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Valve work

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trebor09/06/2018 15:36:58
1939 forum posts
216 photos

Just working on this head and finding the valves letting compression go I tried gently valve grinding with fine paste then tried toothpaste and Autosol but looking at this there is not much contact area anyhow. It does not look like there is any valve angle cut from new, is this right ?



This was the worst, all the carbon as stuck down the shaft. Any tips greatly appreciated.

Jon - Laser Engines09/06/2018 16:25:09
5623 forum posts
271 photos

if that is an asp then that silver ring on the valve is likely to be a groove worn in the cheese...sorry, metal and if so then its finished and you need a new valve. Its a common problem. I recently rebuilt 4 52's for a friend and they all had worn valves. I gave them a little tickle with some wet/dry paper but not all could be saved

trebor09/06/2018 16:51:18
1939 forum posts
216 photos

Its my old OS 61 fs, that ring is where I cleaned up the carbon off the valve seat with toothpaste and Autosol. If you look at the valve insert in the head there is not much for the valve to seat on. It cannot have had any more contact area than that to start with, I bet there was less to start with.

Denis Watkins09/06/2018 17:19:07
4634 forum posts
129 photos

An unbroken thin shiny line, is all that is needed Trebor, for the whole circle

And good springs to make the seal of course

Edited By Denis Watkins on 09/06/2018 17:20:00

jrman09/06/2018 17:39:25
417 forum posts
3 photos

My understanding (on OS's at least) is that the valve seat has a sharp edge and is not chamfered like a car engines valve seat. Grinding does little to solve the leak.

trebor09/06/2018 18:51:50
1939 forum posts
216 photos

Well I had nothing to loose as its an old engine so I ground away and it has made a glorious improvement, the inlet has a thicker line than the exhaust now but there is compression yes Also the valves are still proud of the head so the valves are still quite thick at the edges.

Jon - Laser Engines09/06/2018 19:56:42
5623 forum posts
271 photos

Ahh fair enough

If in doubt, rebuild the engine and rev the snot out of it. That will sort out any slight leaks in very short order

Tim A09/06/2018 21:48:36
234 forum posts
13 photos

Back in the day when it was common to grind valves on auto engines we used to give the valves a tap with a ball pein hammer to help seat them after lapping in.

Jon - Laser Engines09/06/2018 23:48:37
5623 forum posts
271 photos

yup, I do this with the laser valves

trebor10/06/2018 08:09:08
1939 forum posts
216 photos

I must admit using the fine grinding paste was a bit too rough my favourite was the Autosul chrome cleaner. What do you use ?

onetenor10/06/2018 22:02:19
1901 forum posts

Remove the carbon on the stems by spinning in a drill and using a blade to scrape the carbon...... Works a treat.

Jon - Laser Engines10/06/2018 22:45:05
5623 forum posts
271 photos
Posted by trebor on 10/06/2018 08:09:08:

I must admit using the fine grinding paste was a bit too rough my favourite was the Autosul chrome cleaner. What do you use ?

I don't. I have a fine diamond lap and do each one by hand with some oil.

Wilco Wingco02/12/2019 10:15:30
246 forum posts
3 photos

I have just bought a used ASP 80 F.S. very cheap in a good airframe. It was cheap because the engine had no compression, when I removed the head I discovered that one of the valves was stuck open. Is there any way to free up the valve without removing the head or would it be better to strip the head and check out the valve seats and valves. How do I free the valve if I do strip the head?.surprise

Engine Doctor02/12/2019 11:09:22
2593 forum posts
40 photos

You could try squirting some Plus gas around the valve to get it moving .Cam followers are prone to getting stuck if the engine is poorly stored for a long time and will hold the valves open when the cam pushes them up and they stick. Agian a squirt of plus gas will usually free them with a little finger pressure . It would be wise though to strip off the head and remove valves to clean the stems and seats .Once the head is off remove valve collets in a big plastic bag . That way if you slip you will be able to find the collet.. To clean the valve stem and head I put it in an electric drill and use an old razor blade etc to remove any thick carbon then fine wet and dry paper to finish off . I use fine valve grinding paste thinned with either a drop of paraffin or thin oil to re-seat the valves. You can test the seat quickly by putting a few drops of thinners into the inlet and exhaust and check for leaks . As the valves or follower are are stuck I would also check the rest of the engine for any gumming or corrosion as this can Kill an otherwise good engine in seconds . A quick look in the cam box and in the back of the engine (take off the back-plate) and you will see if there is any corrosion to worry about . Its worth checking as the 80 is a powerful old lump and generally good runners ..

Edited By Engine Doctor on 02/12/2019 11:14:28

Wilco Wingco02/12/2019 11:50:06
246 forum posts
3 photos

Thanks Engine Doctor. The push rods and cam followers are all working fine its just the inlet valve that is stuck. The exhaust is moving fine, suspect its gummed up from old oil. The engine flew a couple of years ago but has been standing since. The top of the piston, viewed through the exhaust port, seems very shiny so I don't think the engine has seen much service. General condition seems good so I will try the Plus gas trick first, if that doesn't work a full head off "service" will

FlyinBrian02/12/2019 12:48:16
667 forum posts
4 photos

I had an SC 91 with a valve that used to stick every now and again. I just took off the rocker cover and gave it a push and pull and it would be fine until it had been stored for a few weeks.

Former Member02/12/2019 20:38:59
3577 forum posts

[This posting has been removed]

Don Fry02/12/2019 21:24:22
4557 forum posts
54 photos

Join the club. And why do they bury the screws under the rocker cover. One day, I'm going to have to slice it all open to extract the screws. Joy.

Wilco Wingco03/12/2019 17:15:31
246 forum posts
3 photos

OK guys. Cover off but I can't shift the bolt holding the rocker assembly onto the head. Looks like someone may have tried this in the past with a duff Alan key and damaged the hole?. I have just ordered a bolt extractor set off e-bay but as the smallest is 2.5 mm I don't hold out much hope. Engine Doc, any ideas as to how I can remove this bolt?. Tried WD 40 no luck. I could try heat but am loathed to damage the head as I don't know what sort of temperature to try and with a damaged Alan key hole it might not work.broken heart

Chris Walby03/12/2019 18:25:18
1326 forum posts
332 photos

WW, I don't think WD40 will touch it, perhaps more luck with Plusgas or some other penetrating fluid.

Somewhere else on another post someone mentioned a good way of getting these sort of screws out (might have been Jon - Laser Engines or the Engine Doc). Another with a better memory will enlighten us, but I think it was something like driving a slightly oversize Allen key (possibly imperial) into the existing screw head.

Edited By Chris Walby on 03/12/2019 18:26:01

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