blown 87

How much thrust end play does a new thrust bearing normally have?

Mine has .009 on the stand with only the rods connected, I think .012 is the wear limit.
I am afraid I know the answer to this before, but run it or replace it?
I do have a super clamp from Constantine.

Greg Nettles

Nicole

What does it cost to replace it now, and what would it cost to replace it later?

blown 87

About the same, just a bit more time.
My biggest worry getting the clearances right when I replace it, no way to adjust it.
I guess I can get a set of mains and the thrust bearing and see what I have got.

John Veninger

blown 87

So it is .02 from the largest clearance new?
Am I getting that right?

Mrmerlin

what is your measurment in mm thats what the page John V sent is in mm. Since your down this far it would be a good idea to remove the crank send it out for polishing and replace your mains, Clean the crank atleast 3 different times with brake cleaner and carb cleaner with compressed air followed by a hot water and soap wash , spray the crank with WD40 after to prevent rust. There will be lots of polishing compunds inside the crank after polishing

Fogey1

http://www.sks-bottle.com/340c/mmTOinch.html
converts John's figures to:

.06mm = .0023622in
.192mm = .00755904in
.40mm = .015748in

Your measurement:
.009in = .228599999...mm

So, you're .001441in larger than widest new and .006478in smaller than the wear limit. Say 20% of the way to the limit.

I'd say it's your call. But consider Nicole's point - and you're adding big power.

Tails

millimetres to inches multiply by 0.0397.

My TB end play is 0.008" and this is after 18 years with a migrating clamp for the first 16 years and 94,000 kilometres. Forward flexplate clamp is now stationary on TT drive shaft splines with an application of locktite for the last 2 years and clearance is still 0.008", as it has been for over 5 year since I started checking it each year. One can assume that the TB is doing its job and is in alignment with the crankshaft.

If you change the thrust bearing you have to be sure that the thrust collars on the crankshaft are polished, they are flat and are at right angles to the axis of the crankshaft. Special cutter grinders need to do this in competent workshop.

When you fit the new main 'thrust' bearing the thrust wear faces of the main bearing must be flat (this means that the edges of the thrust face of the upper and lower bearing must be flat and in axial and vertical alignment with other), so that they contact fully with the thrust collars on the crankshaft. The thrust bearing faces must also be at right angles to the axis of the crankshaft through the block.

Collar type thrust bearings with metal to white metal bearings are the worst type of thrust bearings used and they are be subseptiable to lubrication brakedown, heat generation and metal to metal contact, if the end load limit is exceeded.

There is an old saying "if it ain't broke don't fix it", so if the thrust bearing axial bump clearance is still within specification limits and is not right at the upper limit, do you really need to change it? That is the question you need to ask yourself.

More damage is done when thing are pulled apart and not put back together correctly. Do you have the capacity, the tools, the competence and a good workshop to preform this task, knowing that originally it was assempbed in Porsche's workshop assembly facility? This task is not beyond the capability of a competence of a DIY person.

Tails 1990 928 S4 Auto

Mrmerlin

Check the wearing surface of the crank/thrust area.
To seat the TB main hit the end of the crank with a wooden block and hammer from the rear before you tighten the girdle this should align both halves also make sure the oil pump is in while the girdle is being tightened

blown 87

It is not broke now, and I know everything fits right, but it does have to come apart to have the block surfaced for prep for the Cometic head gaskets.

I think I am going to have my machinist look at the crank and make a recomendation on what to do.

As far as having the capacity, tools and workshop, I have that covered.
We shall see about the competence part.
Even though I do work on cars for a living and hold a A&P license, building motors is something that we do not do a lot of, maybe one a year.

Over the years I have came to the conclusion that nobody (that I can afford) will take as much time and be as **** about things as I am.
I have paid big money for some big name builders to do motors for me with very little luck.
(not Porsche motors)
I could tell you about it, but it would not do any good or change anything.

I feel confident that with the help I can get here that I can do this.

Abby Normal

I's get that Super-clamp in there pronto!

blown 87

That was one of the first parts I put on the car after the timing belt, I think I put it on before I had a hundred miles on it.

Mrmerlin

if the block is getting cut then you will need to remove the crank anyway and refit the girdle,
too much chance of cutting debris getting into the oil ways and bearing/crank , So i guess this answers your question, Refit the block with fresh bearings and polishe the crank, follow the above instructions about cleaning the crank

blown 87

I knew I was going to take the Girdle and crank off, I was thinking of re-using the old bearings, now that i see how that looks when I write it, it sounds foolish.
What is a good solvent for removing the old sealer from the girdle?

Mrmerlin

Acetone will work also you can use a razor blade perpendicular to the sealing surface to clean the old loctite off make sure to use the correct stuff when you put things back together I think its 574 setting sealant This stuff onlt seals when air is removed so the oil will rinse out the extra. Goodluck on your rebuild. Also pay careful attention to the main bearings as they can sometimes wear funny due to belts being too tight, or Auto drive shafts slipping forward