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'73 modified E rebuild

Posted: Mon Feb 15, 2016 6:13 pm
by Tony
I'm a bit reluctant to post this given all the truly excellent restorations on here and the number of E's that seem to be 'in progress', however somebody might find it useful so here goes.
I've been the happy owner of a modified 911E since 2012, engine believed to be to S spec with hi comp pistons and a Bob Watson rolling road sheet (196bhp).
This rebuild was initiated by serious knocking noises from the engine in the middle of 2015. My immediate reaction was that I'd run a bigend, I had a huge amount of history which indicate that although the top end had been rebuilt to S spec 20000 miles ago the bottom end was untouched. A bit more digging found a in invoice for replacing main and big end bearings but over a hundred thousand miles ago. So a big end seemed a reasonable deduction.

The car sat around for a month or so, I knew it meant taking the whole thing apart and was reluctant to bite the bullet!
Then friends at Gantspeed offered me a corner of the workshop to strip the engine and provide guidance, taking over the rebuild when necessary.
So offer accepted and off we go.
Stripping the engine down a number of things became apparent, Crank and bearings were good so not a big end then. It did look as if at some point the cams/rockers had been starved of oil so there was obviously a problem somewhere. There was wear and tear in the valve gear and oil leaked from all over! Cleaning and measuring gave us an initial list of problems:

The timing chains and idler gear were worn out
The intermediate gear was worn and had suffered some surface damage.
The on-engine oil cooler leaked
Both cams were pitted and worn as were several of the rocker arms
Several rocker shafts were worn
The valve guides were worn
The little end bushes were worn and needed replacement
The valves and springs were sufficiently worn to need replacement

Some of the effected cams
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Old and new sprockets for comparison
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Re: '73 modified E rebuild

Posted: Mon Feb 15, 2016 6:52 pm
by Gary71
Excellent. Another engine rebuild:) Always good to see them as I always learn something new each time.

Re: '73 modified E rebuild

Posted: Mon Feb 15, 2016 6:59 pm
by AndrewSlater
What Gary said - can't beat an engine rebuild thread. :wink:

Re: '73 modified E rebuild

Posted: Mon Feb 15, 2016 7:08 pm
by 210bhp
Hi Tony

You are at a good place at Gantspeed. Nice gentlemans agreement they made with you.
Im sure you will be fitting new under the expert guidance of the team there but FYI I do have,

Timing chains
Idler gear (I think)
Intermediate gear
Engine oil cooler
Chain ramps
Full gasket set
Chain tensioners
Cranckshaft
Rockers
Engine tin
Pistons (new)
Oil return tubes
Etc

I was going to advertise these on Ddk soon but if there's anything you need give me a pm.

Good luck with the build and keep the updates coming.


Regards
Mike

Re: '73 modified E rebuild

Posted: Tue Feb 16, 2016 4:36 pm
by Tony
Ok, Google seemed to have screwed up Picassa so I need to find another hosting site - until then no pictures - but more words!
On the positive side:
The crankcase halfs were in excellent shape
The main and big end bearing shells though worn were still in tolerance
The crank was in excellent condition
The engine had been bored to give a capacity of 2399cc
All pistons and rings were in good condition, pistons were JE of uncertain compression – but each cylinder had 4 base gaskets (to be investigated later).

However none of the above was an obvious cause of the sort of knocking noise that started all this!

I had a comprehensive history of work done on the engine and knew that in 2005 work had been done which create a high compression S engine running on Webcam 120/104 cams and fitted with Ssi's.. I'd had the injection checked and everything reset and had fitted a 123Tune programmable distributor.
All this meant that I had the bones of a very good engine – albeit one requiring some pretty serious component replacement.

As I said earlier the stripdown and measurement I did under the watchful eye of Gantspeed Engineering, Although I'd previously rebuilt a 3.2 that was largely from a nice clean kit of parts. Even aided by parts washer and media blasting it took me over a weeks effort to get to the point of a clean set of parts that could be measured and inspected.

