Loose valve collet.

[talisman]

Checked valve clearances on my Thornycroft 80D  [Mitsubishi K4D]. It appears the inlet on no7 has a loose collet. It is sitting almost level with the end of the valve. If i turn 7 to TDC can i push the spring down enough to replace it ? Really dont want to take the head off lol. I thought a simple piece of wood with a slot in the end to push on the spring retainer might do ? Advice please.

[Flyboy]

No, you risk dropping the valve into the cylinder. If you can rig something to hold the valve closed you may get away with it. Pushing down on the spring cap will cause the valve to contact the piston which may do damage.

[ditchcrawler]

25 minutes ago, Flyboy said:

No, you risk dropping the valve into the cylinder. If you can rig something to hold the valve closed you may get away with it. Pushing down on the spring cap will cause the valve to contact the piston which may do damage.

We use to feed compressed air into the cylinders to hold the valves up while changing valve springs when I worked Offshore, but that was using a compressor at about 100psi with an unlimited amount of air to keep them up

[RLWP]

1 hour ago, talisman said:

Checked valve clearances on my Thornycroft 80D  [Mitsubishi K4D]. It appears the inlet on no7 has a loose collet. It is sitting almost level with the end of the valve. If i turn 7 to TDC can i push the spring down enough to replace it ? Really dont want to take the head off lol. I thought a simple piece of wood with a slot in the end to push on the spring retainer might do ? Advice please.

Almost certainly. The clearance between the valve and piston on TDC is very small;, around 1/16"

You can check this out by putting the piston at TDC, then pushing the valve down, diesel springs are often reasonably light. If it touches the piston, you know your plan will work

Richard

Edited October 26, 2017 by RLWP

[Tony Brooks]

I agree with Richard, do the test he suggest but dropping the valve into the cylinder is just about impossible. I changed my valve stem oil seals that way on a direct injection engine that would probably have a slightly larger piston to head clearance than yours.

Only thing I would say is to insert "modern"  in the second paragraph after "valve down". They are not on older designs like the BMCs

[X Alan W]

If the piston on that cyl is turned to TDC there is no chance of the valve dropping into the cyl, as said the valve springs are not to strong so could probably be compressed, one thought is to check the collet groove on  the valve stem for wear /damage as well as the spring cap as they don't usually come out if all is in order & correctly fitted

[larryjc]

Used to do this on Rover V8 Engines.  Get piston at TDC and valve can only drop a tiny bit.  I used an old open eneded spanner with jaws the right size to straddle the collet and cut in half with a hole drilled in the end. With the rockers removed you can use one of the drilled holes that holds the rocker shaft. Put a rocker bolt through the hole in the spanner and then back in the head.  Screw down on the bolt and compress the valve spring.  Once made the tool can be used over again.  Never had any damage to pistons but if it looks like you have a stuck collet then give the valve head a gentle tap or seventeen to free it rather than forcing it down onto the piston.  Hopefully its the collet that's the issue not a worn valve 'cos then its head off time.

[talisman]

Thanks for all the replies. I had a look again this morning and must admit i bottled it lol , after a few abortive attempts. Just havent got the confidence i used to have i suppose. However a friend who runs a one man maintenance business was at the marina. He was going to do a little work for me anyway later so i asked his opinion. He offered to have a look so i returned to my boat and removed the deck board and rocker cover. He had a tool that anchored to the rocker shaft once the rocker arm was shifted out of the way. A little bit of pressure and hey ho it slipped back in. Must of taken him 1 minute lmao , and he made it look so simple. Im just relieved and can highly recommend Brendon Hossack of K & A Boat Repairs, good man. Now i have seen it done i will have more confidence should something similar ever happen.