
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« Reply #16 on: January 22, 2019, 10:28:15 PM »

Shows how tough that lump of aluminum is.

Joe
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FJmonkey
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« Reply #17 on: January 22, 2019, 11:22:36 PM »

It's kinda amazing the engine ran for 20k before finally craping out.

20K of your flogging it like it owed you money.  mad That's like "Dog Years"

But I know you love it, you slid under your FJ when it lost traction.  blush
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ribbert
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« Reply #18 on: January 23, 2019, 07:24:39 AM »

It has been determined that my piston lands were cracked from poor rebuild methods.
So 20k ago when the PO had the bent rod fixed and they reringed the Pistons and rebuilt the head, they screwed up and cocked the 2_3 Pistons upon install and cracked the ring lands.

It's kinda amazing the engine ran for 20k before finally craping out.

Who made that determination? That would be uncommon for pistons fitted from the bottom.

Mark, you allude to the fact you ride it hard, how high do you rev it when flogging it?

Noel
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FJ_Hooligan
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« Reply #19 on: January 23, 2019, 10:38:05 AM »

Noel,
It's very easy to screw it up if you don't use ring compressors. 

I've seen people try to install the pistons without using one.  They compress the rings by hand or use a screwdriver. 

Some are successful, some are not.  The unsuccessful ones usually (unknowingly) break a ring or crack the ring land.
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DavidR.
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« Reply #20 on: January 23, 2019, 04:19:10 PM »

Yea, along with not clocking the ring gaps correctly or installing the #2 compression ring upside down can cause grief.

I’m surprised with the piston damage, the cylinder walls were not affected.
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ribbert
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« Reply #21 on: January 24, 2019, 07:44:12 AM »

Noel,
It's very easy to screw it up if you don't use ring compressors. 

I've seen people try to install the pistons without using one.  They compress the rings by hand or use a screwdriver. 

Some are successful, some are not.  The unsuccessful ones usually (unknowingly) break a ring or crack the ring land.

I had read it as a cracked piston. Having a ring compressor is no guarantee of not screwing it up either, I've seen plenty, however a large tension wrench in the hands of someone with a workshop manual and no "feel" does the most damage.

Noel
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FJ_Hooligan
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« Reply #22 on: January 24, 2019, 08:09:33 PM »

….a large tension wrench in the hands of someone with a workshop manual and no "feel" does the most damage.


So so true.  I know many of those types.  Like handing a baby a loaded gun.

They are usually the ones that ask for the torque on every single fastener.  I'll use a torque wrench on engine components (head bolts/nuts, cam/crank/rod caps, etc), brake calipers and axles.  Just about everything else gets torqued by hand.  Always been a bit hesitant about using a torque wrench on small(ish) fasteners in aluminum.
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DavidR.
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« Reply #23 on: January 24, 2019, 10:25:00 PM »

Yep especially when one is armed with a cheap torque wrench. Would you believe I once tried to torque the little bolts on the clutch. Well I only needed the sheered bolt head off the first one to stop me trying the others that is. Live and learn.
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Mark Olson
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« Reply #24 on: January 25, 2019, 11:14:47 PM »

It has been determined that my piston lands were cracked from poor rebuild methods.
So 20k ago when the PO had the bent rod fixed and they reringed the Pistons and rebuilt the head, they screwed up and cocked the 2_3 Pistons upon install and cracked the ring lands.

It's kinda amazing the engine ran for 20k before finally craping out.

Who made that determination? That would be uncommon for pistons fitted from the bottom.   i did after my research.

Mark, you allude to the fact you ride it hard, how high do you rev it when flogging it?   all the way to the rev limiter

Noel

 Hey Noel , long time since I heard from you . How Ya been?

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Mark O.
86 fj1200
sac ca.

                           " Get off your ass and Ride"
Mark Olson
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« Reply #25 on: January 25, 2019, 11:24:09 PM »

Yea, along with not clocking the ring gaps correctly or installing the #2 compression ring upside down can cause grief.

I’m surprised with the piston damage, the cylinder walls were not affected.

well pat , that is because of the oil I used.   AMSOIL   blum1
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Mark O.
86 fj1200
sac ca.

                           " Get off your ass and Ride"
Mark Olson
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Forum Member #16


« Reply #26 on: January 25, 2019, 11:32:06 PM »

It's kinda amazing the engine ran for 20k before finally craping out.

20K of your flogging it like it owed you money.  mad That's like "Dog Years"

But I know you love it, you slid under your FJ when it lost traction.  blush

Monkey , I did not realize those were dog years ... and of course I love my FJ enough to protect it from hitting the ground.  crazy
maybe it is time for case guards.
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Mark O.
86 fj1200
sac ca.

                           " Get off your ass and Ride"
Mark Olson
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Forum Member #16


« Reply #27 on: January 25, 2019, 11:36:00 PM »

….a large tension wrench in the hands of someone with a workshop manual and no "feel" does the most damage.


So so true.  I know many of those types.  Like handing a baby a loaded gun.

They are usually the ones that ask for the torque on every single fastener.  I'll use a torque wrench on engine components (head bolts/nuts, cam/crank/rod caps, etc), brake calipers and axles.  Just about everything else gets torqued by hand.  Always been a bit hesitant about using a torque wrench on small(ish) fasteners in aluminum.

So true .. I am with you on that.
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Mark O.
86 fj1200
sac ca.

                           " Get off your ass and Ride"
Mark Olson
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« Reply #28 on: January 26, 2019, 08:53:41 PM »

I picked up some donor pistons today. Now I just have to check them out.  yahoo
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Mark O.
86 fj1200
sac ca.

                           " Get off your ass and Ride"
Mark Olson
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« Reply #29 on: August 23, 2019, 12:11:26 AM »

Hey guys, update on my FJ .
The cylinder was scored and after a hone job to clean it up the clearance was past limits.  negative

I remembered talking with George Bowers about Kim and Steph having some FJ engine parts gathering dust since he quit riding.
Yes some of you may remember who I speak of.

Turns out they had a 1100 cyl bored out to standard 1200, Pistons custom fit to each bore , Rings , wrist pins, clips, gasket set , o-rings ETC.
Everything I needed to put my engine back together.
So this weekend is wrenchapolusa  good2
If all goes well I will ride sunday.

I will take pics .... Maybe
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Mark O.
86 fj1200
sac ca.

                           " Get off your ass and Ride"
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