2.7 CIS Engine rebuild - suggestions please

[AndrewSlater]

Apologies to Gary for stealing his title ( imitation is the sincerest form of flattery ) we are clearly at a similar stage of our engine rebuilds.

As part of the restoration of my 1974 impact bumper 911 I am rebuilding my 2.7 CIS engine.
The main restoration thread is here viewtopic.php?f=28&t=51455

I thought it best to run a separate a thread on suggestions for the engine rebuild.

Firstly some scant facts:
The car was non-running when I got it
is believed to have done 85k miles from new
and believed to be last on the road in the late 80's.
It is a standard 911 ( non S ) fitted with the 2.7 CIS engine.
Being a '74 year car the good news is that the engine has a 11 blade fan and no thermal reactors fitted.
The downside being the lack of an external oil cooler.

The engine is just about fully stripped but I have yet to get to the stage where I have measured everything.
First indications suggest that it is a very honest engine that appears mainly untouched, the case seems solid with no pulled head studs. There is evidence of some sort of top end work, as the chain tensioners have been replaced with static Racing Design ones and the timing chains are of the split chain type. The pistons and barrels all seem good.

I intend to do as much of the work that I can myself but will need a specialist for any machining etc.
I do have a limited budget so this isn't going to be a £15K rebuild. (hopefully not famous last words )

So the current (vague) upgrade plan is as follows.


Reliability Upgrades
____________________
Have case savers fitted to the case [ is this really essential on a magnesium 7R crankcase ]
New standard steel case studs [ I assume it is prudent to change the old rusty ones ]
Oil pump bypass mod / newer Carrera style oil pump / New piston relief valve springs
Modification of baffle plates to '78 spec, with cutouts.

Performance Upgrades [If my budget stretches that far]
______________________________________________________
JE Pistons 261664 10.5:1 compression ratio with new pins and rings
964 profile camshafts [reprofile mine or modify 964 ones?]


New parts / other work
______________________
New main bearing shells
New Big end bearing shells
New small end bearing bushes [ if required ]
New IMS bearing shells
Cylinder heads - cleaned / reworked
Return to mechanical chain tensioners [ I do have the static Race Designs ones if any good ]
New camshaft sprockets [already bought]
New timing chains [already bought]
New inlet valves [already bought]
New exhaust system [TBD]
Flywheel refaced? [Mine looks a bit sorry for itself]
New full clutch [already purchased off a fellow DDKer]

Can anyone suggest any other worthwhile upgrades, or any must do machining processes that I have missed?

I intend to take the engine parts to a specialist for an assessment but I am interested in any comments and suggestions.

The engine has clearly last 85Kmiles but I would like to put it back together so that it lasts another 85K and hopefully with some small improvements to the original performance.

As always any feedback much appreciated.
Andrew

[alastairp]

Andrew,

If retaining/ returning to mechanical chain tensioners, rather than later hydraulic Carrera tensioners, make sure you use the later type idler arms.

For piece of mind, fitting chain saver collars is worthwhile with the mechanical tensioners - at least if they fail, you will know about it without total destruction.

Alastair

[redrobin911]

Very interested in how you get on as I've also got a 74 CIS engine and have read up on the 964 cam upgrade with HC pistons - interested to see what additional torque and bhp it's going to make - will you dyno after the rebuild? Is it worth going to a 2.8L setup if changing the pistons - means new barrels? I'll be keeping a keen eye on this tread to see what advise the engine guru's give.

[bjmullan]

Two points from my Mike Bainbridge rebuild.

1. Mike chucked my baffles in the bin
2. Use the Turbo (930 part number) tensioners and Mike doesn't use the safety collars

[911hillclimber]

Never read about binning the sheet metal baffles, only the mods to improve flow (as per Dempsey and Anderson books) which I have done to 2 x 911 engines in the past, but MB is a Wizzard!

If you keep the stock p&b then add a new set of good rings for the pistons. New rings in the existing bores are a good way to determine wear (measure ring gap)

If DIY assembly (good man if you are) then get the Dempsey book; lots of good advice stock and modified builds.

You have not said anything about the induction system! (cleaned injectors/gaskets etc etc)

For what it is worth, get all your machining done via MB Engineering in the Lakes, personal experience of other 'high-end' places failing miserably lead me there with 100% satisfaction and no rip-offs at all.
Lastly, the full long-block DIY rebuild I did on my 3.2 cost about £1000 in bits from Type911 iirc ( no tensioners (hydraulic)) and machining on top (ie valve guides)

Good luck and detail it all on your thread!

[bjmullan]

Never read about binning the sheet metal baffles, only the mods to improve flow (as per Dempsey and Anderson books) which I have done to 2 x 911 engines in the past, but MB is a Wizzard!

At least I think it was the baffles he chucked!

[Lightweight_911]

Two points from my Mike Bainbridge rebuild.

