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1973 Z1 Maui 29 Dec 2021 15:52 #859786

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It looks like the cam bearings had rotate and blocked the oil passage in the cam journal. Are the surface of the cam cap and head ok?
Could it be the cam cap didn´t match to the specific position or bearing clearance and build up to much friction/pressure?

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1973 Z1 Maui 29 Dec 2021 16:27 #859787

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Glad to hear you found the problem. That cam looks too nasty to have been damaged by the bearings.  I'm wondering if the cam didn't damage the bearings instead of the other way round?

Oil flow to the cam bearings is via two of the outer head studs.  It flows up the studs and into the galleries where it can enter the cam bearings.  If it looks like you were getting oil to the other bearings you might want to check the hole in the bearing seat to ensure it's clear.  You might even want to check all of them.

If you plan to check oil pressure you should get around 2.8 psi at 3,000 rpm, with 10-40 oil at around 140 F.
I have several restored bikes along with a 2006 Goldwing with a sidecar. My wife has a 2019 Suzuki DR 650 for on and off road.

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1973 Z1 Maui 29 Dec 2021 17:12 #859792

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That is a gnarly. That much damage from two short runs. Yikes! 
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1973 Z1 Maui 29 Dec 2021 17:25 #859794

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I removed the cylinders and I’m checking all oil passages. Ongoing. I’m going to make an adapter that attaches to the plug next to the oil pressure switch that I can use for:
hooking up an oil source to pre-charge the passages in the head up to the cams.
hooking up a temporary low pressure gauge to verify I have oil pressure at that point. To be easy to read I’ll get a 0 to maybe 10 pound gauge.
im it satisfied the oil pump purged up to the head.

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1973 Z1 Maui 29 Dec 2021 19:56 #859798

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If you find you have low oil pressure....just wondering if you remembered to put the o ring in place when you sealed the cases?  

Something I try to do is take a photo of every step of a rebuild.  This is one I took of an engine just before I sealed the cases.

 
I have several restored bikes along with a 2006 Goldwing with a sidecar. My wife has a 2019 Suzuki DR 650 for on and off road.
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1973 Z1 Maui 30 Dec 2021 06:43 #859809

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Z1 cam bushings are a steel shell supporting a thin layer of relatively soft bearing babbit as the oiled load bearing surface.  If the bushings truly 'spun', the bore surfaces in the head & cam cap that holds the bushing halves will be damaged by the steel shells.  The damage as pictured looks more like the cam seized in the bushing?  Did the bushings truly seize to the cam & rotate within the head/cam cap?  Maybe just a difference of nomenclature...

Are the bushings new OEM or the originals?  If the original bushings were reused, were they in the original positions?  Aftermarket? 

If we replace bushings with new ones, we always torque the cams into the head sans valves to make sure the cams spin freely.  Plasitigauge as called for in the manual if bushing clearances are in question.

It's difficult to tell with debris in the oil holes, but the oil holes look smaller than those in OEM bushings to our calibrated eyeballs. An OEM cam bushing is pictured below.  The hole measures 4.88mm (0.192 in.) dia.  Note the chamfer surrounding the hole.  The rear of the hole in the steel shell is also chamfered.  The bushing measures 1.52mm (0.057 in.) thick.  The distance between the edge of the hole and the edge of the bushing on either side is ~5.43mm (0.214 in.)  All measurements done with a digital caliper.


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1973 Z1 Maui 30 Dec 2021 06:49 #859811

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If we replace bushings with new ones, we always torque the cams into the head sans valves to make sure the cams spin freely.  Plasitigauge as called for in the manual if bushing clearances are in question.


I always check the cams spin free, plastic gauge also works.
Something was wrong here, hopefully head was not damaged.
 

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1973 Z1 Maui 30 Dec 2021 07:10 #859814

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All good information. Upon disassembly I didn't find evidence that the oil actually reached the head. It's as if the air could not get out. 
The bearings were new. 
I will be assembling the next new bearings without the valves installed to check.
I did not find any blockages.
The o ring between the cases was installed.
I do wonder about something. With this low pressure system, if the oil holes in the head are blocked by the journals resting over them and the air cannot escape, the pump might not be able to expel the air. I have ordered another plug that fits next to the pressure switch that I can make into a fitting so I can pre-charge the upper side of the oil system and purge most of the air out. This is on the "up" side of the pressure switch plunger which also seems to act as an anti drain back valve, it only has a tiny bypass hole in it.
The head is ok.

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1973 Z1 Maui 30 Dec 2021 07:24 #859815

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I do wonder about something. With this low pressure system, if the oil holes in the head are blocked by the journals resting over them and the air cannot escape, the pump might not be able to expel the air. I have ordered another plug that fits next to the pressure switch that I can make into a fitting so I can pre-charge the upper side of the oil system and purge most of the air out. This is on the "up" side of the pressure switch plunger which also seems to act as an anti drain back valve, it only has a tiny bypass hole in it.

The cam lobes push the cam shaft up, the pump will push the oil through.
The cam bearing caps are numbered 1,2,3,4 the head and caps were line bored together.
You had zero or negative clearance to cause this.
Remove valves, oil bearings, install cams, install caps, check that cams spin free.
 

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1973 Z1 Maui 30 Dec 2021 14:24 #859843

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Hi Maui, has this only affected the one Journal ? 
if it was a bigger oil supply issue I would have expected multiple journals to have been effected to a lesser degree, as opposed to the damage being localised
 
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1973 Z1 Maui 30 Dec 2021 17:50 #859851

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On the right side of the engine there is an access port to the main engine oil gallery feeding the head.  This is a much easier location to check oil pressure.

 
I have several restored bikes along with a 2006 Goldwing with a sidecar. My wife has a 2019 Suzuki DR 650 for on and off road.
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1973 Z1 Maui 31 Dec 2021 13:28 #859868

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It's after the fact, but one thing I was taught a long time ago was to always Plastigage bearings when building a motor.  Yes it takes a few extra minutes, but Plastigage is cheap and it can save you a lot more on the back end including sizeable amounts money.

Rick H.
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