While i had the engine out of the car to change the cam i thought i'd do a leak down test as it was by the compressor. I did the test on a cold engine, all cylinders gave results less than 10%. HOWEVER on cylinder 4 i did hear/feel a slight leak through the intake, valve was definitely closed. All cylinders i could hear a slight leak past the piston but because the overall value was <10% i assume that's normal?

So my question is, is any leak past the intake valve (like i have on cylinder 4) acceptable? If the answer is yes, great. If no could some light lapping help, machining required or would i not know until i remove the head (not taken it off yet)?

Thanks
Glenn

How about gluing a piece of balloon rubber across the exhaust port and repeating the test? That way you know for sure it is leaking. Which if it is your going to have to sort.

Time to take the head off, and check the valve stem tolerance, and if that's ok, lap the valves in,

If there is play in the stems, they need to be replaced, by an engine specialist and then lap the valves

Some people may be able to replace the guides at home, but ive never tried


steve

Putting a balloon over the exhaust port won’t show anything, it’s the inlet that’s leaking!
Probably best to check valve clearances, repeat test then if still the same take the head off , dismantle and check ALL valves, seats, and guides. Has it been modified for unleaded fuel? Valve seat recession can occur if the head doesn’t have hardened seats , could be a burnt or sticking valve, weak spring, or the valve has not been lapped? Modern valve seat and face cutting equipment is very accurate, some say there is no need to lap valves but at the very least I always check with engineers blue . At least it’s any easy engine to work on .

Thanks for the replies. I'll try to take the head off today and see if i can spot anything. I do have a new set of springs that came with my cam so they need to go on anyway.

Will report back.

An easy way of testing the valve sealing with the head off, is to turn the head so that either the exhaust or inlets holes are facing up, and pour petrol or diesel into all four ports, and the one leaking the most will empty in nano seconds
Then flip the head over, and do the other four ports the same way

I bet all four ports empty within 2-3 mins, max, xflows are not a very fine tuned piece of machinery, unless thousands are spent on them, and that's just a waste of money with some of the current spec engines you can buy

steve

Good idea. I'll do that while i wait for a new spring compressor to arrive. I had wanted to pour petrol into the valve bowl but because its a flat head i couldn't. Never occured to me to just pour it through the intake.
Thanks

quote:

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Originally posted by steve m
An easy way of testing the valve sealing with the head off, is to turn the head so that either the exhaust or inlets holes are facing up, and pour petrol or diesel into all four ports, and the one leaking the most will empty in nano seconds
Then flip the head over, and do the other four ports the same way

steve

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I couldn't hear or feel anything coming 'up'. So hope the guides are ok. Will be able to tell better once the valves are free from springs.
Thanks

I rebuilt an XE Coscast cylinderhead awhile ago and used a fluid to check the valve seating after I'd lapped them in

As said above you could use the same idea to check the seating in the first place although if your going to the trouble of taking the head off and change the springs you might aswell lap them in anyway

Also, with the head off, I always turned the engine over by hand, to put all the pistons level with each other
And fill each pot with 500mls of engine oil, the bowled pistons take a lot of it on a xflow

and just leave it like that for days, again it will gradually drop to the top of the pistons, due to the piston ring gaps
but again if one drops significantly then that's another problem to fix at the same time

This also gives the piston rings a good soaking, and free's up any stuck ones

steve

Oil is in the cylinders like you suggest while i get on with other things. Im assuming it'll take days to empty. Ive not noticed any draining yet... which i guess is good news.

Thanks