1. Mike chucked my baffles in the bin

I think the confusion is over nomenclature - I would think it's extremely unlikely that MB would advise binning the air deflector plates that fit between the finned cylinders.

However, in the 911 engines I've rebuilt in the past I've always left the mesh screens* out of the crankcase since the edges have a habit of disintegrating & I didn't want those bits circulating in the oil !

My guess is that those are the parts Mike advocates 'chucking' ...

* I think their original purpose was to reduce windage (frothing due to oil aeration)

[bjmullan]

Two points from my Mike Bainbridge rebuild.

1. Mike chucked my baffles in the bin

I think the confusion is over nomenclature - I would think it's extremely unlikely that MB would advise binning the air deflector plates that fit between the finned cylinders.

However, in the 911 engines I've rebuilt in the past I've always left the mesh screens* out of the crankcase since the edges have a habit of disintegrating & I didn't want those bits circulating in the oil !

My guess is that those are the parts Mike advocates 'chucking' ...

* I think their original purpose was to reduce windage (frothing due to oil aeration)

Thank you Andy for the correction, it was the mesh screens that I was getting confused with

[911hillclimber]

Ah!
Makes sense, none in a 3.2 engine so maybe that's where the removal of the early parts come from?

[AndrewSlater]

Thanks for all the positive comments.

If retaining/ returning to mechanical chain tensioners, rather than later hydraulic Carrera tensioners, make sure you use the later type idler arms.

Does anyone know a source for the later idler arms ( and a part number )?
I have the original '74 type but have ordered new sprockets.

will you dyno after the rebuild?

Not sure - but I would like to. However I won't have a pre-rebuild datum as the car was a non-runner to start with.

You have not said anything about the induction system! (cleaned injectors/gaskets etc etc)

I am hoping to keep with the stock CIS. I have been backflushing and cleaning my existing injectors for the last year or so - but still resigned to buying a new set. I plan on refreshing the whole CIS system where possible

Is it worth going to a 2.8L

I'm unsure whether you can to 2.8L with the stock CIS system - would this be pushing it too far? It is also an additional cost with new barrels.

If DIY assembly (good man if you are) then get the Dempsey book

Yes definitely got the Dempsey book

My next question is whether the rocker arms can be rebushed and if so is it a DIY job and where do you source the bushes from?
If not can you suggest someone who can refurb them and what sort of cost this might be?

Thanks as always
Andrew

[AndrewSlater]

So am I right in thinking the later style idler arms are 930.105.509.00 (left) and 930.105.510.00 (right).

If so does anyone have a spare set they are willing to part with?

I guess I also need a spacer to fit them??

[AndrewSlater]

As part of the rebuild I was considering going to a set of JE Pistons to up the compression to 9.5:1.

Does anyone know if I would need to change the cams ( to 964 spec ones ) to get the improvement in power output?

I heard that reprofiling an existing cam isn't recommended, instead use 964 cams but remove the power steering gear. If I were to change to 964 cams ( and get them modified ) would I need to change my existing cam carriers?

Apologies for the all the questions, but when you are spending hours cleaning up your existing engine parts you have plenty of time to think!

As always any suggestions much appreciated.

[neilbardsley]

Andrew how far are you from Surrey and the Fairmile pub are you?

Come down to one of Chris Turner's monthly meetings. Buy him a drink and corner him with lots of your questions?

[impmad2000]

I would be concerned that the CIS system really won't cope with the kind of back pressure pulses that any decent cam will give. I always understood that this engines original cam profile and piston shape were developed because of the CIS injection, and it's limitations.
It sounds like a ITB setup would be ideal, or if budget restrained then Bitz Racing do an electronic conversion using CIS manifolds and throttle, which might do until you are ready ITBs. Or straight PMOs ! Gav did a nice 2.7, but with a "E" on MFI, so doesn't have the same metering plate issues. Good luck anyway.

[AndrewSlater]

I have now had my engine assessment and the list is as follows:-

Crankcase Line Hone
Recommend Shuffle Pin Crankcases
Helicoil x 5 on crankcase
New small end bushes
Cut three angle valve seats
Face chain covers
Helicoil all exhaust studs
Fit case savers
Oil bypass modification
New valve guides

I'm told the Cylinder barrels are reusable as they are but can be re-Nikasil'd.

Does anyone know if shuffle pinning is essential after a crankcase line hone as I was originally advised not to bother with this?
I am also concerned that a line hone might change the bearing size from standard ( which I am told is an expensive change ).

As for the spec of the engine Alan suggested that I keep it all stock. He suggested that if I was to go for higher compression pistons then Wossner were better than JE Pistons ( tend not to suffer from piston slap when cold ). However Wossner don't do a 9.5:1 or similar compression piston for the 2.7 as a standard part.

So given the budget, I am leaning towards keeping the engine stock with the original pistons etc.

If anyone has any advice especially on the shuffle pinning after a line hone then that would be much appreciated.

Thanks
Andrew