snapped cam

[datsunaholic]

A fracture in the very center of the cam is almost always a warped head. If you blew the gasket between #2 and #3 from a broken radiator, that head is warped. Someone didn't properly check flatness. If you overheat enough to blow a gasket that way the head had to warp. Otherwise the gasket wouldn't blow into the cylinders- the fire rings in the head gasket are designed to withstand far more pressure than you can ever get in the cooling system.

 

Another way to fracture a cam in the middle is if the head bolts were tightened without going in stages. That'll warp the head too. Going full torque on the middle 2 bolts without the rest done in stages pulls the middle of the head down like a V.

[docbainey]

 

I've pulled lots of valve covers off and never seen one so dry. Usually it's swimming in oil.

 

 

Isn't the cam usually filled with oil??? Wouldn't it at least be wet???

 

I agree with Mike, at the least there should be oil in all the socket head cap screws (head bolts), unless yor parking this thing at a 90deg angle.

[72240z]

Ya but its internally oiled how would it get there? The dimple on the cam follower in front of the lobe where the oil comes out has oil in it.

[Rays74]

Line honing, even the slightest, will remove metal......which in turn means the cam bearings will now be that much (even slightest) oversize with no way to bring back to correct tolerance.

Nope :sick:.

You CAN make/use a tool that mimic's the cam in size and shape to check the towers for concentricity, but never use ANYTHNG that would do ANY cutting of the aluminum. :thumbup:

[banzai510(hainz)]

My head was warped and I had to have the TOP milled also.

I didnt want to remove the towers but it had to be done.

I have had 2 heads done and my first head the guy took off the towers also. I was pissed. I know the book says dont. The machinst didnt want to work around the towers on this head. But it went back together OK.

 

head#2

I put in a cam and the very rear would not line up.Thus taking it to a machine shop.

getting the top and bottome cut and getting soem cam tower shims. Sealed Power makes them. Just put Datsun in the blank and it will come up.

 

I put the cam towers on VERY loosely and put the cam in(with oil in towers) and gently torq them down to spec. If cam can spin with your fingers that the best. If cam still spins by having the cam sprocket and you can turn it by hand I say fuck it and call it good. Install the rockers and run it.

[I'm BLUE]

Thankyou 72240z and Rays74 .. I'm glad I'm not the only one afraid to remove cam towers without consequences or trade-off's ( I did not because FSM told me not to lol )

 

I can appreciate the fact when one must have to or should which happens quite a bit.

 

Heads can still be warped after machining gasket surface ... it happens ... seen it on other cars ... ( a good Machine shop pro-claimed it years ago )

 

EDIT : Just saw hainz reply this as my computer was slow. doh !!!

[banzai510(hainz)]

Yeah I installed my shims as the head was shaved .030 and installed 2 .015 shims.

cam would turn if I had my hand on the sprocket and turned it. Figired it would wear in. As the 4th cam tower was from another motor. So it wasnt a complete same set.

 

60K miles later its still running

 

as for the cam towers they are the bearings. So I assume you woundnt want to enlarge them anymore

[Fire-Kid]

My question jerry, is for 72240z.

Soo tell me you slept with your grandma just because you wanted an uncle? Lol

but joking aside i ask, are you a machinest, or have you at least talked to a machinest who says what your stating is correct?

I have built several engines up to and including 1700hp blown aluminum v8's but i havent had The chance to build a L series (but very soon). From my opinion i would say your best to surface The top and bottom of The head and cut The caps as needed and shim. Again this is an opinion we all have them same with you. Now lets try and help!!!

[72240z]

My question jerry, is for 72240z.

Soo tell me you slept with your grandma just because you wanted an uncle? Lol

but joking aside i ask, are you a machinest, or have you at least talked to a machinest who says what your stating is correct?

I have built several engines up to and including 1700hp blown aluminum v8's but i havent had The chance to build a L series (but very soon). From my opinion i would say your best to surface The top and bottom of The head and cut The caps as needed and shim. Again this is an opinion we all have them same with you. Now lets try and help!!!

 

WTF are you talking about? Im either too young or my neck isnt red enough to get that saying lol

I'm not a machinist, I'm a mechanic, but one doesnt have to be either to read a fsm.

I didnt make this shit up nor do I care who believes in it. Whats the argument anyway? That you guys all know more then Nissan engineers? Come on now....

As a professional I follow the factory procedure and specs at hand. Everyone else is welcome to do things their own way. It may work it may not again IDC, was just brainstorming on why this guys cam snapped and towers being out is an options for sure.

