IP Timing and Cold Start

[ian2000t]

Borrowed a proper set to check the IP Timing which screws into the pump so gave it a check tonight (1990 760 D24Tic - UK spec).

What I did was crank the engine over a few times, setting the gauge to 0 at it's lowest reading. Then cranked it over to TDC.

The gauge read 1.03mm. Then I realised I hadn't disconnected the coldstart... so I disconnected it and did the test again - I got 0.98mm.

So... I take it the cold start must advance the timing? Think is, this is on a properly hot engine, so that means my Cold Start is always engaged a little bit. It's also adjusted to the end of it's cable.

Something doesn't sound right there to me. Any thoughts?

Also, what should the timing setting be for my engine?

[ngoma]

Cold start advances the timing and bumps the idle up a bit.

Check to see the cold start lever moves toward its stop as the engine warms up to operating temp.

The cold start thermostatic actuator is a wax pellet operated mini thermostat (similar to common cooling system tstat). It is inside the barrel that the small cooling hoses attach to. It works against strong springs that want to pull the cold start lever to the advance position, so when the thermostatic actuator fails, the cold start mechanism wants to stay in the advanced mode, even with the engine hot. Bad engineering decision, it should have been designed so a failure leaves CS lever in the normal (non-advance) mode. If your cold start lever does not return to the lever stop when warmed up, the actuator wax pellet might be failing.

[ian2000t]

Yeh, sounds a terrible design! I'm pretty sure mine is doing sweet FA, as this was a completely hot engine (just done 10 miles stomping on the smoke pedal). It's been sat cooling 40 mins since I got home tonight so will check if it has moved any.

[ian2000t]

Right, when the engine is fully hot it is slighty activated. To deactivate, you have to disconnect the cable.

When the engine is fully cold (engine off for 5 hours and about 10 degrees C outside.....still exactly the same position.

So... basically its shafted! Is it easy to repair? I'm tempted to stick a cable in and use as a manual choke!

Is 1.03mm too advanced? If so, is 0.98mm ok (what its set to with cold start off)?

[v8volvo]

You don't want to run with it in cold advance mode all the time -- not good for the engine. Disconnect it and leave it unhooked until you can fix the automatic advance system or devise another solution. It will be a bit rougher on initial cold start-up that way but that's better than endangering the motor's health. Don't forget to re-tighten the little screw in the cable end piece after you put it in the disconnected position, though, or else it will vibrate loose and fall out! It's not the most important screw to have, but they are expensive to buy so it's worth saving yours if your car still has it...

One other thing of note: after releasing the cold start advance lever from its advanced position, the internal bits inside the pump that that lever works against (the roller cage, specifically) tend to not spring fully back into their normal position until you turn the motor over a bit and the pump has a chance to work things around. So, if you measured 1.03mm then released the lever and got .98mm, that is probably not an accurate measurement unless the cold start was only on a little bit. The cold start being pulled forward usually advances the timing by .20mm or more (measuring plunger travel at TDC), so if your base timing was .85 (factory book setting) and you applied the cold start you would be at around 1.05mm.

In other words: the 1.03mm you measured is accurate, but to find out what the timing really is with the cold start disconnected, you need to do more than just release the lever and see where the dial gauge moves to. You need to do that, then turn the engine through a full two rotations, back to #1 TDC, and see what the measurement is then. This gives the pump a chance to turn a full revolution and work all the parts inside back to their normal non-advanced positions, so that the reading you get at #1 TDC after turning it over will be the real, unaltered basic timing setting.

That setting should be roughly between .85 and .95 mm. .98 would be a little high but basically OK... but I think you are probably actually lower than that, after you check the timing as I have described above.

Let us know what you find out.

FWIW, the wax thermostat isn't that hard to replace, works well, and lasts 10+ years... I think it's worth replacing!

[ian2000t]

Thanks for your reply.

The cold start was only stuck on a little - now disconnected. When the engine is running and I pull the cold start on manually it does get rattlier.

I tried to check the timing again yesterday and it's really weird...

I turned the engine over a few turns and tried again - seem to be getting a reading of 0.95mm. I've put some biodiesel in (different story) and it seems to clatter more but I've read it burns faster so needs slightly retarded timing. So - I was going to retard the timing to 0.85mm. I read the easiest way was to turn engine to TDC, undo the rear cam sprocket and twist it until the pump shows the figure you want, then do the cam sprocket back up.

I didn't actually get the cam sprocket undone, because I couldn't lock it from turning well enough. What I did find though, is that turning the cam sprocket slightly alters the timing between about 0.80mm and 1.00mm without the crank turning from TDC. I am talking a tiny amount of physical movement on the cam sprocket though. Does this mean my cambelt doesn't have enough tension on it, allowing the cam to move slightly independantly from the crank, or is this normal?

Do you know where I can get the internals to fix the Cold Start?