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73 MG oil pressure decreases

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Ok the plot thickens, I removed the cap, spring and shuttle valve. And noticed the seat of the valve had a shinny mark on the seat only 3/4 the way around. Also the spring has been making contact with the side wall from bowing out and a section of the spring is super shinny. Which leads me to beleive the bowed spring is causing the valve to be cocked to one side. This would account for the partial seating marks and the spring wear on only one side. After mesuring the spring with my calipers, the spring lenth comes in a 2.84 inches. That is only 2 thousands below recommended spring length. But with the partial seating it might allow hot oil to bypass reducing pressure. The shuttle vavle also has evidence of scoring and loss of chrome plating in some areas. I will order a new valve spring and copper washers and see what happens. Better to eliminate the easy cheap stuff first.
In the mean time I will try what Bill said and drop a 1/2 ball bearing in the place of the valve and shim it and see what it does while waiting for parts.
Thanks Guys will keep you updated.
Dan
 
if you switch to a ball bearing, I always used 9/16" ball bearing, this also involves shortening the spring.
 
Well since I have a short spring I should be good LOL.
Here is some measurements I did with my caliper.

MGSpring.jpg


Notice the spring legnth seated, Ater measuring depths and and taking into account the resseses of the cap and valve, and measuring the hole depth, these are the figures I came up with. Now I just need to check my old spring lb resistance at that 2.137" against a new one and the I can figure out the legnth needed for a 9/16 ball and what the difference in lb resistance is. The 2.137 is the seated spring length by the way. So if a new one exerts 15lbs of force (Guessing) I can estimate the the force required by the addition of a 9/16 ball, and trim to length.
BTW the 2.86" is out of the Haynes book, if the spring is shorter than that it should be replaced.

Isn't math fun?

Thanks Hap,
Dan
 
Yes- I forgot to say that you should shorten the spring. I thought that it was a 1/2" ball but if Hap says that it is 9/16" then I will agree with him, it has been about 20 years since I did that to my Mini.
Bill
 
9/16 is correct, Hap sent me one long ago and it works just fine but you really need to take some off of the spring.
 
Ok here is what I did,
I could not find a 1/2" or 9/16" ball bearing today, the biggest they have is 7/16". Since my spring was under length by the book I took a 7/16" stainless steal bolt 1 1/2" long that had a head thickness of .165 and fit perfectly in the valve guide. I cut the treads off reducing it down to 3/4" long, then rounded the shaft end so it would not catch the spring. See diagram:

MGSpring2.jpg


I then placed the assembly back in the car, reinstalled the oil pressure line and distributer and fired her up. At 900rmp she maintained 70psi cold. I will run her tommarow and warm her up and see if the increased spring pressure has any effect hot.
Either way I ordered a new spring and valve so it will be here in two days.
More to come...
Thanks guys!
Dan
 
BTW all my "Diagrams" were done in Office PowerPoint :p
Dan
 
It's just nice to have all of those tools to make those kinds of measurements and do that kind of exact cutting. The rest of us need to make do with hacksaws, hand files, and if we're lucky a drill press. We're all jealous of the work we've seen you do. Sounds like you are on the right track. Good luck tomorrow. I'm hoping this fixes your problem. I know you want to go out and drive and not pull an engine.
 
You could not have encapsulated my sedements better if you tried. Hey BTW I am still waiting to break ground on my "Shed" hehehehe I decided to buy a 40' shipping container and bury it under the slab of the "Shed" to act as a storm shelter. Just have to explain to the wife what the ramp leading down to it is for. Hey there is enough room for everyone including the car :smile: hehehehe
I will try not to speak of all the tools :p
Dan
 
Well the results, good pressure 70psi cold at idle to start, at normal operating temp driving down the highway at 3500rpm was 40psi. When I turned off and started down thea side road the presure fluctuated with the rpm and settled at 25psi at 2500rpm. when I arrived at my destination at an idle it was back down to 10 psi. Also when I returned home (after setting 2 hours) it was back to 70psi at an idle, and the same when I got back home. I did notice that on arrival to the house the water temp was 1/8" past the normal mark.

Question: should I have the heater valve open, could this cause a higher water temp with it cloased?

I will wait for the new valve and spring to come in before I test it any further. Either way it will have a new valve and spring in the end. If that fails then I am pulling the engine this weekend and inspecting rod end and main bearings.
More to follow.
Dan
 
Oh boy. Somehow that just sounds like work.
 
Dang, Dan! You're sure jumping through all the appropriate hoops! Good luck on this one.
Regards temperature: if she's running up there in temperature, opening up the heater valve and turning the fan on will indeed add to the engine cooling and should lower the temp a bit.

Doug
 
jlaird said:
Oh boy. Somehow that just sounds like work.
Click to expand...
A little with an MG usally = Alot :smile:

twas_brillig said:
Dang, Dan! You're sure jumping through all the appropriate hoops! Good luck on this one.
Regards temperature: if she's running up there in temperature, opening up the heater valve and turning the fan on will indeed add to the engine cooling and should lower the temp a bit.