 

Line honing, even the slightest, will remove metal......which in turn means the cam bearings will now be that much (even slightest) oversize with no way to bring back to correct tolerance.

Nope :sick:.

You CAN make/use a tool that mimic's the cam in size and shape to check the towers for concentricity, but never use ANYTHNG that would do ANY cutting of the aluminum. :thumbup:

 

There is a tolerance for the cam bearings/journals and the head can be line honed multiple times before being outside of said tolerance (depending on care and mileage). The amount of material removed from a competent machinist is minute on the border of non existent, easily compared to standard wear.

 

What would one gain making a tool to mimic a cam when you could just use a cam? Moreover how is that in any way different then using a cam like some members do? Concentricity is not the only dimension that needs checking......

 

 

 

 

 

ANNNNNYYYYWAYYYYYYYYY

I still say the head needs to be checked to see if it was warped. Did we ever find out why the head gasket went after the last time?

Wonder if the cam could be JB welded together while in the towers and then checked for run out with a dial gauge.

Would bet either the head or cam is going to fail straightness tests.

[Rays74]

There is a tolerance for the cam bearings/journals and the head can be line honed multiple times before being outside of said tolerance (depending on care and mileage). The amount of material removed from a competent machinist is minute on the border of non existent, easily compared to standard wear.

 

What would one gain making a tool to mimic a cam when you could just use a cam? Moreover how is that in any way different then using a cam like some members do? Concentricity is not the only dimension that needs checking......

 

 

 

 

 

ANNNNNYYYYWAYYYYYYYYY

I still say the head needs to be checked to see if it was warped. Did we ever find out why the head gasket went after the last time?

Wonder if the cam could be JB welded together while in the towers and then checked for run out with a dial gauge.

Would bet either the head or cam is going to fail straightness tests.

 

As a long time wrench on many many of these types of OHC alloy plain cam bearing top ends, I've never seen a tolerance like you're describing Z..........got any spec or machining dimensions?? I wouldn't believe any exist but I am a humble man :)

The tool is a better substitute since there would be so much less chance of it being out of round compared to just using a random camshaft. Granted making or having the tool made may not be cheap, but a warped upper head or otherwise substandard tower assy may be caught earlier than later :)

On the other hand, in the half dozen L16-18-20 heads I've pulled and had rebuilt......all have had their cam tower's pulled before machining, all had their lash pads and assy's checked and all have gone on to live happy +50k mile lives. Before any of this though, the towers were bolted back on and the cams inserted with a drop of lite machine oil and spun........any binding would've raised a red flag, none did.

 

--Ray

[datzenmike]

Line honing, even the slightest, will remove metal......which in turn means the cam bearings will now be that much (even slightest) oversize with no way to bring back to correct tolerance.

Nope :sick:.

You CAN make/use a tool that mimic's the cam in size and shape to check the towers for concentricity, but never use ANYTHNG that would do ANY cutting of the aluminum. :thumbup:

 

About the only safe way, would be to throw away the ones you take off and install new un-cut towers. Have the head torqued down and align bore them. As Hainz says the towers ARE the bearings so cutting them would be a bad thing.

[Sealik]

....all have had their cam tower's pulled before machining, all had their lash pads and assy's checked and all have gone on to live happy +50k mile lives. Before any of this though, the towers were bolted back on and the cams inserted with a drop of lite machine oil and spun........any binding would've raised a red flag, none did.

 

--Ray

 

^^^^ exactly

[I'm BLUE]

I feel like such a noob again ... :lol:

 

Good thing I'm aware of most of this and at the same time just to chicken to try again on my stuff :lol:

[skyknight789990]

I agree with Mike, at the least there should be oil in all the socket head cap screws (head bolts), unless yor parking this thing at a 90deg angle.

there is no oil in the socket caps because i had just redid the head gasket before finding out my cam was snapped

[datsunaholic]

You did the head gasket and didn't notice the cam was broken?

 

The sockets will fill with oil in about 120 seconds of running over 2000RPM. There's supposed to be a LOT of oil flung up there.

[Uber Deaf One]

there is no oil in the socket caps because i had just redid the head gasket before finding out my cam was snapped

 

How did you not notice the broken cam when you did the head gasket?

[skyknight789990]

You did the head gasket and didn't notice the cam was broken?

 

The sockets will fill with oil in about 120 seconds of running over 2000RPM. There's supposed to be a LOT of oil flung up there.

i know this but when i was trying to find out my problem to my truck not running right i was checking the timing marks an tdc to see if it was right then seen the cam