AO

Keep asking questions y'all. I don't feel it's hijacking as I'm still taking things apart.

I got my plastigauge set today. $11.99 from JEGS and because they are about 2 hours south, I got it overnight. Cool! I'll be measuring clearances this weekend, Clarence. Roger roger roger... I guess I picked the wrong time to stop sniffing glue? Hey! What can you make of this? I can make a broach, a pirate hat, or a pterodactyl...

Tonight I started cleaning up the valves. I haven't measured the guides yet. That will probably happen after I get them cleaned up and I can sit for a couple hours.

Basically, they way I was taught to clean up valves is to chuck them in a drill and then take them to a brass wire wheel. Cleans them up lickety split. I only got a few done before my drill ran out of juice.

So, for ***** and grins I decided to see how well they might lap into the head. To my surprise, They look really good! I am by no means an expert at this stuff, but there si a nice unifor gray circle all around the seat and the valve. Tomorrow night, if I work on it, will be to finish the rest of the valves and start checking the guides.

All the valves in a box... (See Dave! )


One before (right) and one after (left) cleaning.


Again, before on the left, after on the right. These are intake valves.


Here are some exhaust valves. Before on the right, after on the left. Minor pitting/staining on the left.


So I tried lapping in one of each valve. Here you can see the exhaust seat on the right has a nice uniform gray band from the lapping procedure. If your valve is bent, it won't be uniform.


Here is the corresponding exhaust valve. It's the same one from the pic that showed the minor pitting/staining. Looks good to go to me... sorry the pic is slightly our of focus.


Then I decided to do the intake valve. Here I show the gray band on the valve and the seat. Looks good to me.


In this final pic, I show a clean valve on the left that has NOT been lapped. The one on the right has been lapped. Notice the nice band of gray.

daveo90s4

Good boy!!

The seats that you've done don't quite look there yet, but are a significant improvement. Can you get hold of a valve lapping tool like the one I mentioned, rather than using the fire stick method. From my experience, using the fire stick method means you get real sick of it real fast, and may not be inclined to give it that extra bit that is needed. Good progress.

AO

As I mentioned, my drill crapped out. I was going to try the drill method Rod prescribed... but decided to give it a whirl by hand since it was "right there". I only did these two to see if it was worth it or not. Looks like it might be. Before I do them all, I need to check the guides. That comes after I finish the cleaning.

the flyin' scotsman

what type of grinding paste are you using Andrew?

Fire stick method typically has a coarse and fine followed by 'blue' to check the seat widths.

AO

Permatex something or other. Just had the one type at the store. Will see if I can source a better "Set"

GregBBRD

Yes. No.

Completely dependent on how the bearings measure and how your crank measures. A couple of years ago, every Glyco bearing I could find was a very "tight" bearing and I was forced to buy all my bearings from Porsche (expensive), in order to get the bearing clearances I desired.

More recently, the Glycos I've measured are much "thinner" and seem to be a better fit, for crankshafts that are in the "middle" size category.

On very high tolerance crankshafts (larger journals sizes, within the specifications) special attention must be taken and hand selection of bearings may be required....especially for the cylinders that seem to respond better to higher bearing clearances. In these situations, it is common for me to buy factory rod bearings sets, take out the red bearings from each set, and use these.

By doing this, you may end up with an entire inventory of blue bearings (from the sets). Although costly, much cheaper than a failed engine.

For someone who builds engines on a frequent basis, this inventory of "blue" bearings isn't usually a problem. It will only be a matter of time until your will run into a crankshaft that needs tighter bearings.

It's a bit harder for the "home" guy to rationalize having several hundred dollars of bearing inventory, so generally compromises are taken or different approaches are used.

The reality?

This stuff has to be measured very carefully. Plastigauge is virtually useless. If you can't physically measure the bearings, the rods, and the crankshaft within .00025"....take the pieces to a machinist that can. If you have a machinist that can't read to these specifications....you need a different machinist.

GregBBRD

If you pay any attention to the valve guide clearance wear limits that Porsche quotes, the valves will damn near be able to both run in the same valve guide before they need to be replaced....the specification is silly.

These are absolute wear limits.....not rebuilding limits.

It is rare for an engine with over 80,000 miles to not need exhaust guides. Intake guides are frequently still good past 150,000 miles.

I see no reason for your engine to not be the same as the majority of the other engines.



I'd love to see some close-up pictures of your head gaskets.....especially the fire rings. There's more to be learned there than anywhere else, on the top of the engine.

Rob Edwards

Made me look at my inventory. This is my stash for whatever motor needs them next. 10 sets, 20 halves, all stamped 09/04, bought in October 2010.

All 20 are yellow. You'd have to buy an awful lot of bearing shells to get a set of 16 reds or blues....

69gaugeman

Andrew,

If the valve is bent, the seat will still show the grey band all the way around. The valve will not. Of course it also depends if the valve is bent less than the valve guide wear.

69gaugeman

For the most part I would agree with this. When you change something (grind the crank or resize the rod) you cannot beat measuring the journal. Mostly because size is not black and white. The geometry (taper, out of round, etc) is as or sometimes more critical in the running of the engine. Or course crank angle and stroke should be measured too, but most people don't have 200k to buy a used crank angle gauge.

The factory specifies the use of plastigauge for clearance ,and on an engine that ran fine before and showed no signs of journal wear, it will be fine to use.

AO

Sorry, I wasn't clear there. Thanks for clarifying.

GregBBRD

As we found out before, you are the expert.

I'm just a guy that works on 928's 300 days out of the year and builds hundreds of engines.

BC

Thanks Greg. It makes me want to look at what F1 does. Of course they heat their water and oil before start up. And a million other things we don't even see.

BC

Yes Rob, I have not seen much multi-colored sets from Porsche the last three times I bought (2009, 2010 and I think 2012.

69gaugeman

There is no doubt in my mind you are the finest 928 master mechanic out there. And I am being serious. I do not for a second question your ability to build a 928 engine.