Amazing what you find when you rebuild

lcolvin · Post by **lcolvin** » Fri Sep 01, 2006 2:08 pm

Hi everyone

Tearing down my engine for a rebuild and have found the following in my 72 991T, thought it was a bit throaty.

Late 7R block, 2.7 heads and 911s conn rods, not sure what the crank is yet - don't realy want to break the case open. I am running Webbers which I am going to send off to get rebuilt in the near future.

Has any one any suggestions on improving the ignition

cheers
Lee

Mick Cliff · Post by **Mick Cliff** » Fri Sep 01, 2006 4:14 pm

"Contact-less" ignition from BS Motorsport (Neil Bainbridge) has been recommended to me by other users on here.

I have the 'box' on order and await delivery...

lcolvin · Post by **lcolvin** » Fri Sep 01, 2006 4:31 pm

Mock thanks for that I will definetly have a look, keep me updated when your new ignition arrives

cheers

davidppp · Post by **davidppp** » Fri Sep 01, 2006 6:05 pm

Hello Lee..

Why not strip the case fully?

I would never recommend leaving this part unchanged unless I had personally done it myself recently..

Its less than 20% of the overall labour in doing even a stock rebuild..and far less with what appears to be a rather hot-rodded motor!

You must make sure it has the oil bypass mod and make very sure you use the big pump for the rebuild, also clear out all the squirters.which are often blocked..

Kind regards
david

lcolvin · Post by **lcolvin** » Fri Sep 01, 2006 6:25 pm

Sorry to sound dumb, do you know were I can get details for the oil bypass mod

cheers

Lightweight_911 · Post by **Lightweight_911** » Fri Sep 01, 2006 6:34 pm

What are the engine serial/type numbers - stamped into the vertical/horizontal surfaces of the crankcase to the right hand side of the fan housing ?

Depending on which year your 7R crankcases originate from, they may already incorporate the Factory oil bypass modification ('76-on).

davidppp · Post by **davidppp** » Fri Sep 01, 2006 6:37 pm

Not dumb at all!

Right, stop right there!

The 911 is much differnet from any other engine I ever worked on in many ways..the two utterly essential books you need are bruce Anderson's 911 performance handbook, and Wayne Dempsey from Pelican's how to rebuild and modify porsche 911 engines.

Bothe readily and cheapy available from Amazon etc..

The Factory manulas are also very useful and well written and illustrated.

There is more than 40 hours work for an expert in a stock rebuild..and just the very basic parts needed cost about 600 pounds even without any actually worn bits!
.you can expect to take maybe double that if you take due care doing it for the first time..

So not to be undertaken lightly..or with the intention of compromising on any slightly worn parts..

You'll get plenty help here, or on Pelican too..

What was the fault originally?

Kind regards
David

lcolvin · Post by **lcolvin** » Fri Sep 01, 2006 7:05 pm

All started with replacing the heat exchangers, you guessed it sheered stud - flat with the head.

Had to remove the head so that I could spark erode the stud out and helicoil.

when removing the headstuds to replace a timesert came out, so had to replace time sert.

Remembering I was burning oil on #6 (opposite bank to sheered stud)

I have now totally stripped the top end and checking all parts and going fit new rings tomorrow

It has taken a little more than 60 hours though

davidppp · Post by **davidppp** » Fri Sep 01, 2006 7:14 pm

Hello, Lee.

Sounds like a US-origin engine, right?

Typically these have got very very hot..is it the dreaded thermal reacotor type..are there injector holes in the exhaust ports?

If so, expect the top ring grooves to be out of spec ( they always are in these in my limited experince) , and many more head studs to be ready to fall out..

As Andy correctly says, the later 2.7's had thwe basic oil system mods..

Kind regards
david

lcolvin · Post by **lcolvin** » Fri Sep 01, 2006 7:28 pm

It is a 73 us 2.4T block with 2.7 mahle heads, have checked the engine number to confirm.

I have replaced all the head studs on the exhaust side also, they were all quite loose though, all are in timeserts obviously when the heads were fitted.

still none the wiser with the oil bypass mod, will buy the books mentioned

regards

Lee

Lightweight_911 · Post by **Lightweight_911** » Fri Sep 01, 2006 7:29 pm

Pulled timesert, oil burning, worn-out carbs...

Sounds like false economy not to strip it right down & do a proper job now you've come this far.

lcolvin · Post by **lcolvin** » Fri Sep 01, 2006 7:39 pm

Thanks for the advise

convinced will split the case, does this need machining bfore resealing. Have read article stating yes and some no?

davidppp · Post by **davidppp** » Fri Sep 01, 2006 10:17 pm

Hello, lee.

I usually try reassembly with just the crank:

Many times the crank spins perfectly..if its even slightly tight, it needs plenty of work.
And, for a road engine, the cheapest option is another case every time.

The problem is not only the binding, but the loss of oil pressure when it gets hot and oil spurts out of the mains..

It will definitely have the early oil system and pump if not modded..

Kind regards
David