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changing valve stem seals....


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Hi all,

I've finally got time to look at changing my valve stem seals on a 12J 2.5nad engine. I've never had much luck splitting the head from the engine and replacing it successfully so i'm going to try this with the head in place.

I've heard the string and compressed air methods of keeping the valve in place, but i've also head that with the cylinder at TDC on a diesel that the valve should only drop about 2mm anyway.

Firstly, is there an easy way on this engine to determin TDC for each cylinder?

Secondly, can anyone confirm the drop of only a few mm?

Thirdy, if all else fails does anyone know where I can purchase an air fitting to replace the glowplug so i can hold the valve up with air?



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Remove the injector and then a thin rod will pass through the the head (there's a hole in the hotspot to allow this). The rod rests on the piston crown and as you turn the engine it will rise/fall. Slowly turn the engine until the rod rises and then pauses before starting to drop again, turn back the opposite way, and you have TDC on that piston) The valve drop is less than 2mm I think - more like 1mm. String in the cylinder is for petrol engines - you shove it through the spark plug hole - not so easy to do on a diesel.


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Instead of the extra work pulling injectors, just watch the pushrods after you've removed the rockers and when both are 'rocking' ie. they both start to move at the same time on any given cylinder that's TDC.

Pop the springs and do the seals.

On petrol engines rather than string you can also use compressed air with an adapter threaded into the spark plug hole.

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Sounds great so far but how will you remove/replace the valve springs without using a spring compressor?. Its fiddly enough getting the collets on even doing it the 'standard' way.

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Sounds great so far but how will you remove/replace the valve springs without using a spring compressor?. Its fiddly enough getting the collets on even doing it the 'standard' way.

Hey all, thanks for your replies.

Les, thanks for putting me straight on the petrol engine stringy thing and the TDC advice sounds reasonable enough for a mortal like me to follow.

Rick, i've removed the injectors already to clean and inspect them and replace the washers seals etc that came with the head gasket kit so no worries there, they look a bit sooty on the ends can i leave them to soak in some petrol or something?

Hi log, i'm going to make up a "gizmo" that will cam off the rocker shaft bolts and hopesully compress the springs enough to get the collets out - will be a bit heath robinson but engine internals are a scary place i dont want to go!

Cheers, and thanks for the replies.

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  • 3 weeks later...

Let us know how you get on.

Right, I know it's been a while since i originally posted, had to keep SWMBO happy and as i'm working abrouad most weeks my weekend time is at a premium!


Fabricated a doo'dah up to press down the springs (will post a picture of it for future reference when i get back home) Basically took me two hours to make out of some spare 20mm box that I'd had lying around in the garage. Works a treat.

The full run down as follows:

1.Removed the glowplugs to enable me to spin the engine with the fan blades

2.Removed the injectors (the thought being to poke some wire through the holes to find TBC - but didn't have any success this method)

3.Removed the rocker assemby in one piece using a bungee cord wrapped round the two end rocker box securing threaded bars to keep it all in place

4.Fitted the bespoke, patent pending (only joking) in-situ valve spring compressor in place (which uses the second small rocker box securing bolts from each end to mount to the block.

5.compressed down the valve spring.

6.spun the engine by hand "gently" till the piston meets the valve and clicks pushing up the valve and releasing the collets.

7.spun the engine each way to fin TDC and then unwound the compressed spring and removed.

8.remove and replace the valve stem seal (note that the inlet valves use the seal with the smaller hole and the spring and the exhaust valves have a larger hole and no spring (in my kit of parts anyway - i reused the old springs on the exhaust seals, didnt think it would hurt)

9. repeat the process for the other valve on the cyclinder.

10. repeat steps 4-9 for the remaining 3 cylinders.

11. refit the rocker assembly

12. refit the glowplugs and injectors.

13. blead fuel to the injectors

14. startup engine, checking oil flows round the rocker box (hint - some oil will get thrown about)

15. refit rockerbox cover with new seal.

The end result is a dramatic reduction of smoke on startup with an almost complete reduction after driving for about 5 minutes. blows out a bit on de-accelerating but nothing like it was before and i never expected a cpomplete cure - just hope it will please mr MOT.

I baught a complete head gasket replacement kit but only used the repklacement items like the stem seals, bits for the injectors washers etc so you could probably just but in the individual bits although the kit wasn't that expendive. NOTE, the exhaust stem seals in the kit were terrible - one was so badly made i ended up using the best out of the old set that i'd removed. when I'l get back i'll have a look see who's kit it was.



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