Cam install/Spring height/Rocker dilemma

[ozconnection]

Chances are they're not stock retainers. I'd say that because your thicker lash pads needed taller shoulders on the retainer to stop the pads from being 'spat out' like 1fastz said earlier.

 

Rip the head off and start fresh. You'll be able to finally see what that head is. We're all curious too.

 

A P90...with N42 valves, that's a possibility!

 

I wonder why the engine wasn't performing. Do you think it was the old cam?

[Babalouie]

I wonder why the engine wasn't performing. Do you think it was the old cam?

Yes I think so. The cam was huge: 278degs @50thou lift, 600 thou total valve lift. Pretty wild.

 

It would spit fuel out the carbs at idle and wouldn't make any power at all, and at 5000rpm it hits a wall and goes all breathless. The timing was out too, I measured it at a lobe centre (assuming it was half way between 50 thou lift on opening & closing) at 99IN/110EX, which can't be right.

 

Here's a closer pic of the old cam by the way, and how small the base circle is:

 

So the old cam was mis-timed and way too wild. But to no point on the rev range did it really take off, and for such a huge cam, it fell over completely at the top end. Sure the timing was out, but I didn't think 5 degrees would be that fatal to the power output. This was all really baffling, and also the valve train was always noisy as hell, so I assumed that there was something there that wasn't "happy".

 

Hence I decided to eliminate the cam as a source of the issues and swap in a known good hot street grind. The new cam is the "72 degree works rally grind" which is roughly equivalent to MSA Stage IV, and then reassess if the problems have gone away or not.

 

Other highpoints of the engine are: 190~200psi comp on all cylinders, great oil pressure, brand new electronic ignition system, new carbs, new manifold. In fact you can probably see from the interior of the head that the motor is actually quite fresh overall....I figured that weird cam was probably the source of the issues, but we'll have to wait a little longer to find out!

[Babalouie]

Ok the head is off now

 

I stripped off the carbs and manifolds the other day, and of course the radiator was removed a few weeks ago. Off come the head bolts, and the cam (although I think I didn't really need to take the cam out)...

 

And off the head comes! I've said before that I've suspected that the engine is quite freshly built, and certainly the head came off quite easy. Didn't have to prise it off or anything, it just lifted off the head by hand.

 

I've always suspected that the motor might be a 3.1L, and I think the L3.1 stroker theory may have gained a bit more credence too. Stock L28 bore is 86mm, and as part of the 3.1L conversion you bore it out 3mm. My bore measured at 89mm, so assuming the crank is a stock L28 item, the capacity will be about 2950cc. You need the stroker crank to bring it another 150cc, and I dunno if I have that or not.

 

I have wedged in the chain, etc and so I'm a little gunshy about turning the crank in case the tensioner pops out....but I'm sure there is a way of measuring it (is there?). In terms of wear, there is that spot on the far side of the bore which is a little scuffed, and you can barely see the cross hatch pattern from the honing, but given the great compression figures I guess it's not a problem. Bores aren't lipped either so wear seems to be ok, although I would feel better if there weren't so many vertical wear marks....

 

Pistons are flat tops, zero deck height.

 

The head as I said came off easily, in fact it popped off the block on its own while I was messing around with removing that coolant hose that goes to the back of it.

 

Based on the combustion chamber shape, I think it might be the later-P90A head as suspected, but it kinda looks like there's been a lot shaved off it for more compression?

 

Valve sizes are 37mm EX

 

...and 45mm IN. So I think that yes, Naviathan was right in that they are older/larger N42 valves from the late 70's L28, which does now confirm why the valves are so tall

 

And that's where we are! I'd love to find a way of measuring the stroke, without upsetting the chain, and I'm sure there is a way, but it seems that it's definitely been given a 3mm overbore

 

But it seems that the tall-valve theory is on the money, so it's now over to the pro engine builder for sorting

[TimZ]

And that's where we are! I'd love to find a way of measuring the stroke, without upsetting the chain, and I'm sure there is a way, but it seems that it's definitely been given a 3mm overbore

 

It seems to me that you are so far into it now that pulling the front cover and not worrying about the chain is an extra 15-20 minutes worth of work. Take the chain off and turn the crank at will.

