Engine Leak Tester

[Bruce Tuncks]

I like Nev's comment about cheap insurance, so with my 500 hour engine I now have another worry. Do I really need to replace the valves? What are the odds?

 

The examples of "soon to fail" exhaust valves in the Busch article show a non-concentric pattern of deposits and colours. This would indicate it was warped and warpage should be evident in a leakdown test too, as the valve would not be seating all around. I wonder how these cylinders would have felt on the turnover test that morning.

 

 

[jetboy]

I have a 2200 and replaced the exhaust valves at 300 hrs as a precaution - the leakdowns showed 2 cyls with slight exh. port seepage in addition to the usual crankcase blowby.

 

The valves were OK - some pitting on the contact faces which could have been ground out but its easier to pop new ones in. more importantly the usual catastrophic failure seems to be at the stem necks many reports of fine radial cracking in that area esp. with lean running

 

So when I needed to pull the heads again at 500 hrs to correct the rings blowby I replaced the exh. valves once more- with Camit sourced ones as per the 2200 original build type. There was nothing wrong with the valves its just more risky to leave them in if the heads are coming off anyway.

 

Also noted that daily pullthrough can be variable and ofte - like last week - poor results on 3 cyls but after a couple of hours checked today and its all normal. like leakdown results you need at least a second flight to recheck before strippng it down.

 

 

[Yenn]

The latest, out today from CASA is that the gauge needs to be calibrated. That is from Skidmore himself.

 

I wonder about CASA. When a leak down test is comparing flow in to flow out, I cannot see that calibration of gauges is relevant. If the gauges are out by 10% you are still comparing the differences. Using the same gauge at easch inspection, you will have the same differences, so it is of no consequence.

 

 

[facthunter]

The rate relates to piston size and they want a figure, so the hole has to be exact. Nev

 

 

[Bruce Tuncks]

A characteristic of the leakdown test is that the figures it produces are not repeatable unless something big has happened. I have to admit that when the valve-seat fell out, the figure was zero for that cylinder and it sure was repeatable.

 

Well it looks like I need to order 4 valves on account of them being there for 500 hours.

 

I'm also going to modify my USB camera to look back up its cable to see the valves, but of course you wouldn't see fine cracks at the stem-base until you took them out.

 

 

[jetjr]

You can get a camera whch turns back on itself

 

Mirrors on normal usb wouldnt work for me

 

 

[facthunter]

Bruce , do a proper repair on that valve seat insert, if you are not replacing that head. Nev

 

 

[Bruce Tuncks]

Yes you are right jetjr, there is a good-looking camera end to do this. It's a bit expensive for a cheapskate though compared to the $20 ebay camera I have, so I'm going to try a home-made thing first.

 

You are right about the mirrors, I couldn't see anything much with the mirror attached but the view was ok without it.

 

Right now I'm busy with the home-made ECG gauge business, with great help from Mark Kyle from this forum and others. So those exhaust valves will be waiting just a bit.

 

And yes you are right Nev, I don't feel relaxed flying with that head, it's had about 5 hours since the event but I don't have confidence in it any more.

 

 

[facthunter]

Trouble is ALL the heads would have gotten hot. It's not difficult to remove all inserts and check fit and replace with slightly larger ones where needed. I prefer to use cryogenic process. They always did with porsche heads (when done properly). Nev

 

 

[jetjr]

The hard part is getting a camera that will go down an 8mm hole

 

Could cut outer cover leaving a floppy section, with string tied to the end, after insertion into cylinder pull the string folding camera back on itself

 

Fairly good risk I would cut right through and ruin it

 

I just bought proper one from US when dollar wasnt too bad.