I have a 88 suzuki samurai 1.3L had a blown head gasket, I replaced the head gasket and sent the head out to be reworked , I put back together. it run for about 75 mile and locked up the cam, I then replaced the head with a 1.6liter head and put a mech oil pressure gauge on it , it was reading 65psi when it first started , hot 43 to 54psi, it ran about 50 miles and again locked up the cam again . help do i have a bad oil pump?

I would guess you're putting the head gasket on incorrectly - there is a very small oilway near the front of the head that feeds the cam gear - put the gasket on backwards and upside down and everything lines up - EXCEPT - that oil way is blocked.

gasket was on correctly, have the Samurai Maintenance Manual,so was double checking everthing. both times, no blockage in the block , because had the head off and crank motor over and oil pumped out the oil hole on top of the block in front right side. that what has puzzled with whats wrong. anyother ideals , thanks

Dude, hate to tell you this, but it really sounds like the head gasket
was put on wrong. Find that hole in the front of the block, and make
triple dang sure the hole in the head gasket is also matched up with
it.

You should probably replace the oil pump if the pressures are that low,
my best guess is the over pressure relief valve is stuck open, I had that
happen to me once and blew the turbo up in Moab 

The engine will run with that low of pressure, but it's out of range and
it would best be taken care of now while the engine is sort of apart.

 
Good Luck
Wild

Well - I've given you the most common reason for that to happen.

The most common reason for a seized camshaft on a G-series engine is a lack of lubrication to the head, caused by some sort of a blockage of that oilway, and the most common cause of that oilway being blocked is the head gasket being installed correctly.

You say you turned the engine over with the head off and had oil flow, so it sounds like there's no blocakge in the block, you've had it happen to two heads, the chances of both heads having blockages is slim - reassemble, and this time turn it over with the head on and gasket in place, but with the cam out and make sure you have oil flow through to the cam gear.

There are a couple of other possibilities - excessive clearance in the bearings can cause excessive oil flow through those bearings causing starvation to other bearings and I have been told that that can happen with the cam journals.  Excessive clearance in the mains & big-ends can cause reduced pressure and starvation to the cam gear and although the oil pressures you have provided lack the details, at a glance they look fine, suggesting the bearings should be OK.

You have the FSM so you can check my memory - oil pressure is specified as 42~60 |removethispart|@ 3000 rpm at running temperature.

Oil pressure , the engine only needs 10 lb preasure per 1000 rpm to live,

Oil pressure , the engine only needs 10 lb preasure per 1000 rpm to live,

I'd like my engine to do more than barely survive, thank you.

Personal experience has shown that, even on an engine in dire need of a rebuild, 20 psi at a warm (800 rpm) idle is about normal - if you're only seeing 10 psi/1000 rpm, I'd suspect you're using too thin an oil, or that engine has significant wear.

This is must of what happened to mine. Blew a head gasket, I took it all apart and replaced the gasket. Seemed idiot proof, but drove it about 100 miles and cam siezed.