12J exhaust peak timing

I am based in Ireland and have a 1985 90 with 2.5NA engine 12J. I am putting the engine back together following a problematic timing belt change (threads damaged on some studs). During the process the crank was accidently moved and I am now unsure about the timing marks. I want to ensure that the injection pump is correctly aligned and not 180 degrees out.

I understand the 12J is timed based on exhaust peak (number one cylinder), although I am unclear on the precise meaning of "exhaust peak". I assume it is the mid point between the exhaust valve starting to open and then fully closing. I also understand the key-way on the injector pump shaft should aligned with the cylinder one outlet pipe on the pump when cylinder one is injecting.

I have checked the pump fitting and it aligns with my understanding of the exhaust peak criteria and also the shaft keyway roughly aligns, however the engine will not start. Is my understanding correct or flawed.

Did you start this job with a timing [locking]kit? or just position the pully's against marks, early 12j and later 12j have different timing methods. Early 12j cranked is timed through window [like 10j] in flywheel housing where marks can be seen against a pointer. Later 12j has a plug in the housing that a special tool [ plug with spring loaded pin] that engages with a slot in flywheel to lock at TDC.
The term exhaust peak with regards this engine is the EP mark you can see through the flywheel window. When you reset crank after movement what did you do? It is important to turn engine clockwise if crank position is lost and not turn back.

tottot said:

Did you start this job with a timing [locking]kit? or just position the pully's against marks, early 12j and later 12j have different timing methods. Early 12j cranked is timed through window [like 10j] in flywheel housing where marks can be seen against a pointer. Later 12j has a plug in the housing that a special tool [ plug with spring loaded pin] that engages with a slot in flywheel to lock at TDC.
The term exhaust peak with regards this engine is the EP mark you can see through the flywheel window. When you reset crank after movement what did you do? It is important to turn engine clockwise if crank position is lost and not turn back.

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Thanks tottot, My 12J is an ex MOD reconditioned engine. I have the engine for about 18 years and overall it has performed well.
I recently replaced the cylinder head gasket after an overheating incident and afterwards it was not running well and was more smokey than usual. I suspected a fuel related issue and that the pump might need a small adjustment due to a small compression change with the new head gasket. When I attempted to adjust the pump, the threads were not good on the pump securing bolts and as it was due a timing belt, decided to replace the belt while repairing the screw threads in the casing.

The flywheel has a timing slot and there is also dot on the crank pulley. I do not have a spring loaded pin but have used a TDI pin which is not a perfect fit but very close. With the pin inserted, I can get the dots on the crank, cam and pump pulleys all to align with their respective arrow heads on the casing and can also insert a pin into the pump in roughly the middle of its adjustment range. (all good except I am unsure if I am in phase or 180 degrees out).

In general I rotated the engine clockwise with a possible small anticlockwise due to overshoot close to the timing marks.
This evening I discovered I may have a fuel lift pump issue in parallel which I will investigate tomorrow morning.

I was cautious about the original timing marks but had a small issue/accident that caused me to loose alignment.
The threads on timing belt tensioner bolts were also poor. (In the past someone over enthuastic with a torque wrench.
I ran an 8mm tap through to clean the threads. When I tensioned the new belt for the first time, one stud entered too far into the casing and restricted the full rotation of the engine, when hand cranking to tension the belt for a second time. (sorry about the long background story).

I guess the pump alignment is a 50/50 possibility. The CAM alignment should not matter since it does not know if the engine is in compression or exhaust stroke and it should be symmetrical. If it does not work, I can always try the other option, but was trawling to see if there is a more scientific way to verify the pump alignment with visibility of the tappets.

If fuel lift pump is poorly then that can result in poor running, even with it not working [ split diaphragm] engine will still run
When you say " pump alignment" do you mean crank? Pump and cam pully's just line up dots with pointers on case. Should one go past the alignment point on the flywheel one has to do 2 revolutions to get back to correct positions. So if you are guessing it is a 50/50 chance. But if you have pin locking the flywheel and cam pully and injection pully on their pointers with belt tensioned then that is correct. Any time you do work like this turn engine over twice by hand to see all is free.

The fuel lift pump was faulty and I have ordered a replacement. I guess it was weak, but working, until I disturbed the injector pump. It was unable to lift the fuel when restarted. Replacement expected tomorrow.

In relation to timing, yes, I mean the relative position of the crank to the pump/cam. Even with all dots aligned and with the pin inserted it is still possible to be out by one revolution of the crank i.e. 180 degree relative to the pump.

Will update when I fit the replacement lift pump. Many thanks.

I am still awaiting the replacement lift pump, but in the mean time, through brainstorming on-line, and further reading, I think I have figured out the answer to my original question.
The 12J timing is based on exhaust peak (EP). A Land Rover service bulletin for Series 1, that I saw online describes exhaust peak as "exhaust valve at peak lift i.e. fully open". Other on-line threads on this forum specify EP at 109 degrees BTDC for the 12J engine. TDC is not marked on my engine, however I dont believe it is important for my issue.

In summary, I think if the CAM and Pump timing marks are in their correct position, and if the Crank mark corresponds to the No.1 cylinder exhaust valve at or near its peak lift, then the timing should be o.k. and not 180 degrees out. I will verify this reasoning when I fit the new lift pump.

Danduck90 said:

I am still awaiting the replacement lift pump, but in the mean time, through brainstorming on-line, and further reading, I think I have figured out the answer to my original question.
The 12J timing is based on exhaust peak (EP). A Land Rover service bulletin for Series 1, that I saw online describes exhaust peak as "exhaust valve at peak lift i.e. fully open". Other on-line threads on this forum specify EP at 109 degrees BTDC for the 12J engine. TDC is not marked on my engine, however I dont believe it is important for my issue.

In summary, I think if the CAM and Pump timing marks are in their correct position, and if the Crank mark corresponds to the No.1 cylinder exhaust valve at or near its peak lift, then the timing should be o.k. and not 180 degrees out. I will verify this reasoning when I fit the new lift pump.

Click to expand...

The summary above is confirmed. New lift pump fitted and engine running again. I had a lot of difficulty bleeding the injection pump, but eventually got the air out after changing a few fuel lines and opening the pipe going back to filter while cranking.
Will fine tune the timing this afternoon and put everything back together. Many thanks.

180 out and it would not go. Not sure how much fine tuning one can do with a 12j other than check marks are on the money after a bit.
I had a 19j and part of the cam belt change instructions said, ensure sprockets are all on their timing marks, feed belt over pully's then going from crank to cam pully then to injection pump pully, engage belt teeth maintaining tension. [ here's the fun bit ] " if belt teeth do not line up turn pully some clockwise to engage".
Anyway glad you are sorted.