Cam Wear?

[grannyknot]

All of the lobes on my cam are perfect and smooth except for the exhaust lobe on the #5 cylinder. I have had this engine for about 5,000 miles now and I don't think this has gotten any worse but not completely sure.

When I drag the edge of a razor blade over the lobe I can feel the roughness but still not sure if it is gouged into the cam or transfer from the rocker on top of the lobe.

What do you guys think?

Thanks,

Chris

[siteunseen]

Looks to me like the rocker arm is deteriorating.

[djwarner]

An old machinist's rule is that if you can't detect surface defects with your finger nail, it is less than 0.001" deep. Another method is to use a ball point pen nib across the marks for the same results.

 

Assuming you can't feel anything on the cam or rocker arm, I'd hit the rocker arm surface with a buffing wheel, re-install and monitor.

 

Also verify your spray bar is adequately lubing that area.

[240260280z]

Remove valve cover, pull plugs, then crank with remote starter.

Watch oil flow to rule it out.

If you are getting good oil on that lobe/rocker, then it is most likely the rocker.

This sadly happened to me not so long ago: http://www.classiczcars.com/topic/47101-cam-wear/

Here are some observations:

Contact area is OK and it is "cheated" for more lift.

As the lobe rocks across the rocker surface, it starts parallel (raising valve) but finishes (lowering valve) with more pressure on the firewall side of the rocker. The radiator side seems to be ground lower from the middle of the contact patch to the passenger side of the contact patch and the finishing pattern is not parallel to the starting pattern. This is also evident in the wear on the cam lobe's valve lowering face being more to the firewall side.

Edited April 5, 2015 by Blue

[grannyknot]

So, I charged the battery up and kept the charger on while I cranked, the carb butterflys were wide open and it took 40 sec for any oil to show up coming out of the spraybar. It shot out about 3/4" on some of the spraybar holes and just drips on others. I have a video of it but can't find a way to post it.

 

The spraybar oil holes are consistently 1-1.2mm dia. , 

the spraybar inlet holes are 2.4mm dia. and the cam tower oil outlets is

are 4.8mm dia.

Now I could easily enlarge the spraybar inlet holes to take advantage of the larger cam tower oil holes and that would probably increase the amount of oil spraying on the cam during start up but will I be stealing pressure from some other crucial area?

 

I know the inside of the spraybar is clean as I soaked it in varsol 2,000 miles ago and blew it out backwards with compressed air.

Edited April 11, 2015 by grannyknot

[Zed Head]

Does #5 dribble or squirt?

[240260280z]

There is a restriction in the oil passage at the top of the block that limits oil to the head.

The oil in the head just oils the cam bearings and the rockers. You will just take a little from the cams by enlarging.

I can send you a rocker if you want to replace that one.

[grannyknot]

Does #5 dribble or squirt?

It dribbles, but the oil hole for #5 is the same size as all the rest but it is at the end of the line for that section of spraybar.

There is a restriction in the oil passage at the top of the block that limits oil to the head.

The oil in the head just oils the cam bearings and the rockers. You will just take a little from the cams by enlarging.

I can send you a rocker if you want to replace that one.

It can't take much oil to fill the gap between the cam bearing surface and the cam tower bearing surface so I would be willing to lose a bit of pressure to the bearings to get a little more to the rockers and lobes.

What really worries me is that 40 seconds of semi dry cranking.

 

Can you just trade out one rocker for another? I thought the lobe and rocker had to wear in together.

I'm hoping that by improving the start up oiling that the lobe and rocker won't get any worse or am I just kidding myself?

Thanks,

Chris

[240260280z]

Yeah I measured 45 seconds on my 280z after it sat for the winter in storage.

You can change rockers as long as the surface is smooth, the curve is normal, the alignment of the cam interface is parallel with the lash pad interface AND both are in line. It is best to use Nissan rockers rather than after market ones.

[Zed Head]

It dribbles, but the oil hole for #5 is the same size as all the rest but it is at the end of the line for that section of spraybar.

 

I was drawing the correlation between dribbling and cam wear.  Seems like you might want to balance the hole outputs first, see where you're at, then estimate how extra oil you need to get a small squirt from each hole.  One way to balance flow would be to close up the holes that squirt far to increase bar pressure and drive more oil out of the weak holes.  You could probably peen the edges in with a small drift.

[240260280z]

Flush with canned carb cleaner to improve flow.

Use the straw to spay into holes.

After it is clean, inspect for cracks/ failures of the joints.

[Zed Head]

On the orifices - don't forget the front one that feeds the chain oiler.  Nobody ever talks about that one.  If it got reamed out for some reason, it could unbalance the oil supply,