Author Topic: Valve Timing  (Read 9686 times)

cobbadog

  • Member
  • *
  • Posts: 3804
  • Buzacott Farm Pumper.
Valve Timing
« on: 20 January, 2021, 04:26:42 pm »
For ages I have had an issue with this engine not running correctly.It runs really rough.
History was when I bought the tractor many years ago the oil pressure was way too low running at 5psi at running temp. So an engine rebuild was done using parts from davidbrownparts in the UK who were fantastic to deal with.
Since this was the first tractor engine rebuild I took my time disassembling the engine and took particular interest in this part of the engine, valve timing. I noticed at the time before undoing anything here that with the timing mark on the flywheel in the centre of the inspection hole, piston at TDC, both valves fully closed and the distributor facing #1 position that the dots on the cam did not line up with the gear on the crankshaft. Now at this stage the engine was running well but lacked oil pressure and compression was down a bit so I made my own new marks by making it have double dots on the crankshaft and cam gear. However if you look closely at almost the 1 o'clock position you will see some original dots there.
From memory when I discovered this I think I posted it up here and again from memory I was advised that this gear was possibly from a diesel engine and is why those dots are where they are.
So after trying many things over time I have now dug deep into here to see what really is the problem. As you can see the double dots are lined up as I found them when I stripped it originally and now they are still in the same position. I have been told that my next step is to put the engine on TDC and check the position of the valve at #1 and #4. At TDC #1 both valves should be fully closed and #4 should both be rocking, meaning the valves should be half open and half shut.

Does this sound correct?
My intention next is to remove the cam gear and rotate the cam until I get both valves closed at #1 and both on the rock or rocking on #4. Any thoughts are appreciated.
Cheers Cobba
Cheers, John & Dee. Coopernook. NSW.

wee-allis

  • Member
  • *
  • Posts: 534
Re: Valve Timing
« Reply #1 on: 20 January, 2021, 08:58:34 pm »

Cobba,  with #1 piston at TDC, both #1 valves should be closed, with the correct tappet clearance and #4 exhaust valve almost closed and #4 inlet just about to open, ie "rocking. You can't improve on that for cam timing on s a David Brown or the majority of 4 cylinder engines, having a firing order of 1.4.3.2.

Personally, I doubt that your rough running is cam timing related. BUT I could be wrong. Been known to happen.

Steve.
If it's old, treat it like gold.
 38 Allis B,50 Morris Six,  Moruya, Sth coast NSW.

cobbadog

  • Member
  • *
  • Posts: 3804
  • Buzacott Farm Pumper.
Re: Valve Timing
« Reply #2 on: 20 January, 2021, 09:33:16 pm »
Hi Steve and thanks for the info.
Your explanation makes more sense than one that was given to me a while ago so I will now look closely at what is moving and at what time.
IT was explained to me that the valves on #4 would be half open and the other half closed and from what I saw today that is not the case but your explanation might be what I am looking at.
I have a short day tomorrow with work so will get back to it then.
Thank you.
Cheers, John & Dee. Coopernook. NSW.

cobbadog

  • Member
  • *
  • Posts: 3804
  • Buzacott Farm Pumper.
Re: Valve Timing
« Reply #3 on: 21 January, 2021, 04:35:15 pm »
Well the cam timing is as I put it together and exactly as described in the workshop manual, both key ways facing down to 6 o;clock. Re checked the tappet clearances and all were good except one was a bit loose but not now.
Time to clean up and reassemble and look more in depth elsewhere.
Cheers, John & Dee. Coopernook. NSW.

rustyengines

  • Member
  • *
  • Posts: 2777
  • Townsville North Queensland
    • Southern Cross Register
Re: Valve Timing
« Reply #4 on: 24 January, 2021, 10:35:25 am »
On most engines at top dead center both vales are just open (paper thickness) it is what is called vale overlap very common
Ian
Southern Cross Engines, Lawn Mowers and old tools * TOWNSVILLE

cobbadog

  • Member
  • *
  • Posts: 3804
  • Buzacott Farm Pumper.
Re: Valve Timing
« Reply #5 on: 24 January, 2021, 03:31:40 pm »
Gday IAn. I'm not following the comment. If the tappets are not touching the valves and have the correct clearance are you saying that the valves are slightly open on #1? If so wouldn't that loose compression?
Cheers, John & Dee. Coopernook. NSW.

rustyengines

  • Member
  • *
  • Posts: 2777
  • Townsville North Queensland
    • Southern Cross Register
Re: Valve Timing
« Reply #6 on: 24 January, 2021, 04:54:42 pm »
No the piston at top dear center the finish of the exhaust stroke

The exhaust valve about to close and the intake valve about to open this is where the rock should happen and tappets would just be touching

next 180 turn the inlet valve opens all but to end of stoke
next 180 turn compression stroke both valves closed
next 180 turn exhaust starts to open at bottom of stoke
next 180 piston at top as exhaust valve close and inlet opens

