964 Rebuild going well until we broke 3 rocker arms

[Alex Sol]

Fellas,

I started rebuilding the 964 in November and have progressed nicely until last week.

My mechanic (and I) dropped the engine and transmission and proceeded to strip the engine down to its two shells. All gaskets, seals, bearings were replaced in rebuild.

In addition, the cam gears, chain, chain guides, were all replaced.

Heads were brought into a local shop and guides and springs were replaced. I kept the original valves and rocker arms as they 'would last longer than me'....

We put it all back together, with new clutch and release bearing.

Cams were set to +4 degrees and motor was running nicely in the shop. Smooth idle purring like a kitten.

Clutch was bled and slave clutch cylinder was replaced with new.

took it for the long awaited test drive last week (mid April) and the clutch and gear box were tight. Previously slipping like crazy and the engagement point is now very direct and distinct.

The motor would not rev up but rather seemed to labor.

We brought it back to the shop after a drive around the block. Reduced the Cams back to +2 degrees to see if we could open up the motor.

Took it out and it stalled. Started it again, drove it around the block and the motor would still not rev freely.

brought it back to the shop, turned off the ignition and tried to re start.

The motor would not turn over and after a few attempts, bang!!! Sounded like a back fire and when we put it back on the hoist, we removed the cam covers and found #1,2,3 exhaust rocker arms broken.

Now when we try to hand turn the motor, the cam shaft will not spin.

That's as far as we have gotten.

I appreciate any comments on this situation.

[Alex Sol]

oh almost forgot, we replaced the distributor, plugs, wires and rotors and put in a new belt with vent kit...

[john walker's workshop]

i guess you need to set the cam timing with the proper dial gauge to the proper spec. stock cams?

[Alex Sol]

i don't think we have such tools but the cams are stock. does that mean anything. it seems we 'lost' a semi-circle shaped washer or 'key'. We have ordered the part and will see what happens.

[cgarr]

Did you get one cam 180 off? Was one sides exhaust cold?

[Alex Sol]

good question cgarr. no i don't think the cam was off 180 deg... the car had been started many times before we took for test drive. it was hunting for idle under 1000 rpms at first as we forgot to hook up the 'vacuum / air' hose (not sure of the real name) right under neath the throttle cable assembly. Once we hooked it up and clamped it in place the motor purred beautifully for at least 10 min. while burning off some serious oil in the exhaust which found its way right into the cabin interior. After some most of this oil was burned off and cleared out with fans blasting full we took it for a test drive.

the throttle response was quite sluggish and the engine would not return to idle but stayed above 1500 rpm. Also the revs dropped very slowly compared to normal. we made the adjustment on the left side and the exhaust was hot. previously the cat was burning hot and after we found that air hose hanging and inserted it into the inlet right next to the throttle cable assembly it was running normally. now that i think about it i did not notice if the driver side exhaust (cylinders 1,2,3) were hot or not.

[john walker's workshop]

you will have to remove the set of heads on that side, disassemble, and remove all the valves to check them for being bent. do it now so you don't have to do it later. and get the dial gauge and go through the proper cam timing procedure this time. a metric dial gauge. so the cam key was missing before or after the problem?

[Alex Sol]

Thanks John,

what does the key do? It may have been missed on the rebuild. Engine is back down and heads are being removed to inspect for bent / damage valves.

what does the cam timing tool look like? is it the 60 degree measuring device?

[MatthewBrum]

I hope you are not talking about the key that keeps the cam sprocket fixed to the cam. Consider yourself very lucky if no valves are bent. If you do not have a copy of Waynes 911 Enginer Rebuilding book or the Bentley manual you should get one ASAP, you will find it invaluable.

[Alex Sol]

the wood ruff key. looks like one of the lucky charms cereal.

a one dollar part was missing / lost or broke. i think it is in the bottom of the motor now and the exhaust valves were bent and smashed the rocker arms. picked up the part this afternoon and have Wayne dempseys book and Streathers 964 companion.

picked up the exhaust valves and will put it all back together.

[Alex Sol]

Quick update:

replaced the exhaust valves, replaced the rocker arms and found the wood ruff key. Installed and reset timing.

rocker covers and cam covers all replaced

Intake re installed

re hung the motor

connected the drive shafts

starter motor

connected the exhaust, cat and muffler - new copper lock nuts - they look pretty

hope to connect the rest of the little bits - distributor and plugs, various hoses

add back about 5 litres of oil that came out of the left side (1,2,3) cam (very little from the right 4,5,6 cyl)

any other suggestions before firing up?

[john walker's workshop]

how did you set the cam timing, and to what spec?

[Alex Sol]

John,

My mechanic buddy set up the cam timing using the notches on the flywheel. I'll get a little more detail on this.

[jjrowe]

Alex,

What John is alluding to (I think) is that you cannot set cam timing with anything other than a dial guage and the proper holding tool. Ignition timing is set using marks on the crank pully. Maybe there is a disconnect here between you and your mechanic, but he apparently already forgot to reinstall the woodruff key so you can't be overly cautious. Make sure that the cam timing was set using a dial guage and get the spec he used so you don't bend your valves again!

Jesse
76 911S

[john walker's workshop]

notches on the flywheel? you might want to try a different guy.

[engguy]

John, on your site it says your a one man shop?

[john walker's workshop]

that's correct.

[JFairman]

964 cams should be set at 1.25mm
With new chains and sprockets you could set them to 1.26mm (very little difference) and they'll be at 1.25mm after a 1000 miles from the chains breaking in..

You need the metric dial gauge with extension rod and Z block to mount it on the cam towers with the extension rod properly set on the highest part of the intake valve spring retainers on #1 and #4 cylinders.
There is a procedure to follow and then you need a special tool to hold the cam sprocket from turning while you tighten the 19mm bolt or 46mm nut depending on what year your car is or the year car the cams are from.

Originally Posted by Alex Sol

John,

My mechanic buddy set up the cam timing using the notches on the flywheel. I'll get a little more detail on this.

I hope that's a lack of communication...

[dtw]

Been dying to know how this turned out... any updates?

[Don Settergren]

Yeah, bring on the carnage!