piston rings and bearing shells

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Colin6224#2
Posts: 26
Joined: Mon Jul 01, 2019 1:43 pm
Location: Grampian Region

piston rings and bearing shells

Post by Colin6224#2 » Mon Feb 10, 2020 12:52 pm

Hi
I have a 990 Selectamatic 1973.
The engine works well enough for the age and hours worked, about 14K varied and often not that hard hours.
However I notice that the oil pressure takes about 6 seconds to switch out the light when the engine starts from cold.
Second the engine always smokes noticably.
The cylinder head was reground and new valves fitted a couple of years ago. Injectors refurbished.

Would it be possible to replace the crankshaft bearing shells from the bottom without re grinding the crankshaft. Not best practice I know but for an old tractor on light duties would that work.
Where do I get a gauge and adapters suitable for measuring the oil pressure.
Is it practical to replace the piston rings without reboring the block. Again not best practice but I could replace the rings myself without the cost of the rebore. My fear would be that the piston bore is now more oval than circular and the old rings are at least a match to that shape.
This is a small farm tractor on light duties but I would like to keep it working. There isn't really the budget available for big mechanical bills.

Colin

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db2d
Posts: 2278
Joined: Fri Feb 24, 2012 10:01 pm
Location: Monmouthshire

Re: piston rings and bearing shells

Post by db2d » Mon Feb 10, 2020 2:01 pm

It is not possible to change the crank main bearings without removing the engine. There is normally a slight delay for the oil to reach working pressure. If the engine is not consuming very much oil the piston rings are probably ok. Regarding black smoke, be certain that the air filtration and intake system are clear.
davidbrownparts.com have the necessary parts for connecting an oil pressure gauge. The pressure can be checked by substituting the electrical pressure switch for a gauge.

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rid54
Posts: 232
Joined: Mon Oct 13, 2014 8:20 am
Location: Vallentuna, Sweden

Re: piston rings and bearing shells

Post by rid54 » Mon Feb 10, 2020 4:44 pm

You seem to have decided to measure oil pressure, very good practice, I'd say. A pressure switch can have bad precision.

Lots of things, besides the bearings, can affect oil pressure. Wear in the pump, leaking overflow valve etc.

New rings and honing the bores could be a good thing,

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ollek
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Location: South West Finland

Re: piston rings and bearing shells

Post by ollek » Mon Feb 10, 2020 4:50 pm

The Operators Manual for the tractor asks for increasing the engine revs to 1000 r/min after the engine has started and then check to see if the engine oil pressure light has gone off. The low idle speed for the engine is 700 r/min (and must be no less) and it will take longer for the oil pressure to build up if the engine is on low idle right after stat up. Honing the bores and fitting new piston rings have no impact on the oil pressure. The reason for a smoky engine is often due to light operations for a long time. Try to put some load on the engine for some hours and see if the smoking is less after this. It is very unusual for the oil pump to be worn out or the pressure relief valve to be at fault in these engines.

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cobbadog
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Location: beautiful Coopernook NSW. near Taree. NSW. Australia

Re: piston rings and bearing shells

Post by cobbadog » Tue Feb 11, 2020 5:12 am

I had a similar problem with my engine but it was badly worn bearings and it would have fair oil pressure at start up but then drop as it got warm to running temps. So I pulled it out and rebuilt the lot.
If your pressure is still good once the engine is at running temps then it should be ok. Try some of the tractor supply places online here in Oz for an oil pressure gauge and connections I bought mine here and was not expensive and was a manual gauge not electric which meant running a small flexible tube from the engine to the gauge.
As suggested clean air filter is a must and then work the engine hard under load for a few hours to see if the black smoke clears, your injectors may be dirty. It wont hurt to put an injector cleaner through a tank of fuel to see if that helps as well.
Main bearing shells cannot be replaced unless the engine is out, only the big ends can be replaced with the engine in frame.

Colin6224#2
Posts: 26
Joined: Mon Jul 01, 2019 1:43 pm
Location: Grampian Region

Re: piston rings and bearing shells

Post by Colin6224#2 » Tue Feb 11, 2020 1:50 pm

Hi All
Thanks for the comments.
Pressure Gauge is a good next step. See where that leads.

As for replacing the crankshaft bearings, your replies are pretty much as I had expected. I'm not to keen on spending to much money on the engine because the gearbox has a problem in second gear where it sometimes jumps out. Wear pads have fallen out.

Air cleaner is the oil bath type and has been cleaned quite recently.

I do try and give it some hard work but with (a) I don't have that much heavy gear and (b) I suspect that second gear wouldn't last that long if it pulled a plough or cultivator.

Time will tell.

Thanks

Colin

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bedwards1966
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Joined: Sun Mar 07, 2010 10:36 pm
Location: North Yorkshire

Re: piston rings and bearing shells

Post by bedwards1966 » Thu Feb 13, 2020 9:19 pm

I've a DB engine that takes a good 6 seconds to build oil pressure, but the pressure it has is good and it does not concern me.

Putting a pressure gauge on your engine to see what the pressure is is the first thing to do, if it has good pressure when hot then I'd not be worried.
If the pressure is on the low side it might be possible to replace the big end bearings to help a bit, but you wouldn't know how the crank was until you got it open.

