Dropped Valves In Mi16 Motors?

[Normski 1]

As per title.

How much of an issue is this with other Mi16 users?

 

The reason I ask is, I've had 2 apparent valve failures with my Mi16 motor and I wondered if other users had any issues with this?

 

Now, my car is only used on track and has the standard rev limit (~7100 ish), but even so.

The car had about 2.5 seasons of track action (~ 25 days) before the first failure which I think the inlet valve failed just below where the collet grips. The engine had done 70 odd thousand miles.

 

After that I renewed all the valves and put the engine back together.

 

1.5 to 2 seasons later and another inlet valve failure, this one looks to have failed where the valve head meets the stem.

 

Am I expecting too much from the standard valves? (std rev limit, not over rev'd).

 

Is there an up-rated one piece replacement? If so, how much are they?

 

Thanks.

[PumaRacing 2]

Badly cut seats that aren't properly concentric can cause valve failure. Any chance you had the head reconditioned before this started happening?

 

The standard inlet valves ARE one piece. There's no reason they should fail if everything else in the head is ok.

[welshpug 1,657]

are they simply breaking off? or are they getting overheated then breaking? ( easy to tell as the metal gets tarnished/discoloured)

 

might be a case of oil starvation/overheating.

[Normski 1]

Before the first one, the head was untouched by me and I don't think it had been reconditioned by previous owners going by the mileage and condition but I don't know.

That first failure caused a fair bit of damage to the chamber of that cylinder, so I was advised to get another. Which I did. The next head was then insepcted/reconditioned and I built it up with new standard valves.

 

I have the first damaged valve in front of me and it's in three pieces, the valve head, the stem, and 5 or so mm of the collet area. The head has a large amount of blue/purple colour.

 

Is the quality of the standard valve up to this sort of use? Going by A. Graham Bell's book, the material of the valve should be non-magnetic if it's any good (these are magnetic)?

[welshpug 1,657]

if its gone blueypurple that definitely sounds like overheating.

[Normski 1]

What would be the cause of this overheating?

 

The stems not discoloured only the valve head.

 

The engine oil and water temperatures are stable and are at the right temperatures.

Before each failure the engine has been working really well.

[Dazza 4]

I think its like this bud imo;

The first failure could have been poorly overhauled before you bought it or a bent / damaged valve sticking in the guide at the collet end and eventually wore the collet groove to failure ?

The second failure imo is as puma say's it sounds as if the valve seat isnt seating propperly hence the burn/gasses is passing into the inlet chamber to a point its degraded the strength of the valve head and eventually broke the head off ,it could be a possibility that all the inlet valve seats are poor ? have a look .

If its been stripped and all the valves mixed up and basically lightly lapped and built up then this sort of damage will occur time on time .Dazza

[Normski 1]

I don't think there has been a sealing problem as the engine has been performing so well before both failures.