Timing CAV. DPA Pumps

[FOWLER MAN]

Hi,
I know the manuals say you need specialist equipment to create a hydraulic lock to fix the point of injection to time these DPA pumps properly, but I've never seen it done.
These pumps are driven by a quill shaft with a master spline so its difficult to get it wrong.
The master spline always lines up with the delivery valve which is receiving the injection and there is a scribe mark on the seal housing indicating the point of injection for No. 1 cyl. These then coincide with the master spline location.
Looking from the drive end of the pump you'll find the mark at 10 to the hour on 4 cyl. engines and 27 past for 6 cyl. engines.

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No.1 Point of injection marks.

If the pump has been fitted to the engine before all that is needed is to line up the marks on the pump flange and gear housing and lock up the three 1/2 AF - 13mm. nuts.
One mm. of rotation of the pump body at these marks represents about one degree at the crankshaft.

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External timing marks.

On a new engine the pumps are individualy fitted before the timing marks are scribed so they are a matched pair.
If you have to fit a strange pump, and the engine doesn't perform, it is possible to reset these timing marks visualy.

To do this you will need to set the engine up at point of injection No.1, and remove the inspection plate from the side of the pump, (two 5/16 AF set screws). You will then be able to see the pump rotor which will have lettered scribe marks on it and a large circlip with one square end.
Slacken the pump boddy and turn it till the square end of the circlip lines up with the scribe mark on the rotor. The mark is lettered A on 4 cyl engines and D on 6 cyl.
Lock up the pump in that position and make your own new timing mark on the pump flange, a sharp chisel does the job nicely.

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Internal pump timing marks

[stevejcb]

Thanks for the info.

What would be the result if the pump was not set correctly - ie: would it run rough, not work or perhaps ruin vital components internally within the pump?

Steve

[FOWLER MAN]

Thanks for the info.

What would be the result if the pump was not set correctly - ie: would it run rough, not work or perhaps ruin vital components internally within the pump?

Steve

Hi Steve.
No, no damage, just stick it on and see how it runs. I haven't done the internal timing thing since I had a pump for a Bedford 330 with no timing mark on the flange back in the 1970s.
It probably wont start so well in the cold and sound a bit harsh if the pump timing is a bit advanced, and it will sound a bit ragged like a partial misfire if too far retarded.

[Doug Reynolds]

This post gave me what I needed to solve a timing problem on a David Brown 950 tractor with a CAV p[ump. The pump was swapped out for what I was told was the original, which I had overhauled. Unfortunately there was no timing mark scribed on the engine, and it has never run really well since I changed the pump. I followed these instructions (with one small wrinkle) and it now runs perfectly. The small wrinkle is that I was not able to find the specification for timing advance, but I do happen to have a second identical tractor that runs very well. So I set the good running tractor to TDC using the pin in the flywheel and took a look at the pump timing marks. The C or G mark (depending on whether you landed on number one or three at TDC - it doesn't matter as they are exactly 180 degrees apart) was 5 mm below the flat circlip at TDC. I put that tractor back together and set the problem tractor the same - 5mm below the mark. It now runs like a champ! I am at the end of the adjustment range, but no matter - it runs great. After more than a year of poor running, despite a rebuilt pump and four rebuilt injectors, my problem is fixed! Thanks for the explanation of the timing technique - it showed me what I need to modify the technique to solve my problem.

[FOWLER MAN]

This post gave me what I needed to solve a timing problem on a David Brown 950 tractor with a CAV p[ump. The pump was swapped out for what I was told was the original, which I had overhauled. Unfortunately there was no timing mark scribed on the engine, and it has never run really well since I changed the pump. I followed these instructions (with one small wrinkle) and it now runs perfectly. The small wrinkle is that I was not able to find the specification for timing advance, but I do happen to have a second identical tractor that runs very well. So I set the good running tractor to TDC using the pin in the flywheel and took a look at the pump timing marks. The C or G mark (depending on whether you landed on number one or three at TDC - it doesn't matter as they are exactly 180 degrees apart) was 5 mm below the flat circlip at TDC. I put that tractor back together and set the problem tractor the same - 5mm below the mark. It now runs like a champ! I am at the end of the adjustment range, but no matter - it runs great. After more than a year of poor running, despite a rebuilt pump and four rebuilt injectors, my problem is fixed! Thanks for the explanation of the timing technique - it showed me what I need to modify the technique to solve my problem.

Hello Doug,
Glad my post was of help.
The early David Brown 950s DPA pumps were fitted with a manual advance and retard mechanism to assist cold starting.
This was opperated by a small screw under the pump body which had a "T" bar through it.
Screwing this out retarded the timing a few degrees.
The position of this cold start screw would affect the internal timing marks and consequently the power.
I have never seen this cold start feature used on any other engines.
Fred

[Doug Reynolds]

Hi Fred,

Yes, was aware of the cold start setting and checked that first. I have tried it on both tractors and it retards the timing the timing so much that they barely run. It really is of no value at all and I have never used it. The tractor I re-timed has never run so well! I have always needed a shot of ether to start both tractors, even in warm weather. It now starts with no ether from cold at temperatures right around freezing. The other one that I took the data from still needs a little shot to start ( which I don't really mind - it seems to save a lot of wear and tear on the starter). However, I have never checked injectors etc. on that one. The one that is now running well has a rebuilt pump and four rebuilt injectors. So after more than a year of running poorly, having spent a bunch of time and money, it is finally running right!

Doug