GregBBRD

I have not had a machinist for over 40 years that uses Plastigauge. They measure everything and actually calculate bearing clearance.

I personally have not used Plastigauge for 40 years. I measure everything and calculate the bearing clearance.

However, your point is well taken, for a running engine with a really nice crankshaft and an original set of matched rods. Platigauge is far better than not worrying about the different bearing sizes and just stuffing a set of any old replacement bearings into the engine.

But it is a little bit like mowing your one acre lawn with a set of hand shears....

By the time someone gets done measuring a whole set of rods with Plastigauge, swapping the bearings around to where you want them, and then repeating the entire Plastigauge exercise, a bearing micrometer is going to seem like the invention of the wheel.

In this imperfect world....I've had more than one "red" rod bearing that actually measured as a blue. I've also got a little box of rod bearings that are such strange sizes....I have no idea what happened. Some are marked "Blue+++" and some are marked "Red----".

I think the entire point is that you can't assume anything. Every piece needs to be measured and compared to what you are replacing it with.

In my opinion....a bearing micrometer, is like a connecting rod bolt stretch gauge.....no one should attempt to rebuild an engine without one.

Measure the true thickness and put the bearings where you want them. If you end up with a boatload of "yellow" bearings, sift through them and stick the ones with the highest clearance into the cylinders that need the extra clearance and put the rest in the other positions. If you end up with a set of Glycos that measure really tight....do something else.

928 at last

In thirty-nine years, (God it's been that long?), I've seen my father in law build many engines, and I've never seen him use anything but a mic for the measurements. Never heard of an engine coming back once he finished it either for that matter.
If I were going to this amount of time and effort to do an overhaul, (and I may one of these days), I'd be using the micrometer. Just not worth rolling the bones on one of these engines.....
My $9.28....

928 at last

Mind you, I've never seen him use a power tool for lapping the valves either.

928 at last

What Malcolm and Dave said.....
Two grades of paste, coarse and fine, and "Engineer's Blue" to check your work.
Takes many hours to do by hand......

the flyin' scotsman

A recap of valve specs:

Imo000

I always only used one paste and have lapped tons of valves over the decades. Never had any issues. The lapping shows where the valve sits so I'm not sure why bluing it is necesarryon a street driven car. Maybe on a race engine. The compund I mostly use is Pematex but have made my own once when I was out of it. Grinding stone dust and grease, worked like. A charm.

the flyin' scotsman

Done a couple of valves in my time also.....coarse followed by fine then blue used to show where/how the valve/seat are mating.......how I was taught a long long time ago, each to there own

SeanR

Happy birthday Andrew.

FredR

For those interested a link here

http://www.carcraft.com/techfaq/116_...lastigage.html

Seems they are in the Dr Brown camp -surprise surprise.

If one is going to take on something like this then not having the correct tools makes zero sense to me- especially on a high end/spec motor. I presume Porsche maintain very high tolerence controls when building their motors so why compromise that?

There again I suppose one could use some emery cloth on the high spots!

Hilton

This thread makes me want to go buy a ball-end micrometer.. and I'm not even planning on doing rod bearings (or taking my engines apart)

AO

Thanks Sean!

Didn't do a whole lot over the weekend. I finished measuring all the valve wobble, and it's pretty damn clear I need to new exhaust guides. Intake guides are still very tight.

In general all the exhaust guides measure in at between 0.50mm and 0.60mm. The intake are all pretty much around 0.25mm.

I have a good shop in mind to do the guides. I presume I need to have the seats re-cut? I may start a new thread to ask and walk through what goes into getting new valve guides. Anyone BTDT? I presume this is not a home or DIY job.

I mic'd the valves and there is no perceptible wear on the stems - so that's good, I guess.

Later this week, I will probably separate the block and inspect the bearings, but I am working on the assumption that all is good there. I also need to dis assemble the SCer and see where the leak is on the intercooler and get that fixed.

Sorry no pics today...

69gaugeman

Not really a DIY job as the seating tool is pretty much a specialty item. And yes, you must re-cut the seats after a valve guide replacement.

You might be able to save some time for your re-builder by removing the exhaust guides, but it may not make a difference to your vendor. Ask them to see.

ptuomov

I don't know what I am talking about but here are some thoughts.

I think the valve seats need to be recut because the seat cutter indexes of the valve guide. If the new guide bore is not aligned exactly like the old one, then the valve doesn't seal without recutting the seat.

Even when recutting the seats, logic dictates that one wants to get the new guides as closely aligned with the old guides as possible. I think this minimizes the chance that valves end up too deep and the seats have to be changed.

I have heard that some people first thread a bolt to the seal side of the guide, as shallow as will fit. Then, they drill out most of the valve guide from the port side until the drill tip touches the bolt. This will remove most of the interference fit and the guides can be pushed out with least amount of force, creating the least amount of distortion to the aluminum bore. The same people cool the new valve guide with dry ice (why wouldn't my wife's freezer do?) and barbecue the head to 250F so the new guides can be set with the minimum force. Allegedly, this way the new valve guides will be about as closely aligned with the old guides as possible. I am not vouching for this procedure, just noting that this is one story.

I've got a digital mike that has a ball anvil in one end. It's supposedly very accurate. In practice, since it's a hand held mike and not a laser stand, a human operating the mike can never get to the stated precision. When measuring bearing shells, I am getting 0.002mm (0.00008") measurement error standard deviations for bearing shells and 0.003mm (0.00012") measurement error standard deviations for Honda-size rod journal (with a similar two-flat anvil mike.) These are measurement errors for measurements taken in temperature controlled environment within a 20 minute period, so measuring say on different days in slightly different temperatures would probably give much bigger measurement error standard deviations.

Any thoughts about whether what I said about the guides makes sense?

the flyin' scotsman

Happy bday AO........hope your tilting a few today

The measured valve guide play while perhaps not tight is within spec......your engine, car, $$$ but for what may be gained I personally may lap all valves, replace the guide seals with new then concentrate elsewhere.

Be interesting what the pros recommend.

123quattro

Andrew, I would recommend Thompson Automotive in Wixom.

http://www.thomsonautomotive.com/contact.html

They did my Euro heads and all the head and block work on my Audi 200 20v. They also build all the engines for the GM SEMA cars.