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Discussion Starter · #1 ·
It was a cold afternoon and I just started home from work in my'73 240Z. I don't have the chokes hooked up on my Weber DGV's so I'm revving the engine pretty much. The car had been running about 3 minutes and I was accelerating. All of a suddon, my revs wouldn't come down! the engine raced for a few seconds. I turned the car off and pulled off the road. apparently a hose had interfered with my return spring. I moved it and everything worked fine. I got back in and the car started fine and seemed to run good, except it was billowing white smoke out the exhaust! I only live about 5 miles away so I'm nursing it home. It is running fine and theres plenty of oil pressure but it continues to smoke. After about 3 miles, the smoke dies down but the car is very hot. I nurse it home. The temp gauge is almost to the top. I immediately think, blown headgasket. I check the oil and it is very full and foamy white (antifreeze I believe). I pull it into the garage and do a compression check. A couple of cylinders 2&6 are about 20 lbs under the others, but all have at least 100lbs of pressure. tonight I tear down the top end and find two things. 1. The headgasket does not have any real evidence of being blown. 2. the surfaces of the head and the engine both are gritty like sand. It cleans off, but I've never seen anything like this before. Tomorrow I plan to get a new head gasket and with proper cleaning put it back together. AM I MISSING SOMETHING? SHOULD I CHECK SOMETHING ELSE?? WHAT DO YOU THINK?? thanks. Bill
 

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If I were you, I would take the head to a local machine shop and have it pressure checked. It only costs about $30 and it is cheap insurance that the head is not cracked. I am working on a '78 280Z right now that we thought was a blown head gasket after doing a leakdown test. After removing the head, there were signs of a blown head gasket. No problem, so I thought. I took the head in for a valve job and the machine shop found cracks in 2 of the combustion chambers. I hope that this is not the case for you, but it would be a good idea to check it out anyway. Also, inspect the block for cracks. This is extremely rare on Nissan L motors, but it does happen. I don't think you should go to the trouble of having it magnafluxed, just give it a good look. Also, check the water jackets in the intake manifold around the carbs. You may have a leak there. BTW, get that hose out of the way of that return spring permanently!!! Good luck!!!

Ian
 

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> It was a cold afternoon and I just started
> home from work in my'73 240Z. I don't have
> the chokes hooked up on my Weber DGV's so
> I'm revving the engine pretty much. The car
> had been running about 3 minutes and I was
> accelerating. All of a suddon, my revs
> wouldn't come down! the engine raced for a
> few seconds. I turned the car off and pulled
> off the road. apparently a hose had
> interfered with my return spring. I moved it
> and everything worked fine. I got back in
> and the car started fine and seemed to run
> good, except it was billowing white smoke
> out the exhaust! I only live about 5 miles
> away so I'm nursing it home. It is running
> fine and theres plenty of oil pressure but
> it continues to smoke. After about 3 miles,
> the smoke dies down but the car is very hot.
> I nurse it home. The temp gauge is almost to
> the top. I immediately think, blown
> headgasket. I check the oil and it is very
> full and foamy white (antifreeze I believe).
> I pull it into the garage and do a
> compression check. A couple of cylinders 2&6
> are about 20 lbs under the others, but all
> have at least 100lbs of pressure. tonight I
> tear down the top end and find two things.
> 1. The headgasket does not have any real
> evidence of being blown. 2. the surfaces of
> the head and the engine both are gritty like
> sand. It cleans off, but I've never seen
> anything like this before. Tomorrow I plan
> to get a new head gasket and with proper
> cleaning put it back together. AM I MISSING
> SOMETHING? SHOULD I CHECK SOMETHING ELSE??
> WHAT DO YOU THINK?? thanks. Bill
Bill,
i had a similar problem on my 240 and also thought it was the head gasket. after i tore the thing down and put a new gasket in, i still had peanut butter for oil. it turned out to be the timing chain cover. you need to check and make sure it hasn't corroded causing a hole between the coolant passages that travel to the water pump and the timing chain case. this could likely be the cause of your problem, as the cover is aluminum and can corrode if you(or someone before you) hasn't used distilled water in your coolant mixture. even the smallest hole will make for big problems when the coolant is under pressure, and the size of it will increase rapidly, so check it thouroughly. if it is the problem, i would recommend spending the extra on a new cover, as used ones could already have the same problem. hope this helps
andy
 

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Discussion Starter · #4 ·
> Bill,
> i had a similar problem on my 240 and also
> thought it was the head gasket. after i tore
> the thing down and put a new gasket in, i
> still had peanut butter for oil.
> it turned out to be the timing chain cover.
> you need to check and make sure it hasn't
> corroded causing a hole between the coolant
> passages that travel to the water pump and
> the timing chain case. this could likely be
> the cause of your problem, as the cover is
> aluminum and can corrode if you(or someone
> before you) hasn't used distilled water in
> your coolant mixture. even the smallest hole
> will make for big problems when the coolant
> is under pressure, and the size of it will
> increase rapidly, so check it thouroughly.
> if it is the problem, i would recommend
> spending the extra on a new cover, as used
> ones could already have the same problem.
> hope this helps
> andy
Bill, In addition to the good advise that you have already received, at this point I would also consider a complete valve job if your budget allows it. This would include checking the head surface to insure it isn't warped. Then, make sure that you use a good torque wrench when putting the head back on - there is no substitude for it. Let us know how you make out.
 

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Discussion Starter · #5 ·
I have a explanation.
I think it's a bad Z. You need to buy a GOOD one.
thank you for your time.
Some more excillent advice....
lucky charms are good in the cold mornings!
-Professor Z...
 

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Discussion Starter · #6 ·
I have a explanation.
I think it's a bad Z. You need to buy a GOOD one.
thank you for your time.
Some more excillent advice....
lucky charms are good in the cold mornings!
-Professor Z...
 

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107,695 Posts
Discussion Starter · #7 ·
I have a explanation.
I think it's a bad Z. You need to buy a GOOD one.
thank you for your time.
Some more excillent advice....
lucky charms are good in the cold mornings!
-Professor Z...
 
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