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FZ70 Disassembly

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Old 04-27-2012, 08:46 AM
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Four Stroker
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Default FZ70 Disassembly

Hey Petec;

I have the 70 totally disassembled and can't get the crank out. I baked it in the oven at 250F which usually gets the bearings to fall out. I suspect that the crank ring is running in a groove and I need to press the crank out gently. Can you give some advice on how to get the crank out ?
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Old 04-27-2012, 04:04 PM
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Default RE: FZ70 Disassembly

Heat only the outer engine block only with a covering heat gun at the highest setting.
As soon as its hot, grab it wit an oven glove and tap the back plate surface on some wood.
Should start to move after a few progressively harder raps on the wood.
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Old 04-27-2012, 04:37 PM
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Default RE: FZ70 Disassembly

Have you taken an engine apart with a crank ring ?
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Old 04-27-2012, 04:54 PM
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Default RE: FZ70 Disassembly

Several YS 1.40, 1.60, and 1.70. Never seen one with a groove from the crank ring.
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Old 04-27-2012, 09:10 PM
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Default RE: FZ70 Disassembly

Well I guess I need more heat. Is there a steel sleeve for the crank ring ? I don't see how aluminum could not wear a groove. Anyway, I'll get it apart and find out how it's made. Thank you for you reply.
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Old 04-28-2012, 07:27 AM
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Default RE: FZ70 Disassembly

When I run into a stubborn crank, a block of oak over the crank snout to keep from damaging the nut and a rawhide mallet for some light persuasion is my poison of choice. I'll put it in th elite toaster oven in my shop for a few minutes so the aluminum heats up bu thte steel don't really heat soak, pull it out and give it some taps. Welding gloves make this process much easier than using oven mitts.
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Old 04-28-2012, 12:01 PM
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Default RE: FZ70 Disassembly

Thanks Petec;

I have a 1 ton arbor press (hand operated) that I will use to gently persuade it to depart after I heat it up.

What is this crank ring coated with ? Looks like grey teflon or something. I am still trying to figure out how a steel ring runs in an aluminum case.
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Old 04-28-2012, 12:13 PM
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Default RE: FZ70 Disassembly

My guess is that the steel ring does not rotate, the crank just spins with the ring stationary.
The case is all aluminum with no insert.
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Old 04-28-2012, 01:08 PM
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Default RE: FZ70 Disassembly

That does sound very reasonable. The wear marks on the ring should tell us for sure. I will take some pictures and post them. I am always just curious how things work. I am probably replacing far more than I need to. What do you normally replace in a rebuild ?
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Old 04-28-2012, 04:45 PM
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Default RE: FZ70 Disassembly

What's the reason for the rebuild in the first place?
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Old 04-28-2012, 04:57 PM
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Default RE: FZ70 Disassembly


ORIGINAL: ThumbSkull

My guess is that the steel ring does not rotate, the crank just spins with the ring stationary.
The case is all aluminum with no insert.
+1....
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Old 04-29-2012, 07:37 PM
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Default RE: FZ70 Disassembly

I rebuilt the engine today. You guys didn't warn me that getting the crankshaft ring in would be the hardest part. I finally got it back in by forcing a small nylon wire tie down one side until it came out the other - between the ring and case. I'm getting about 8.5 PSI in the tank with the new ring. The pressure had dropped to about 6 PSI before the rebuild.

Reason for rebuild - serious sagging performance. I think just a piston ring and cleaning up the valves will be enough next time.
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Old 04-29-2012, 07:47 PM
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Default RE: FZ70 Disassembly

The larger engines have a chamfer that helps the ring compress to size on the way in.
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Old 04-29-2012, 07:52 PM
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Default RE: FZ70 Disassembly

There is a chamfer at the rear to get the crank out but I fear they didn't have room going forward - probably due to the bigger new angular contact rear bearing.


I tried taking some macro pictures but the shinny wear marks didn't come out well. Bottom line is that the crank ring doesn't rotate and only touches the crank on one side. It should never need replacing. When you put it back in, it self-adjusts the side gap. Worst case turn it around. The 70 is difficult to put back together if you want to replace the rear bearing.


The new angular contact combo radial and thrust bearing is interesting. Do the larger engines use this type of bearing ?
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