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One way to verify that the cam journals are still true is with plastigage.
I have plastigauge. They are .025 to .076 mm and .051 to .152 mm clearance ranges. From what I have on the instructions and what I've seen in youtube videos I place the plastigage perpendicular to the cam cap, tighten to torque specs, remove the cap and measure the width of the crushed plastigage with the ruler on the plastigauge envelope.
Which plastigauge version should I use?
Anybody know the clearance spec for the cam journals?
I even spoke to the machinist that did all that and the welding. Each machinist has there own metal stamp they use to indicate the heads they worked in.
In my mind very professionally run. I asked about bead blasting and they said it was one of their steps in the process that includes a thorough cleaning of the heads. I also asked if they have ever had any returns due to beads material left behind and they said no. I trust them.
Do some search here on oil galley and media blasting of heads. You should remove the caps and clean them out.
Putting the hard on a glass and rocking it does absolutely nothing. If you want to measure the heads, either take it to someone that knows how to do this or get someone to show you how to do it. I would never blindly trust anyone unless I can actually check their work.
I even spoke to the machinist that did all that and the welding. Each machinist has there own metal stamp they use to indicate the heads they worked in.
In my mind very professionally run. I asked about bead blasting and they said it was one of their steps in the process that includes a thorough cleaning of the heads. I also asked if they have ever had any returns due to beads material left behind and they said no. I trust them.
If you didn't remove the oil pressure check valves before sending the heads, removing them now will give you a quick visual of the trapped beads in the oil galleys.
Regardless, study the oil galley drilling in the heads, carefully. There are a bunch of drillings that end in a dead end, past the intersecting drilling.
Impossible to blow the oil and stuck beads out of a dead end....you can soak and blow for a week and not get it all out. The plugs must be pulled, the oil galleys cleaned, and new plugs installed, if the heads got near a bead blasting cabinet.
If you are lucky, there's just a tiny amount, but even a very tiny amount will ruin an engine.
Like I said, instead of being pissed that I might know a bit more than either you or your machinist, just say: "Wow, thanks for the heads up."
If you didn't remove the oil pressure check valves before sending the heads, removing them now will give you a quick visual of the trapped beads in the oil galleys.
Regardless, study the oil galley drilling in the heads, carefully. There are a bunch of drillings that end in a dead end, past the intersecting drilling.
Impossible to blow the oil and stuck beads out of a dead end....you can soak and blow for a week and not get it all out. The plugs must be pulled, the oil galleys cleaned, and new plugs installed, if the heads got near a bead blasting cabinet.
If you are lucky, there's just a tiny amount, but even a very tiny amount will ruin an engine.
I agree about the oil pressure check valves. I have the o-rings for replacement. I can do that now.
No sign of glass beads. But there were fine bits of metal attached to the ball. Took a q-tip to the intersecting galley. No busted glass.
I have plastigauge. They are .025 to .076 mm and .051 to .152 mm clearance ranges. From what I have on the instructions and what I've seen in youtube videos I place the plastigage perpendicular to the cam cap, tighten to torque specs, remove the cap and measure the width of the crushed plastigage with the ruler on the plastigauge envelope.
Which plastigauge version should I use?
Anybody know the clearance spec for the cam journals?
Thanks.
I would use the larger- you are not looking for an absolute measurement, rather variation among the journals. As they must have been line bored originally, I would be suspicious of anything much greater than a tenth. I would do the PG twice at 90 degree separation of location on the journals. Of course, mike the cams too, as you want to eliminate that source of variation.
Hopefully those more experienced than I will correct any misdirections I may have given here.
I think the spring needs to be replaced. The o-ring is half gone and the reset turned to dust.
These Heads are from a 187ik engine.
Kevin, the oil in normal running is filtered long before it gets to those check valves and you will never see metal there. All of that large metal debris came from?
The machine shop.
Take the valve springs and valves out. Pull the end plugs. Re-clean the heads and the oil passages with long brushes. Re-assemble with new oil galley plugs.
I remove the check valves, before sending heads to the machine shop, so the ***** and springs don't get damaged like yours. The machine shop removes and replaces the oil galley plugs on their own.....the replacement plugs are the very last thing to be installed, before the heads are put in the clean bags.
I've "redone" more than a couple of engines because of this very issue....with really sad clients reaching into their wallets the second time, for the same job.
Believe it or not, I'm not just here busting your chops....I'm only trying to help.
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
Are you referring to the big plug (appears to be new) or the two small ones?
All of the small ones.
Go down to Harbor Freight and see if they have a small slide hammer with a screw in point (mine is Snap Off, but I'm guessing HF will have something similar). Drill a hole in each plug and remove them with the slide hammer.
Clean these passages with a long appropriate brush. Be aware that all the oil galleys to the liters are drilled perpendicular to these passages....so there is a lot of passages to clean.
Next set of heads, pull the oil check valve and the plugs before they leave your hands. Allow them to do their work, reminding them to rinse and blow out the oil galleys before they assemble. When the heads come back, you can put in the plugs, a new O-ring on the check valve cap, and be done.
I know it really seems invasive Kevin - but I have done this on several sets of heads myself. Getting those galley's clean is a very educational moment, at least for me.
I drill them and then put a slide hammer over a small bolt and thread the bolt in. like 3 minutes a plug.
Then you just need to make sure you get the right parts for putting the plugs back in.
I'm assuming that Roger carries the replacement plugs? I'm definitely glad this came up before I put mine back together.
Yup. Huge problem with the rebuilding 928 engines/redoing cylinder heads on the late 928 engines.
"The devil is in the details".
Look at Kevin's picture and try to imagine that metal on those check ***** going to the tiny check valves in the lifters or to the aluminum bores for the cam journals in the heads....because that is where it is going to go, in the first few seconds of running.
Instant, complete junk.
The plugs you need are N011918.1.
I do so much of this stuff that I order them 100 at a time. I'd guessing Roger will have them.
The cleaning of the oil gallies should have been the machine shops responsibility. Instead of making the heads look clean on the outside (painting them), they should have spent the time cleaning the inside. Worst part is that until Greg posted, Kevin didn't beleive me and more than likely would have dismissed my post and installed the heads as is.
06-26-2016, 11:38 AM
