Case assembly question

Bob Goding · 04-30-2004, 06:05 PM

Machining the case-halves recently, I noticed something
which I have not seen discussed previously.
When facing the case thru-bolt surfaces [7R,magnesium] I see that the
right side case-half holes are chamfered or countersunk, presumably to accomodate some of the o-ring,as the spigot on the thrubolt would fit the hole snugly.and the o-ring can only go into the washer. On the other side case-half, the holes are not chamfered and as the bolt diameter is smaller than the hole the o-ring would crush into the hole a bit and probably act as a center locator. Several of my hole surfaces appear to have been 'off center' on the nut side. thus requiring the resurfacing.
On page 134 of the bible[How to rebuild & modify] Wayne suggests that it would not make much difference which way the thrubolts went in ,but it looks to me that it might be important to do them as directed.
I do recall reading somewhere about the o-rings 'squishing' out from under the nut when torqued and I think that the article
suggested an updated blue o-ring,but I cant recall where I saw that.
I would like to see a flanged locater sleeve,to center the nut end of the stud and accomodate the o-ring same as the bolt head end.
Not sure that we faced enough material from the case to accomodate such an item ,but I might make some and see how it looks .
There must have been thousands of these things assembled over the years,what comments might we have ?
Thanks--Bob

Bob Goding · 05-01-2004, 10:36 PM

Well,team! usually when I write something that I think I know about, I get flamed right off the forum, so since this one didnt
raise a response, I moved on to stage two---design the insert.
But I hadn't taken in to account the thread diameter at the nut end!
Measuring the thru-bolt length, from under the washer at the head end to the end of the 8mm wasted shank,or the start of the 10mm thread,I got 212mm .
Then measuring the two case halves[after machining] resulted in
a figure of 215mm.
This will leave a thread or two to locate that end of the bolt,and the nut end washer ---but the o,ring,will be squashed into the thread.
No wonder the knowledgeable advise RTV to help seal these things.
Just didnt seem right somehow.
Bob

one 76 2.7
two 2.7 engines!

Wayne 962 · Wayne 962's Garage

Hmm, now you've got me thinking. I've read your post about 5 times, and I think I understand what you're asking. In the book, my engine case only had one side spot-faced because that's all it needed. I know that on this spot-face, the holes were not chamfered. I have an aluminum case (and another mag case right downstairs in my garage - I'll go check them in a minute).

-Wayne

Bob Goding · 05-07-2004, 06:42 PM

Wayne, did you conclude anything ? [or are you still down there?

Bob Goding · 05-10-2004, 11:32 PM

Well, it looks like this has gone to the 'too hard basket'--------
I still feel that it looks wrong,tho!
So, after a long period of procrastination, I finally got around
to putting in the dreaded 'Timeserts"--as I had reached a dead end ,trying to purchase the 'case savers' as recommended, and I had the Timeserts anyway.
Inspired by the resurrected 'Timeserts are no good' post ,last week, I took a deep breath and went at it. I used Loctite 222
threadlocker on the outside threads and engine oil on the insertion thread rolling tap.
I must say that I was pleasantly surprised,by how well they went,
the whole 24 were exactly the same to install, and the studs screw in and out by hand. Also, my big worry, the cylinders---
fit into the case with no interference at all, so I assume that there was little or no pushout into the spigots.
Now to put the whole thing together and see what happens.
Bob
77 7R
[ps. with current petrol prices ,it might become a garage queen anyway]

Fishcop · Fishcop's Garage

What spec engine are you building Bob?

Wayne 962 · Wayne 962's Garage

Hmm, yup, got lost in my garage, I'll have to check again soon...

-Wayne

Bob Goding · 06:41 PM

John, it will be a stock spec 2.7--plus------------
SSI, which I have.
New 8.5CSI P&C nikasil,which I have----.As a geriatric teenager,I
need midrange rather than topend,and these 76's have the really long diff,so peaky is useless for me.

At this stage its driven[or parked!] by finance ,but I have some
stainless stuff towards a Triad style muffler. and a bunch of stuff towards
a tbitz EFI.
The engine in the car goes alright,apart from the usual oil leaks
and if I live long enough,I might get around to doing something with that someday.
Bob

76 2.7s
76 Audi 5 coupeGT

Fishcop · Fishcop's Garage

Nice, sounds similar to my build except for RS P&C and S cam and Weber.... Maybe not so similar

It'll be fun to see how the sporto goes behind it!

Wayne 962 · Wayne 962's Garage

I have conferred with others. We don't know. The mag case I have in my garage does not have chamfers. The 3.0 Euro Carrera case also in my garage has the chamfers on one side, but not the other. I had some other people check too. Some cases only have them on one side, some have none, and some have them on both sides.

Perhaps the chamfers have been added by machine shops throughout the years? Walt at Competition engineering did not put any chamfers on the through-bolts on my mag case used in the book. I would defer to him for the definitive answer on this issue...

The use of the black silicone sealant really eliminates any insecurities on this issue though...

-Wayne