Bent valves and leakdown

XK-Engine
1

So stupid thing, setting up the 3.4 ‘S’ head that had 6 bent inlets before I purchased it.
Changed all the inlet valves and had them all ground and I lapped them in and did a check with Methelyated Spirits and it all looked good.
Torqued the head down on the new Cometic composite gasket and started timing the cams. Didn’t notice that the exh cam had stopped rotating.
Smashed the innards out of a spark plug and threaded in an ARO air coupling to fashion a leak down tester.
A couple of cylinders had pressure, a couple came straight out of the exh and here is the strange one.
2 of the cylinders are exhibiting noise from the crankcase.
It’s strange as while the head has been off I have been loading the bores with ATF to free up the rings, when I started it went past them quite quickly.
Before I placed the head on the block the ATF was still present (to a certain extent) after sitting overnight.

SO why am I hearing leakage into the sump???

2

Sounds like broken compression rings: only one way to find out.

3

I suppose that’s a possibility, just the oil control rings holding the ATF up :frowning:

4

By design, oil control rings leak down oil.

If the rates of leaking oil out of the bores into the crankcase is markedly different, it’s highly likely you’ve got broken rings.

5

Engine is out and I have checked the valves that were leaking, a VERY light skim on a valve grinder cleaned them up so maybe <>.001” either that or some dirt fell into the seat :frowning:
Next job is to pull the pistons and check the rings. So what started off as a simple head job seems to have escalated somewhat.

6

Neeeext stop: shipwright’s disease!
:yum:

Thanks for keeping is posted!

1 Like
7

Its been a long time since I was this intimate :slight_smile:
All top rings broken and ring width in the pistons for the top ring is about 2.4mm just a bit bigger than the 2.00mm ring thickness.
Custom rings look to be in order :frowning:

image
ACAB11DD-8A41-46CD-B103-1DCAB3949586.jpeg3264×2448 1.69 MB
image
C5A6C544-8882-4E04-9E0E-530DD1B2FE45.jpeg3264×2448 1.66 MB

8

Not custom rings: new, oversize pistons!

Glad you found the problem.

EDIT: that looks exactly like my bench!

9

Not going to that extent, the bores have very little ridge so keeping it stock at present.

10

That’s all well and dandy, but I’m betting the ring lands are worn: make sure they are within spec. With all SIX top rings broken? Stranger things have happened!

11

Only .020” worn Wiggs, no biggie :slight_smile:
Having the piston re-grooved and custom rings made, she’s not going to be a racing machine or concours queen, just a daily runner after the XJR and S11

12

Well, you had better make your top rings with ridge dodger cut out, a little ridge is too much ridge in my book,