Once you get the head back you are gong to want to degree the cam in properly anyway right?

[Babalouie]

It seems to me that you are so far into it now that pulling the front cover and not worrying about the chain is an extra 15-20 minutes worth of work. Take the chain off and turn the crank at will.

Once you get the head back you are gong to want to degree the cam in properly anyway right?

Is there any special trick/tips to getting the crank pulley bolt undone?

 

And yes I have a degree wheel all set up to dial the cam in properly anyway.

[TimZ]

Is there any special trick/tips to getting the crank pulley bolt undone?

 

And yes I have a degree wheel all set up to dial the cam in properly anyway.

 

Impact wrench.

 

Then use a gear or pulley puller to get the pulley itself off.

[1 fast z]

Yep, just as I suspected. Pistons are very custom.

[ozconnection]

Try putting the trans in 5th and chock the wheels with the hand brake on.

 

Or you can use a long braker bar, lean it against a solid part of the car with a rag in between or on the road and bump your starter motor.

 

I've tried both methods and they work as I didn't have an impact wrench at home at the time.

 

Judging by that last lot of photos, that was a built engine alright! Yeah, so long as the compression figures are all about the same, I wouldnt worry too much about the bores.

 

Good luck mate.

[SHADY280]

heres one for you guys, my engine has a p79 head, i milled it the .080" and to make up for the gap i used my n47 head valves which are 1/8" longer. it worked properly only because my valve train was shimmed up .080" to compensate. so my lash worked properly with slightly thicker lash pads for the re-ground cam.

[Daeron]

Could that be the Maxima N47 head? (I forget what the exhaust ports are on that one) Barring that, I agree with the P90 argument, unless it is some Non american market head.

 

*I* want to know what your original camshaft was ground for... At this point I am betting you've got a full stroker motor (those pistons ARE very nice looking ) and I would imagine that such a narrow lobe, that ramps up so high, would be laborious for that engine to run on.. I wonder what that skinny cam would do in an L24 with a valvetrain to run up to 7500 every time and some triple 40's with narrow chokes would sound like.......

[Babalouie]

*I* want to know what your original camshaft was ground for... At this point I am betting you've got a full stroker motor (those pistons ARE very nice looking ) and I would imagine that such a narrow lobe, that ramps up so high, would be laborious for that engine to run on.. I wonder what that skinny cam would do in an L24 with a valvetrain to run up to 7500 every time and some triple 40's with narrow chokes would sound like.......

Well funnily enough, like I said, the old cam just hit this brick wall at 5000rpm. It was not dialled in correctly so possibly that had something to do with it, but it did sound like the valvetrain was hurtin'...a lot. It was very thrashy sounding, even at idle. And with the rockers in place the engine was very stiff to turn by hand.

http://au.youtube.com/watch?v=jPy4JcOcLxM

[Daeron]

Well my thinking is that the camshaft could be one of three things:

 

Improperly Dialed In;

Improperly matched to your stroker motor/carb tune;

A Piece Of Worthless Junk; An Anti-Theft Device (hefty club, *bludgeon*)

 

My guess is the second one; hence me reaching for the opposite of a stroker (L24) and wondering if it would be happier with that. Some small venturis, some rich jets, some high compression, and some octane, I think that cam might be more than a funky baseball bat.

[Babalouie]

Well my thinking is that the camshaft could be one of three things:

 

Improperly Dialed In;

Improperly matched to your stroker motor/carb tune;

A Piece Of Worthless Junk; An Anti-Theft Device (hefty club, *bludgeon*)

 

My guess is the second one; hence me reaching for the opposite of a stroker (L24) and wondering if it would be happier with that. Some small venturis, some rich jets, some high compression, and some octane, I think that cam might be more than a funky baseball bat.