Doug
Click to expand...

Well got the spring and valve in from MM and here is the wierd thing the spring is .10" less (2.76") than what the book says the min length is suppose to be (2.86"). Hmmmmm since I was thinking it would have better tension than the other, I decided to throw it in. Well from cold at 900rpm we are sitting at 55psi, the pressure still faded as the temp rose on the water temp. So I still ended up with 20psi at 2.5k on the tach and 10 psi at idle.
Well I was pulling the engine and transmission anyway to fix the rear engine oil leak (Cherry picker and eng stand at the ready!). At least MM had a rear plate gasket in stock. I will try the putty idea Jack told me about on the bearings to find out the gaps, and measure the crank and throws just to see where I am at if (when) I have to order new bearings.
More to follow,
Dan
:shocked: Ahhhhhhhhh
 
While you've got it out, might as well...
 
Picked up plastigauge today, and will check the main and throws, I am getting faster it only took me 2 hours and 45 min to go from running to out!

05-01-09_1723.jpg


I love my cherry picker!
hehehehehe
Dan
 
Oh my, come on down I'll show you how WE do a Bugeye.
 
What was I too slow :p

Well you were right Jack, was the mains:

05-01-09_2214.jpg


.003 in with the plastigauge, guess I will be doing a full rebuild, hmmm have the crank turned or not. If no scoring what would you do?

Added:
Well I mic'd the crank dia. and got 1.9741, if the original dia. was 2.0005-2.0010 by the book then I am looking at .0264 then minus that by .001 that means I need .025 main bearings. My math right?

Well crap MM only has bearings in .010 increments, I guess it will be .030 and I will have to have the crank turned down to 1.969, that way I should have .001 clearance.

Dan
 
Check the manual--I'm going from memory, but I think it says you can go only 0.020 under without heat treating it. That's totally impractical, so if it needs to be ground a second time, you'll have to get a new crank. These show up on eBay regularly.

Something sounds wrong here--if it really is 1.974, you should have more than 6 mils of clearance, which is a disaster. If it doesn't show obvious wear & scoring, that could only have happened by the crank grinder screwing up big time--then the thing would have been bad since it was done, not a new problem showing up now.

The crank should be right on, or no more than a half mil or maybe a mil under, and the clearance pretty much comes out of the other tolerances; that is, the caps and bearings are sized so the clearances are in the specified 0.001-0.0025 range (sorry if these numbers are wrong; I'm not at home so I'm depending on my memory, always dangerous at my age).

So, check the diameter again. If it really is 1.974, I think it's time to start shopping for a new crank.
 
Something just doesn't seem right here. If you are .003 under (assuming that your crank was ground properly last time) then it was ground to .024 under which doesn't sound right. If I were you I would re-mike the bearings and verify that they ate a lot closer to a ".010" multiple under standard and put in new bearings without further grinding. I am betting that your bearings are a bit worn and that the crank is fine (of course this is assuming that the finish is not damaged at-all).
Bill
 
Sarastro said:
Check the manual--I'm going from memory, but I think it says you can go only 0.020 under without heat treating it. That's totally impractical, so if it needs to be ground a second time, you'll have to get a new crank. These show up on eBay regularly.

Something sounds wrong here--if it really is 1.974, you should have more than 6 mils of clearance, which is a disaster. If it doesn't show obvious wear & scoring, that could only have happened by the crank grinder screwing up big time--then the thing would have been bad since it was done, not a new problem showing up now.

The crank should be right on, or no more than a half mil or maybe a mil under, and the clearance pretty much comes out of the other tolerances; that is, the caps and bearings are sized so the clearances are in the specified 0.001-0.0025 range (sorry if these numbers are wrong; I'm not at home so I'm depending on my memory, always dangerous at my age).

So, check the diameter again. If it really is 1.974, I think it's time to start shopping for a new crank.
Click to expand...
Billm said:
Something just doesn't seem right here. If you are .003 under (assuming that your crank was ground properly last time) then it was ground to .024 under which doesn't sound right. If I were you I would re-mike the bearings and verify that they ate a lot closer to a ".010" multiple under standard and put in new bearings without further grinding. I am betting that your bearings are a bit worn and that the crank is fine (of course this is assuming that the finish is not damaged at-all).
Bill
Click to expand...


Thank you, both of you for prompting me to recheck. The fist time I used a micrometer and guess what, the locking ring was hitting the block causing a false reading. After using my dial caliper I could go flush with the block. This time I came out with 1.9809 which means you guys were right. The is no scorring on the crank it actually looks great. But the bearings are definantly show signs of wear (copper marks bleeding through). I think your right Bill I should be good with .020 bearing and not having it milled.

BTW I just measured the rod throws and the book says 1.6254-1.6259 I got 1.6049 if my measurments are right then I am looking at a differance of .0205, so I should be good with new .020 bearing for them as well. and the rod end bearing look better than the mains. I got .002 with the plastigauge on them.

Hows the math look?

Thanks again!
Dan
 
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