You only have check to this on number one piston
I think there is some confusion on what stoke I mentioned and you mentioned
Ian
Southern Cross Engines, Lawn Mowers and old tools * TOWNSVILLE

cobbadog

  • Member
  • *
  • Posts: 3804
  • Buzacott Farm Pumper.
Re: Valve Timing
« Reply #7 on: 24 January, 2021, 09:27:13 pm »
Thanks Ian, #4 was the one you meant.
Not sure when I can get back to this this week but will try again tomorrow if time .
Cheers, John & Dee. Coopernook. NSW.

cobbadog

  • Member
  • *
  • Posts: 3804
  • Buzacott Farm Pumper.
Re: Valve Timing
« Reply #8 on: 14 February, 2021, 04:16:46 pm »
Well finally I am happy with the valve timing as it was from when I assembled the engine all those years ago and found no teeth missing and the valves are all timed correctly.
Next is the dizzy. So now I found out that I have a 'ring in' dizzy model DY4A and not the proper DZ4A. The difference is in the shape of the body as far as looking at it but I dont know what else. With a new condensor and coil it made no difference with the running of the engine with misfiring and flat spot. So I looked closer and today a mate noticed an issue with the rotor button. I would guess I have the correct rotor button for a David Brown even with the correct direction of the arm on the button but it is not a good fit on the shaft of the dizzy. There is a groove in the shaft for the drive lug to fit into and the drive drive lug is not as wide as the groove so it can move forward or backward. The mechanical advance is in good working order and has been cleaned up since I took the picture of the insides there. So at the moment I have it all back in place and static timed with "M" on the flywheel (Magneto) and the points just cracking and this is 7' or 8' BTDC which is where it should be set.
I once again drained the fuel tank and will dig out my endoscope and look inside it for flakes of rust. I am still getting fine rust settling in the glass bowl so I want to check that out and establish a good fuel flow to the carby. I will even strip the fuel tap and look inside again.
Cheers, John & Dee. Coopernook. NSW.

oldgoat

  • Member
  • *
  • Posts: 80
Re: Valve Timing
« Reply #9 on: 14 February, 2021, 09:53:03 pm »
After you get it back together its probably time to borrow a timing light and check that the ignition timing isn't all over the place.

cobbadog

  • Member
  • *
  • Posts: 3804
  • Buzacott Farm Pumper.
Re: Valve Timing
« Reply #10 on: 15 February, 2021, 04:40:06 pm »
Yes, i have a timing light but I have to organise a battery pack to run it as the battery is on one side of the engine along with the dizzy and leads and the opening to shine the light into is way over the top of the engine and back at the bottom half of the bell housing. This is ok but I need to be quick because then the HT lead to the light has to sit on the exhaust manifold.

Some suggestions have been to use something similar to JB Weld and fill the gap on the shaft to centre the rotor. Getting this right could be a challenge if I go ahead with it as it could make the difference of a few degrees.
Cheers, John & Dee. Coopernook. NSW.

voljon

  • Member
  • *
  • Posts: 37
Re: Valve Timing
« Reply #11 on: 17 February, 2021, 08:36:27 pm »
john, I have found that the DY4A distributor was used on Wolseley and rovers from 1946 to 1948, so the shape of the rotor top could be different and the arm on your DB rotor is messing with the timing as well as the loose fit. I have not been able to get a photo of a DY4A
rotor yet. regards,john

cobbadog

  • Member
  • *
  • Posts: 3804
  • Buzacott Farm Pumper.
Re: Valve Timing
« Reply #12 on: 18 February, 2021, 03:54:07 pm »
Cheers John,
I spent a little time after lunch to double check the fuel tap and that was all good. So I fitted that rotor button after double checking the sizes with the digital calipers and they were the same size. So turned on the fuel and started it up and it had a bit of a miss happening but I ran it for a while to warm it up and found it still had a flat spot but could not adjust that out with the air mixture screw and the 'miss' kept on happening.
So off with the dizzy cap and ran the multimeter over the HT and coil leads and again all were at 0.001 on the meter except the coil lead which was 0.003 but after a clean up of the spring to the carbon brush it did come back to 0.001 so that was good.
Did another start up and got almighty back firing happening so I shut it down and walked before I got too pissed off.
Will try again soon to find out what has changed so much.
Cheers, John & Dee. Coopernook. NSW.

famous fitter

  • Member
  • *
  • Posts: 169
Re: Valve Timing
« Reply #13 on: 18 February, 2021, 09:00:25 pm »
Hi cobba.

Go out to the shed and start the tractor Tonight  , turn the shed lights off and look at the dizzy cap and leads In the dark . My guess is high humidity at your place today ??

See how you go.

Cheers Justin




allisb

  • Member
  • *
  • Posts: 430
Re: Valve Timing
« Reply #14 on: 19 February, 2021, 06:46:40 am »
Guys, this is a real long shot.
But I can remember the apprentice working on a grey Fergie once, he?d rebuilt the engine and it ran terribly. Particularly at low revs. The reason? Valve springs. They looked ok, and in all honesty the new ones didn?t really appear that different. But that was the reason. New springs cured it, (along with a lecture from the boss)
Like I say, a long shot. But just throwing in my $0.02c in.
I spend most of my pay on old tractors and engines, I tend to waste the rest