Pre-Assembly Clearance Check Lessons Learned

[viejopatron]

You may recall that I've been building a 3.0 fitted with domed Ross pistons, Elgin Cam grind 280/270/110 Lobe Centers, Webers and Pre-74 exhaust.

Being a good party member, I will do a pre-assembly to measure clearance between the valves and pistons.

I would like to hear from others who've gone through the process and can relate what to expect, look out for, pay attention to, etc.

My initial reaction was "You gotta be kidding me. Pre-assemble the entire top end to verify a clearance? ", however I agree that changing pistons, cams, etc., etc. and NOT checking might ruin your day.

So please advise with your experiences and Thanks.

[kstylianos]

Lets take a look at those piston domes and see the valve cutouts. Also lift of the cam intake/exhaust will help.

I used JE 9.8:1 CR pistons (large valve cutouts) with very mild Elgin SC330 grind cams. Exhaust and intake valve/piston clearances were almost double minimum.

[asphaltgambler]

Checking costs nothing but some time. parts colliding costs LOTS of time AND $$$$!! An old saying.................."There always seems to be enough time and money to re-do the job second time around"

[cjr1]

Asphalt,
Couldn't agree more! Taking short cuts at that stage of the game would seem risky! Especially with the new cams & pistons. Your comment about 2nd time around hit the nail on the head.Just started my own rebuild & will check ALL clearances,probably twice,even though the only upgrade will be 964 cam grinds courtesy of EBS.This is my first P-car rebuild,so I got plenty time,little dinero!

[asphaltgambler]

I'm an auto tech by trade, currently BMW's. I (as almost everyone in the business) am compensated via production commision. There is always the delema of faster (more$$) vs quality. At some point the lines intersect and then start going opposite directions.

You would be suprised in an engine build how little time it actually takes to measure and check to make certain in light of the time involved for the whole engine build.

And yes, I've learned the hard way, again and again.

[ChrisBennet]

I pretty much check everything that I can including CC'ing to find out what the true compression is. As Aspaltgambler alluded to, it's time well spent.

It's not so much "experience" as it is "accumulated remorse" that influences how thorough you are about checking things.

-Chris

[cjr1]

To Chris &/or Asphalt,
I have another thread(a couple actually)on this board about my rebuild I just started & was wondering your take on rod reconditioning?If they spec out good,should you recond. them anyway or clean them up & install?Thread name is "WOW Look @ all those pieces".There are some pic's of the teardown if interested.Also,do you plastigage the rods?

Thanks

[tom1394racing]

You and I are doing the 3.0 liter rebuild at the same time (check my post on deck ht, compression and shim thickness). I've been wrestling with many of the same question you've asked. I have just completed the deck ht and compression checks and will be starting the top end build-up and valve clearance checks this week.

How far along are you?

[cjr1]

Just did the teardown last week.Still in process of checking out crank,rods,etc.......

This could take awhile.......

[tom1394racing]

You should have your case checked for line bore, cleaned and have the piston squirter's checked and flowed (standard stuff). You should also have your crank magnifuxed for cracks, and either micro-polished or ground under depending on how the journals check out. The main and rod journals need to be checked with a precision micrometer. You should have your rods magnifluxed and have the big ends checked and have them balanced and have the small ends re-bushed. All of this needs to be done by someone who has lots of experience with Porsche engine rebuilding and machining.

When all this stuff comes back from your machining source, you need to spend 1/2 day cleaning everything.

Wayne's book is an incredible resource for all of this information. If you don't have a copy,....buy one.