Once the condition of everything was assessed the heads went off for new guides to be fitted, rods went to have new little end bearings installed, all the tinwear was sent out for powder coating.
A large shopping list was assembled:
Oil cooler
Main bearings
Big end bearings
Little end bearings
New rod bolts and nuts
S cams and std rocker arms, rocker shafts
Valves and Valve springs
New intermediate shaft
Intermediate shaft bearings
New timing chains
All new idler gears
SC Oil pump (actually the old one was fine but 'while everything's apart' this was to be fitted in conjunction with the oilway mod)
Appropriate Oil pump 'strainer cover'
Pressure relief valves
New barrel studs
Flywheel bolts
Clutch
Complete gasket set
All new fasteners and washers

There were now a number of 'pre build' jobs to be done.
On the crankcases the oilway mod was done, the barrel studs were replaced – without time certs (a number of reasons for this, basically engine size, crankcase condition)
The oil way plugs were removed during cleaning – after further cleaning these were replaced.

The crank was crack tested and balanced, with the flywheel.
So just get all the bits delivered and it could go back together!

Re: '73 modified E rebuild

Posted: Tue Feb 16, 2016 5:29 pm
by 911hillclimber
Chain guides and tensioners?

Re: '73 modified E rebuild

Posted: Tue Feb 16, 2016 7:17 pm
by Tony
Ah yes, new guides but tensioners were fairly recent and fine just that all the sprockets were trash.

Tony

Re: '73 modified E rebuild

Posted: Thu Feb 18, 2016 12:45 am
by Tony
The rods were returned and were balanced

The heads once returned, were refaced and the valve seats re-cut, however the replacement of valve guides may have answered the knocking question as the machine shop were able to push one of the guides out by hand!

So after a not inconsiderable time (waiting for parts and sub-contracted work) The rebuild began.
First step was to assemble the rods onto the crank with new, lightly oiled nuts and bolts, then fit the end seals.
Then insert the intermediate shaft bearings, fit the oil pump, Intermediate gear, timiming chains to the lefthand crankcase.
Insert Bearing shells and apply sealant to the crankcase. Install the crank and with the rods and chains held out the way put the two halves of the crankcase together.

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Tighten all the peripheral nuts round the crankcase, check the crank turns – everything ok.
Fit the through bolts with new o rings, tighten, check the crank still turns – Oh Bugger!!!!!! nearly solid.
Further investigation revealed that heating the case to remove the head studs had probably distorted the line of the main journals. The only full proof solution was to shuffle pin and line bore the cases to correct the distortion and then fit oversize bearings. Honing was not recommended as we didn't know either in which plane the distortion lay or the overall severity of it.

And then the next snag! The company who had previously done this work to the desired standard announced that the only engineer who did this work had retired and they didn't have anybody else who could do it!

Re: '73 modified E rebuild

Posted: Thu Feb 18, 2016 7:12 am
by sladey
Oh bugger....

Better to find it out now than when it's all back in the car though

Re: '73 modified E rebuild

Posted: Thu Feb 18, 2016 7:44 am
by Gary71
Not good :(

Re: '73 modified E rebuild

Posted: Thu Feb 18, 2016 10:34 am
by 911hillclimber
Ouch indeed.

I've done 4 x 911 engines and never replaced one barrel stud as they have all been tight and true.
Not sure heating would cause such distortion.

Line boring is a big job so good luck.
Keep us posted.
Us engine types love a rebuild of any nature.

Re: '73 modified E rebuild

Posted: Thu Feb 18, 2016 5:51 pm
by Tony
Ok, after some hunting around the guys at Gantspeed found a specialist motorsport company who could line bore the cases not only that they could do it to an accuracy of 2microns! Don't think the originals were that good!

Meanwhile it seemed worthwhile to assemble the heads. The heads were machine to ensure good mating surfaces and any damaged exhaust studs were replaced. The 36 cam carrier/cam cover studs which had been removed during the cleaning process were reinstalled to the correct depth.

A set of .25mm oversized bearings were available from Porsche, so when after a couple of weeks the line bored crankcases were returned and checked we could try again.

The unknown was whether the crank and intermediate shaft was still parallel and if the intermediate gear backlash was within tolerance. Three dry rebuilds later (intermediate shaft only, crank only, both) and everything checked out. So with all new seals and the appropriate Loctite the bottom end was finally put together.

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Re: '73 modified E rebuild

Posted: Thu Feb 18, 2016 8:12 pm
by sladey
You're playing with our emotions here!

Re: '73 modified E rebuild

Posted: Thu Feb 18, 2016 11:21 pm
by 911hillclimber
I thought this was 'real-time'! :wink:

Re: '73 modified E rebuild

Posted: Thu Feb 18, 2016 11:23 pm
by jtparr
You make it sound so straightforward too...!...having never delved into the world of engine building....
Enjoying this one.....