2006 MINI Cooper burnt exhaust valve

[one eyed mick]

Ok I don,t have the out and out experience of MrPuma racing and most of my work in 45+years has been on run of the mill stuff and large deisel engines [ up to12 litres] but having to use pre used stuff , cutting both seats and valves myself taught me a lot including the factory prefered system from ford where if seats were either new or refaced well and valves were new a simple tap on the valve head when seated with a 1lb hammer was deemed to be ok , the ultimate is either 3 angle or very small radius seats but in the realworld unless money is not a problem it is the old fashioned way that is reliable . I have seen many instanses of the op orig prob ,caused by many things inq incorrect valve clearances, poor valve manufacture , excess guide wear ,debris from pistons , incorrect air filtration and numerous others . I will still lap seats the way I have always done and was taught to do many years ago

[PeterBurgess]

Hi Mick

I trust you are well? I cannot remember which diesel engine manufacturer it was but we had to do a ringing test to check for sealing, new valve on sucky stick then tap down sharply on seat, if leaves a good ring on valve and seat all is good, they did not want any lapping pastes anywhere near seat for fear of contamination. Modern titanium valves with coating on seat area, engines die a rapid death if lapped so we have to blue the seats and valves only, they are revving at around 14000rpm. I must admit I prefer to have a nice grey ,lapped finish, feels natural somehow. I also understand the Mini R50 ex valves are not maybe as high a quality as they could be and the R53 sc ex valves are a better bet but I am not really familiar so do not know for certain

Peter

[Ian_UK1]

It may also be worth pulling the fuel injectors and having them cleaned and flow-tested. It's just possible that the cylinder with the failed valve was running leaner than the others and the higher combustion temps were instrumental in the failure of the valve. For the cost and time involved it can't hurt and it will also restore the injectors' correct spray patterns (to the benefit of smooth running and fuel economy) even if nothing else is wrong with them.

[Pumaracing]

one eyed mick said:

20 secs of lapping ? you might aswell not bother, after about 45 years of experience that is bull pucky, do the job properly !!!,if new valves and seats you should not need coarse paste , if seats and valves have not been surfaced you will need minutes of coarse and fine to get any thing like a seat !!!!

I suggest you get a scrap head, a good valve preferably freshly refaced and see what happens when you lap in for ages as you suggest. Put a straight edge across the 45 degree valve face, the shank of a vernier caliper is ideal but a good new drill bit shank or milling cutter will do, hold it up to a bright light and see what you see.

Then get some engineer's blue and very lightly blue the seat in the head and check where it makes contact with the valve. It'll only be on the edges. Then clean them both up, blue the valve and check the seat. Again it'll be concave.

Lapping can never properly compensate for seat wear or eccentricity. On ultimate engines I don't even like to use the valves that are going to run in the engine when I do a 10 second check lap for proper seating. I use spare scrap valves freshly refaced to check lap the seats in the head and then the proper valves get fitted straight off the valve refacer which has already given them the perfect seating surface and anything further done to them can only make that worse. I happily admit this may be unnecessarily anally retentive

[one eyed mick]

Hi Peter , yes have used the ringing bit my self when working mainly on Magirus Deutz air cooled oilers ,at one time I was reconing heads daily i.e. strip clean, new guides, recut seats and valves and possibly new valves ,each cyl had it's own head , singles ,twins ,3's ,4's 5,s and sixes the bigger v stuff 6,8 ,10 ,12 where the samebut meatier heads .
pumarace
as said your work is /was on a different level to mine but basics are basics a who in their right mind would build a head up with out checking seats for ovality ? I was building for long term reliabilty and as far as I recall I had very few come back ,inthe order of 2 heads out of possibly a thousand or more not race screamers but engines that worked possibly 18 hrs a day 7 days aweek I also have great respect for guys like your self and many others but still contend that proprly lap valves and seats work

[Si1295]

PeterBurgess said:

I also understand the Mini R50 ex valves are not maybe as high a quality as they could be and the R53 sc ex valves are a better bet but I am not really familiar so do not know for certain

Correct, R53 valves are exactly the same size but are made of inconel which would have helped in this situation

[Pumaracing]

I would only say that many engines are routinely tuned to deliver much higher specific power outputs per litre than the stock Mini engine and run very happily on stock quality 21/4N exhaust valves. Inconel isn't really needed except in the most exceptional situations. I suspect manufacturing quality is the root of the problem here rather than material spec.

[Jimmyarm]

Thought I post that (working as a spanner monkey) I've seen first gen mini's with burnt exhaust valves a couple of times in the last 5 years or so.

One of them had very worn cam lobes as well, a reasonably common problem apparently.

[PeterBurgess]

Hi Mick

Have you used one of these run out gauges? We tend to use it when we are dealing with applications where the valve to guide clearance is fairly large such as in turbo applications, it is probably more accurate than lapping or blueing at that stage.






Peter

Edited by PeterBurgess on Monday 10th November 14:36