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By-pass valve removal tip

Posted: Sun Apr 28, 2019 6:10 pm
by whesbrook
Here is a tip I discovered since owning my DB.
1. the famous stuck by-pass valve, the standard advice is to use a tapered wooden dowel which one sticks into the end of the valve and then pull it out, simples !!!!. NO
Where do you get this tapered dowel, I had a shot at making one which without a lath is nigh impossible,you can whittle for hours and then fail anyway, so the easy way out is a 8 mm plastic rawl plug, the sort that is used for heavy garden gates and a 75 mm long wood screw. Engage the screw into the end of the plug but first put a small washer onto the screw shank. Put the plug in the top of the stuck valve and screw in the screw to tighten the plug in the valve. Loop a string onto the screw under the washer which stops it coming off when you pull the valve out. If the valve is well stuck, and the plug pulls out, put it back in and tighten it more than the first time. the plug, being parallel, gets a far better grip of the inside of the valve than the tapered wooden rod does and works first or second time.
Valve cleaning is then done using 1000 grade emery paper soaked in diesel to aid the solution of the oil products that caused the sticking and lessen the chance of scoring the valve.
SIMPLES !!!!!

Re: By-pass valve removal tip

Posted: Sun Apr 28, 2019 6:28 pm
by ollek
I have made many wooden dowels using a sharp knife and trying the dowel in the valve and taking off small amounts of material from the dowel until it fits. You do not need a lath in order to make a working dowel. If someone wants to use something else, please do so, but a wooden dowel made to the correct shape and size works just fine.

Re: By-pass valve removal tip

Posted: Sun Apr 28, 2019 7:18 pm
by db2d
I would not advocate ‘ Emery Paper ‘ for use on these valves, but it is the owners decision.

Re: By-pass valve removal tip

Posted: Sun Apr 28, 2019 7:25 pm
by ollek
I have to add that there is no reason for shouting "pull it out, simples !!!!. NO". And as db2d said, do not use emery paper on these valves, it will ruin the precise fit between the valve plunger and the boring in the valve chest. Removing even a small amount of material from the valve plunger and/or the boring, will lre4sult in a gap between the two parts and oil leaking into the top part of the valve. This will in turn partly close the by-pass valve, resulting in so called ghost lift. This means that the hitch is contently lifting with a lower than the maximum pressure and this can not be repaired as the diameter of the valve plunger can not be increased.

Re: By-pass valve removal tip

Posted: Sun Apr 28, 2019 8:46 pm
by whesbrook
I thought this idea worth sharing but obviously not,
the emery papers exact title is "1000 grade wet and dry".
I'm sorry my language offends the senses, but that will not be happening again.

Re: By-pass valve removal tip

Posted: Sun Apr 28, 2019 10:10 pm
by philedge
If a dowel didnt work for you but a plastic plug and screw did, then your idea is definitely worth sharing. If it worked for you then theres every chance it will work for others.

The internet and its forums are for sharing info/ideas/veiws, a principle often overlooked. Keep posting if youve got anything to share:)

Re: By-pass valve removal tip

Posted: Sun Apr 28, 2019 10:36 pm
by db2d
Using the device described incurs the risk of cracking the valve. These valves were matched to the valve chest during assembly at the factory and are not available or interchangeable.

Re: By-pass valve removal tip

Posted: Mon Apr 29, 2019 12:45 am
by GeoffDEAL
Hi it was part of the first service on DB 1200 the valves were removed by service man and polished with fine wet and dry paper to remove any marks from the new valves slightly sticking i was told at the time, the tractor has had no valve problems to this day. I would think it would take a long time and lot of work to remove much with 1200 paper but there is finer 1500 or more it has been suggested fine Scotch Brite pads work but havnt used them myself. Whatever removes the stuck valves is necessary, there is a vidio of using an anchor bolt to remove a very stuck valve and it worked so plastic should be fine, tapered sticks to circlip pliers on normal valves, the main thing is to pack rags-foam -paper towels round the top of valve chest so you dont loose anything when removing the valves, i found paper towels as they are white and easy to pack around good and a suitable mirror makes under cab ones easier to see.

Re: By-pass valve removal tip

Posted: Mon Apr 29, 2019 2:08 pm
by whesbrook
the chances of cracking a valve with a plastic plug and wood screw hand tightened is pretty remote, these valves were made from fine grained steel case hardened so they could grind them to the tolerance needed to work in the chest without any seals, 3 thou if I remember correctly.

If anyone is about to replace a mudguard with a new one I may have something you need to watch for.

Re: By-pass valve removal tip

Posted: Mon Apr 29, 2019 6:07 pm
by db2d
I have seen a number of these valves broken during the last fifty odd years. If the owner is aware that they can break it is their decision on the removal method. I have also seen well meaning people advise putting the valves in a drill chuck to polish them using abrasive paper, and this is definitely a No No !

Re: By-pass valve removal tip

Posted: Tue Apr 30, 2019 3:32 am
by Gard
I think a quick light touch with 1000 grit wet or dry "sandpaper" is really more of a polishing step than sanding, it will remove small fractions of one thou (0.001") from steel. Removing even 0.0001" takes a lot of work with 1000 grit. With tight fitting parts like this I would be very concerned about cleaning any grit or lint from the parts before reassembly. If you can get it clean enough to move freely with solvents, cloth or perhaps brass brush that is probably the safer way to go.