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Cam Bearing Caps And Scoring

Cubes

By Cubes,
in Engines & Forced Induction

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Cubes Grand Master

Cubes

Posted
Posted

Hey ppls,

I've recently pulled the cams out to find there's a little scoring and some polishing on 2 of the cam caps. All pretty much have ever so slight scoring but only 2 have what is noticeable so to speak and one looks a tad concerning.

Is this normal? I've pulled the caps off an rb20det I have here and it has the same but not as bad as the one that is a tad concerning.

The tunnel is perfect absolutely no scoring what so ever. its only on the caps.

Is it worth attempting to try and polish/linish out the slight marks or just slap it back together with the new cams?

One last thing to mention is on the surface of some of the cam caps i can see what looks like a black mole... doesn't look burnt just ever so slightly black; much like what a light black skin spot looks like with its faded edges.

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Cubes Grand Master

Cubes

Posted
  • Author
Posted

Nizmonut... You can't buy replacement journals for these I am led to believe.

GTR1993.

There's no oil supply issue that I know of.

I pulled the caps off quite some time ago and there were still a few light lines inside the caps all though they almost looked like machining lines; to touch they can't be felt.

The only difference to now is 1 of the caps mainly has got a tad worse which is concerning and it just happens to be cap 6. Even though the mark is visible it can't be felt.

I am however running a single 1.5mm oil restrictor and blocked rear as recommended by SK.

There's no hydraulic lifter tick and plenty of oil floating around. Oil pressure is spot on and doesn't bleed off on idle.

I've found a few other pics of caps that also appear to have the same strange circular lines inside the caps.

Its also interesting that the lines are ONLY on the cap not the actual tunnel/lower half; the tunnel/lower half looks spot on. BUT I would expect it to as there is next to no load placed upon on it.

Possibly time to take them down for a check up at the local workshop to see what can be done.

CEF11E Veteran

CEF11E

Posted
Posted

Hi Cubes,

what you are looking at it due to 2 things.

1. the caps have been tightened by the looks of it down to 50nm. and due to the fact they are alloy the upper bridges compress to form an elipse causing scoring on the top of the profile.

2. the head may have been suffering from oil starvation due to lack of pressure.

there is really only the option of getting the arcs machined/honed and decking the contact surface so the still form a good base circle, or getting other caps from a decent head and torquing them down to 26nm IIRC?

there is also the possibility of foreign particles in the oil. were these pulled from a running engine?

cheers :P

Rezlo Community Regular

Rezlo

Posted
Posted

Only problem is that even if you could get new ones each one of those journal caps is unique in mount offset, easy way to see is to swap some of those caps around and youll see presto hole is now off set by up to 1mm on some motors, Nissan obviously bolts them all up and line bores so that even if there is slight variance in the cap mount the hole is still perfect. So if you need to replace any you will need to line bore it. Easy way to do it is to have .5mm taken off the caps, bolt them all up and have it line bored, its only the caps that score not the head due to valve spring load.

The guys here in South Africa always use oil filters that dont have anti drain back valves which causes gauling and damage to the cam caps especialy in SR20's, takes up to 10 seconds from start up for the oil to start coming out the spray bars with no drain back valve in the filter.

It cost about the same here to have both sides line bored as it does to bore and hone the same size motors cylinders, cant imagine it being that much more in Ausi

Cubes Grand Master

Cubes

Posted
  • Author
Posted

Cheers Shanef and thanks all.

Gulp/Swallow.... Here's the pic of the exhaust cap 7 to 2 from left to right respectively.

Closer inspection. The black marks on cap 7 is actually corrosion. :S

I do remember it being there ~80,000km's ago when the motor first went in; it doesn't appear to look any worse from 'memory' but it was a long time ago.

The camera has shown up fine scratches that i can't actually see by eye unless i get really really close and shine it on certain angles in the light.

You can see the polishing on the lower (pic) side of the cap.

If it has to be line bored it has to be done. :laugh:

post-382-1213793603_thumb.jpg

roba Enthusiast

roba

Posted
Posted
what you are looking at it due to 2 things.

1. the caps have been tightened by the looks of it down to 50nm. and due to the fact they are alloy the upper bridges compress to form an elipse causing scoring on the top of the profile.

What is the correct tightening torque???

Cubes Grand Master

Cubes

Posted
  • Author
Posted
cubes, on second look they dont look to bad at all.

if you run your nail over the scratched can you feel them? or does it feel pretty smooth? they looked worse in the first picture

That first pic was some other motor that I found via google.

Yeah they aren't too bad but yeah the corrosion + I really am not sure if they should have absolutely no scoring or a little is fine.

Running my nail over it its not perfectly smooth but the nail definitely doesn't catch on it so to speak.

Rezlo.. Thanks for the pics buddy. The RB's have the anti drainback located in the block. I'll head down before work starts and have them checked out juuuuustt incase.

Wouldn't want to scatter alloy fillings through out the motor. :S

Some more pics that I took in daylight.

The inlet is definitely in better nick than the exhaust but one still has corrosion/cancer.

Couldn't get down to have them checked out today. Will have to be next monday now. :)

post-382-1213840301_thumb.jpg

post-382-1213840312_thumb.jpg

Rezlo Community Regular

Rezlo

Posted
Posted (edited)

Yeah I know the RB does, just an example of the repair.

Honestly yours dont look that bad, that spot or corosion is tiny, I would say dont bother unless your running some hard core cams and springs which would load them a lot more than stock.

Edited by Rezlo
Rezlo Community Regular

Rezlo

Posted
Posted
does anyone have a spare set of caps? i need a set (or 2- to try and match up as close as i can, then to line bore out.)

pm me if anyones got any

thanks

Why dont you just have them taken down .5mm or 1mm and reuse them? even if you find the near perfect cap and its got a TINY TINY offset and you line bore it would mean that only 50% of the new cap will get machined, and it will be on they higher side of the stock specs, if you machine yours down and reuse you can get pretty much the exact factory clearance + cost savings.

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