Does the tractor have enough power for the work you need it to do? And does it burn too much oil?

Putting new piston rings in is sometimes possible, but if there's a wear ridge this may need removing otherwise the top ring can get broken and the cylinders would want honing to remove the glaze. Obviously there's a point at which if there's too much wear it would be a bad idea, and it's always considered a bit of a bodge but it can be useful at times. If the tractor is doing what you need and isn't burning too much oil I'd probably leave it alone.

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cobbadog
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Location: beautiful Coopernook NSW. near Taree. NSW. Australia

Re: piston rings and bearing shells

Post by cobbadog » Fri Feb 14, 2020 11:06 am

If you have good pressure when at running temps then all is good. I tried adjusting the pressure relief valve on the oil pump to improve my pressure and it did but only when cold. Once hot it dropped way too low because of the worn bearings and crankshaft.
It will be interesting as to what pressure you actually have, let us know.

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rid54
Posts: 232
Joined: Mon Oct 13, 2014 8:20 am
Location: Vallentuna, Sweden

Re: piston rings and bearing shells

Post by rid54 » Fri Feb 14, 2020 9:10 pm

I realise that replacing piston rings do not have anything to do with low oil pressure, but the thread owner mentioned it as a particular question. Honing the cylinders and attaching new piston rings will in many cases revive a tired engine. A wear ridge in the bore must be machined away, or special top rings with special profile should be used (if provided for this engine).

The oil pressure relief valve normally operates only when the oil pressure is very high, as when the oil/engine is not warmed up. However, if the spring is bad/cracked or the valve ball is obstructed and cannot close properly, oil pressure may become low due to oil leaking through the relief valve even if it is not "opened" because of high oil pressure. The principle is to investigate the components that are more easily got at first, before dismantling the engine.

Colin6224#2
Posts: 26
Joined: Mon Jul 01, 2019 1:43 pm
Location: Grampian Region

Re: piston rings and bearing shells

Post by Colin6224#2 » Wed Feb 19, 2020 8:36 pm

Hi
Next step is to find and fit the pressure gauge. Davidbrownparts.com couldn't supply the parts, they only supply standard parts and the add on gauge was never a standard fit.
So what have others done. I wanted something mounted onto the engine block so that I could remove the dash to do other work without having to disconnect and reconnect the gauge every time I need to work on or rather under the dash.

Thanks for your ideas.

Colin

philedge
Posts: 368
Joined: Sun Dec 03, 2006 11:27 am
Location: Chester UK

Re: piston rings and bearing shells

Post by philedge » Thu Feb 20, 2020 7:15 am

If you search ebay for "1/8 bsp pressure gauge" theres plenty of options for a gauge to fit in place of the pressure switch to see where your pressure lies.
'66 880 Selectamatic rat.

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manxmac
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Location: United Kingdom I.O.M.

Re: piston rings and bearing shells

Post by manxmac » Thu Feb 20, 2020 9:17 am

I converted my Q cab 990 to a liquid type oil pressure gauge some years ago with good results and greater peace of mind. I basically went on E Bay and if memory serves me right most of the bits were from a modification kit for a Mini Cooper. The original fitting in the block is replaced with a T fitting so you get oil flow to the warning light and also to the oil pressure gauge. I had the dash off at the time and cut another hole in the dash for the Mini oil gauge which matches the DB gauges quite well. The gauge comes with a length of nylon pipe and fittings.

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cobbadog
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Joined: Tue Oct 11, 2011 6:18 am
Location: beautiful Coopernook NSW. near Taree. NSW. Australia

Re: piston rings and bearing shells

Post by cobbadog » Thu Feb 20, 2020 10:15 am

I bought my oil pressure gauge online through a tractor parts supplier in Qld plus there are plenty of choices online and as stated buy the 1/8" BSP fitting and gauge and your good. As for placement of the gauge it can still go into the dash and if you need to remove the dash it is not an issue to unscrew the oil line to the gauge, just cover the end of the line and back of the gauge to keep any dirt out. Yes you will have a small air lock in the line but the gauge will still work or it it bothers you you can crank the engine over but not start it with the oil line loosely connected and oil will bleed out then tighten the nut.

Gard
Posts: 322
Joined: Sun Apr 06, 2008 2:25 pm
Location: Fairfax Vermont USA

Re: piston rings and bearing shells

Post by Gard » Thu Feb 20, 2020 4:17 pm

My local auto parts store has gauges for both oil pressure and water temperature (with sender). They have worked well for me. These were reasonably priced and came with a handful of adapters. If I was going to do it again I might look for something designed to be used in exposed areas, I think a little water gets into them when it rains. Not a big deal for me so far as the tractors are kept under cover.

ScottUSA
Posts: 70
Joined: Mon Mar 26, 2018 1:59 pm
Location: North Carolina

Re: piston rings and bearing shells

Post by ScottUSA » Thu Feb 20, 2020 6:03 pm

Slow to-build oil pressure at start might be the oil filter. I have an 885 with the oil filter in a can/housing, the 990 may be different. Someone had incorrectly assembled the various bits that seal the filter to the bypass and the through bolt. The result was oil in the filter house draining back into the crankcase. Oil pressure was slow to build because the housing had to be refilled before the light will go off.

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