Who said S2s were boringly reliable?

[zcacogp]

If the engine feels sluggish after the re-build then check your timings carefully - valve and ignition. It runs, so it can't be too far out, but that could be a problem.

Fresh go-go juice will help too, as you say. And it could be just that re-built engines are tight and take a while to release their power! Although yours is just a top end rebuild, this will still apply to a lesser extent.


Oli.

 

[George Elliott]

put a turbo on it....[]

 

[TTM]

George, that could be an idea, but I'm not confident non-forged pistons will handle it fine, even with E85. And I must say I still quite like the "barge motor" feel of that engine

A question regarding camshaft timing : since the distributor rotor moves with the angular adjustment of the cams on the camshaft pulley, would using a timing light on spark plug #1 help to adjust exactly the camshafts with the crankshaft by checking the TDC mark on the flywheel?

 

[robdimond]

I don't think a timing light will help because the ignition timing is controlled electronically by the DME. The distributor just gives the coarse timing (which spark plug).
How did you set up the cam timing, did you use the factory procedure (dial gauges) or did you lock the cam sprocket to the propeller behind it?

 

[TTM]

I removed the camshaft pulley to replace the seal without noting down the position, so I lost the exact adjustment and put it back together loosely basing myself on the spots left by the 3 spacers on the camshaft pulley.

As far as I know ignition timing is dynamically adjusted by the DME in function of engine load, but the ignition value when the engine idles should be fixed - unless there is some idle ignition table that becomes active when TPS = 0%, but I doubt it.
Even in that case, given that my engine idles at a perfectly stable speed, then it means the idle ignition value should be fixed and a timing light may help...?

 

[robdimond]

My thinking is that changing the cam timing by a few degrees will not change the ignition timing... so you won't be able to see any difference. The DME is going to fire at some point when the rotor is passing the connection on the distributor.

I think you'll have to do the factory procedure...

I did read about a guy with a 968 who got the wrong number of chain links between the cams so one of the cams was out. It still ran and did no damage, but was down on power. Maybe that's worth checking as well?

 

[TTM]

The camshafts and the chain stayed together during the whole operation - I'm confident they are correctly adjusted.

If spark duration is "too long" then for sure a timing light won't help. Anyway, will try something...

 

[TTM]

So the timing light didn't help much, but it taught me a standard S2 engine runs about 10° of ignition timing at tick over.

If I increase the timing on the camshafts, this should shift the engine's torque band to higher rpms, right?

 

[Jonny944CS]

Broadly speaking; retarding the inlet cam timing should help volumetric efficiency at ~ 4000rpm plus

Advancing inlet timing and increasing overlap with the exhaust event helps in the lower speed range 1500-4000rpm.

Both of the above assume that the Exhaust timing is fixed. Things become slightly more complicated if both intake and exhaust are moved together.


A good-old dial gauge on the tappet and piston + the factory WSM timing procedure should reveal all.

 

[TTM]

I spotted a small mark on the camshaft pulley, which was most certainly done previous to my ownership and that I hadn't noticed before due to lack of attention, suggesting how the pulley should be aligned with the 3 bolts for the rotor.

I aligned them together and it would appear that I have found the sweet spot - the engine is now nicely responsive all through the rev range.

Before all this I used to feel a light kick in the back when going past 4000 rpm under full load, which would now appear to have turned into a plateau during from 3600rpm to 4000 rpm. The engine is overall more responsive and slightly more torquey below 3500 rpm at any load, which I put down on cleaned & matched injectors, a fully cleaned intake tract, and also perhaps on properly-sealing exhaust valves - the machine shop that rebuilt the head mentioned reworking exhaust valve seats as exhaust valves did not seal properly.

Everybody loves a happy ending []

 

[robdimond]

Great news! Very glad it all worked out in the end. Hope you have a boringly reliable few years...

 

[TTM]

Thanks Rob.

I did a straight 300 mile drive on Friday night and it didn't miss a beat, reminding me of the best travels I had with her in the years shortly after I bought it ten years ago... But the old girl seems to want further more already, I can hear a very low frequency noise from the rear, which I think is certainly a wheel bearing. Oh well, at least she's now taking a progessive stance in the way she expresses her complaints []

 

[zcacogp]

Good news TTM - bravo!

You can now go out and munch those pesky turbo's for breakfast again ... []


Oli.