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MG MGF Technical - Hydraulic Tappets

On dissasembling a head, I noticed that the spring which is inside the tappets, doesnīt work anymore. It is simply stuck. Whether it is stuck open or closed, I donīt know.
Has anyone obsered this as well? Any
remedies? when pushded, the spring only actuates on 4 /16 tappets
cheers,
david.
David Peters

Peter the spring will not stop the tappet from compressing it is hydraulic pressure that is keeping the tappet pressurised, the other 4 have bled down.If you want to clean the insides ot simply pull the centre section out with a pair of grips.
mike

David,
you should bookmark until you've finished the engine works
http://hometown.aol.com/dvandrews/kengine.htm
;-)
Dieter

Hi Dieter. That was one of the first URLS in my bookmarks. Printed the lot couple of months ago.
Before bedtime I used to read a few pages (when the Mss grabs a book)

Mike, I Canīt figure out where the oil pressure works on the tappet though. To leave it to stick "compressed", there should be pressure from the outside (from underneath actually) against the spring.
Some I can push with my fingers, others not, hence I figure they are stuck in a compressed position.
But probably I have the workings of the tappet and oil flow within missunderstood. Iīd like to find some throughcuts to grasp it though. I hate working on things I donīt understand the working of.


cheers,
david.
David

David,

I have worked with Hydraulic Valve Lifters from a Saab 9000 Turbo 94 model and I had posted some info as how to clean these.
Here is a link to a Saab forum that you may find helpful.

http://www.saabcentral.com/forums/showthread.php?t=30961

Also if you want to learn a bit about these things (and it looks like you do), here is another link to some good info.
http://www.cranecams.com/?show=faq&id=3

Cheers
Branko.



Branko

Thanks Branko! Good info.
cheers
david
David Peters

Peter, some of the advice shown on these pages are not appropriate for the MG tappets, if you have done any work on the head such as recutting valves etc the preload on each tappet will have changed. This can prevent valves opening correctly on start up or even cause difficulty in starting due to loss of compression.Bleed down each tappet(do not fill them with oil as they may pressurise up solid)and turn engine over with plugs out and the coil disconnected till oil pressure is up.
mike

Thanks Mike, I am merely investigation the differtent parts of the head, not doing any recutting on valve seats, etc. wouldnīt know how to measure the (3)angles, let alone doing it properly with hand tools.
If it happens, itīll have be machined.
I am wondering though if Paul Ivey valves have any effect on performance with a stock (maybe quick port and inlet port matched) head?
cheers,
david.

David.
David

David, just changing the valves for REC valves, as good as they are, you would not notice any real gains in power or torque, maybe a drop in torque with that particular valve design at lower flow rates. If you are going to do any port work and are changing valves to a larger dia. on the same seats then careful detailed work is required as the valve sits on the top edge of the seat and the seat width is some 1.3mm. One careless move with a carbide cutter and the seat is scrap. Either replace the seats with a larger diameter seat(assuming your head is a non VVC) and use a modified VVC inlet valve or use the stock 1.8i valve with modifications and suitable seat angles and valve seat contact width set at 1.3mm together with throat and port work will give good results.
Mike

Would 1.8K turbos gain from REC valves?

Arenīt Paul Iveyīs valves straight fit in the mpi seats?

From what you are saying Iīd deduce that it is not because the seat width is 1.3mmm that contact witdth is 1.3mm, thatīs why the seat needs recutting.

I guess valve seat recutting is done one a mill programmed to the specs? So it can be done virtually in any workshop undertaking work on different brands of engines (heads)?

Getting way off topic here! Sorry guys,

cheers,
david
David

David, maybe I didn't explain correctly, the valve sits on a metal insert or seat , this has to be machined to suitable angles so the valve contact area is to specific dimensions, one of those dimensions is the width of the contact area usually specified so the contact area on the valve is 1.3mm wide. The height of the valve has to be set as well otherwise the valve lift will be incorrect and defeats the object of any improvements made.Accurate seat and valve cutting is paramount to good performance gains because compression can be lost past the valves.Narrower seat contact area gives higher sealing pressures but also less room for errors.If you are wanting to fit another valve then my advice is to make sure the machine shop has all the relevant fitting specs for that particular head. Valves should not need lapping in in the convential way using the lapping in paste you buy from the usual sources, it is far to course, even the 'fine'. Seats/valves recut using carbide cutters on a programmed machine should be accurate enough for reassembling without any further work. That said we use a special paste, similar to tooth paste in texture,ie. you cannot feel the particles when you rub it between your fingers.
In answer to your question regarding turbo application
if you are converting a stock head to a turbo then I would fit larger exhaust valves of a higher spec than standard.I would suspect Rover fitted a different spec valve in their turbo engines.
mike

Hi Mike,
I thought the valve seat was part of the casting. But appearantly it is not.
I am getting the right tools this week to get the valves out, then I will definately see what you are referring to. But it seems to be clear now! thanks the the explanations.
In the EPC I didnīt see any difference in valves between turbo and non turbo. I would have though the REC valves have much better and more efficiënt exhaust flow. Iīll have a read tonight in Bellīs 4 stroke tuning book, which covers quite a lot on the subject,
regards
david
David

This thread was discussed between 26/02/2006 and 01/03/2006

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