 

I think that the appearance of that cam is a little deceiving....the base circle is so small, that it looks pointy and skinny, but I think in reality it's a lot fatter and matchbox-shaped than meets the eye. A hi-winding L24 is an interesting idea, but then again how would an L24 cope with a whole 600 thou of valve lift?

 

As for your mismatch theory, I'm running 32mm chokes on Weber 40s, so yes, the opposite of what you need for a hi-rpm screamer, so that's got to be a factor too.

 

But anyway, it's destined to be hung up on the garage wall with a suitable plaque along the lines of "JDM CAM OF FAIL" under it

[Daeron]

I'd keep it between my driver seat and the center console for use as a theft-deterrent. Maybe a little grip tape on one end, and an old timing gear on the front

[Babalouie]

I'd keep it between my driver seat and the center console for use as a theft-deterrent. Maybe a little grip tape on one end, and an old timing gear on the front

Actually I plan on sending it back to Japan, to the dealership that sold me the car (200hrs and 10mths later...still not roadworthy) with some self-explanatory instructions on what they can do with it

[ozconnection]

I have found that a few times with reground cams. They're noisy!! As your youtube video is testament. Doughey throttle response too if you don't mind me saying. For that combo, theoretically, it should be very 'snappy' but sadly it isn't. But it soon will be, hey!

 

I suspect it something to do with the ramps being poorly designed or the recommended lash being all wrong.

 

JM might be able to do something with it...he loves 'em big and lumpy

[Daeron]

I suspect it something to do with the ramps being poorly designed or the recommended lash being all wrong.

 

JM might be able to do something with it...he loves 'em big and lumpy

 

Yuk @ end comment..

[(goldfish)]

If one piston is @tdc then one piston is @BDC right? Measure the difference.

[2eighTZ4me]

Could that be the Maxima N47 head? (I forget what the exhaust ports are on that one) Barring that, I agree with the P90 argument, unless it is some Non american market head.

 

It's definitely NOT a MN47 head. They had round exh. ports with liners, and 42mm x 35mm valves. I tried going with 44's and 38's on my MN47, and it couldn't be done with out some real expensive machine work. The seats would overlap. I suspect P90 as well, but I also didn't get a good close look at the exhaust ports (covered with soot where the header sat). The P90 has somewhat hexagonal shaped exh. ports. An N42/E31/E88 will have true rectangular ports. Again - could be a non-American head as you say that we in the States have not come across before!

 

That is one hell of an asymmetrical cam you have pictured there.

 

As for the stroker theory - since Bryan noted those are indeed custom pistons (not a standard "flat-top") - there is a distinct possibility they are custom made forged pistons that have a "corrected" pin height measurement. On a standard stroker build, at TDC, you have about .6mm of the piston sticking up out of the block. Yours look flush to the block in the pictures (not knowing if the motor is at TDC though...) Only way to know for sure with yours is to get one piston at BDC, and measure the depth from the top deck of the block to the top of the piston. If it's 79mm, you have a standard crank. If it's 83mm, you have the LD28 crank. If it's neither of the two - you have one heck of a custom motor that I'd like to find out more about!

[BRAAP]

If one piston is @tdc then one piston is @BDC right? Measure the difference.

 

That would hold true for a V-8 or 4 cylinder, but not a 6 cylinder. most 6 cylinders, (all Datsun/Nissan L-6's) crank throws are 120 degrees apart. The pistons travel in unison in pairs. 1-6, 2-5 and 3-4. In the 4 event cycle, these paired pistons are in the opposite event from each other, i.e. if one is compression, the other is exhausting. If one is on the intake, the other is on the power stroke.

 

At any rate, with 2 pistons at TDC the other 4 pistons are at the same distance down the bore, not quite at BDC. 2 are on the way up, the other 2 on the way down.

 

This illustration shows typical inline 6 cylinder crank-pin lay out.