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Loss of Power/Oil pressure when hot  Rating:  Rating
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 Posted: 12-12-2005 08:14 pm
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Joel
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I think I have most of the gremlins out of the ignition system. I have not driven the car in a while as I've been too busy to futz around w/ it. So, on Sunday I decided to go for a drive - lots of friends in town to pick me up, tow me, or just lend moral support if I broke down. . .

She ran like a champ. Better than ever. The new ignition bits seem to be coming together.

New problem, I had the fan disconnected. No big deal it's a cool 65 degrees here and as long as I was moving the temp stayed well below the middle of the guage. I would say it took 20 minutes or so for the guage to hit midpoint.

But, as the temp climbed my power disappeared and the oil pressure started to drop. I know it was temperature dependant because until the temp guage reached the middle she ran like a champ. At one point I got stuck in traffic and the guage crept just a wee bit past the center point - no where near 'hot' - the pressure dropped even futher and of course power went completely 'bye-bye'.

I reconnected the electric fan, drove slowly home and let everything cool down - again it never really got too hot but was running just above the center of the guage.

I started the car up this morning - oil pressure is back up to well over 50# at idle (800-1,000rpms).

Any ideas?

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 Posted: 12-13-2005 11:33 am
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Brett Gibson JH5 20497
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Joel, what wieght oil are you using, from my experience JH's like 20-50, and some loss at temp. is expected, 50 at idle is pretty much normal.

As for loss of power at temp. I assume your running Stromberg carbs, while you can faff about and dial in the temp compensator / by pass thingy's and all the rest, the best results I achieved was just blanking them off and setting the mixture after that, that is of course as long as the ignition is spot on.

Brett. 

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 Posted: 12-13-2005 02:32 pm
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Judson Manning
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Joel,

You are describing a common oil pressure issue, and Brett has some good ideas about the carbs.  If I had to bet, I'd say your oil pump rotors are worn.

The clearance between the lobes of the rotors should be 0.002"-0.006" (this is different than the pump-to-housing clearance, which is just as critical).  The pump will pump oil with as much as 0.012" clearance, just not as much volume. 

When cold, it's impossible to diagnose this problem.  Confusing issues is that it takes much longer for the oil to come up to temperature.

Once the oil heats up it naturally loses viscosity, and the pump basically cavitates and can't pump enough volume to keep the pressure up. 

Low pressure causes the oil to heat up more as there isn't enough of it to carry away the heat of the bearings.  In turn, this 'hotter' oil puts more load on the radiator, which is why your water temp may creep up 10-20^F.

Judson

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 Posted: 12-13-2005 04:36 pm
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Joel
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sitting in the pub last nite i discussed this problem w/ a motorhead acquaintance of mine. he agreed about the wear on the oil pump lobes. it seems he had the same kind of problem w/ a mechanical fuel pump.

i'm running 20-50. when all is well, at idle i have greater than 60#'s of oil pressure.

so - is the oil pump rebuildable? i do have a spare engine i just picked up so i guess i could take the oil pump off and take a look at it.

and it has been taking what i thought was an inordinate amount of time for the engine to reach operating temperature (or the middle of the gauge where it usually holds). but, i was running it pretty hard at about 1/4 gauge and she ran the best she's run since i've had her. when i hit 'normal' operating temp according to the guage(after 20 minutes or so of driving)everything started to go downhill.

regarding the carbs - i'm trying not to fart around w/ them yet. i think doing that is just opening up a can of worms. i have too many variables right now. the ignition is getting closer to right - and i don't want to be futzing w/ 17 things at once or i'll never get any of them right. when i get everything else in order - i have a set of dellorto 40's that i just had rebuilt, i figure i'll just swap the stombergs out.

maybe i'll just run it for 20 minutes, shut it down, have a coke and then start it up again. . .:-)

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 Posted: 12-13-2005 05:08 pm
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Jensen Healey
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No power when the temp rises? You're not going to lose that much power from a bad temp compensator. If you want to disable it just turn the spring over. It will just close more tightly as the temp rises.

Your hot oil pressure should be about 10lbs at idle and around 50lbs at 2500 rpm. If it's lower than that you should suspect the main bearings as well as the oil pump.

Check for a strong spark at high temp. I know you just fixed the ignition, but whenever I have a problem it is always the last thing I "fixed".

Kurt

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 Posted: 12-13-2005 05:24 pm
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Joel
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JH - thanks for the comments.

My only question is - if there is indeed a lack of spark at high temp - what would cause that? I agree that since this has been a big problem - it still could be. . . It was doing some flaky things before, like not firing on 2 cylinders when everything seemed to be fine. I replaced everything (dist,cap, rotor, coil, wires, plugs) and it still did the same thing. But, it just decided (after much fiddling) that it wanted to work again so all seemed well until now.

And if the bearings were bad - would the pressure change be temperature dependant?

I'll heat it up and test the spark. For such a simple ignition system this has been a pain. I recently changed out the distributor and replaced the electronic ignition with pertronix. When Pertronix comes out with their replacement distributor in 06 I think I'm going to jump on it. It's only going to be around 100 bucks (according to Delta). So it seems like the right way to go.

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 Posted: 12-13-2005 07:34 pm
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Judson Manning
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For some reason, JHs aren't very kind to oil pumps.  A used one is worth a try, but I'd suggest getting a new one.  I bought my lobes for $200/set from Delta, then heard prices around 60 pounds-sterling from someone on http://www.pistonheads.com.

Reading between the lines, what I'm sensing is that your car may have several small problems with it all combining to drive you insane.  With Winter approaching, it may be a good time to consider tearing it all down for a thorough inspection.

The important thing is YOU having fun with the car!

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 Posted: 12-15-2005 02:05 pm
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Harkes
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Hi Joel, I wish i could help you with your problems but i can't think of anything other than has already been said.. :(

I do think it's strange to loose power when engine is at normal operating temperatures.

I noticed you said something about NEW pertronix distributors.. Is pertronix making distributor for the JH? With AND with vacuum retard? What would make these better then the OEM? 

I have a new distributor with Pertronix ignitor II inside and an MSD6A unit. The new distributor always leaked oil and still might but i'll have to see once my engine starts running again.

I'm in for a new distributor if Pertronix makes one for dellorto's set up and internal weights set for a 2.2L  high compression engine.

good luck

erik

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 Posted: 12-16-2005 10:34 pm
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Joel
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I don't know the details but I do know that Pertronix is supposed to come out w/ an entire distributor for the 907. I don't know anything about whether it will have vacuum advance or not. Personally i was considering canning the vacuum advance anyway - as an experiment. Anyone else done this?

Joel

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 Posted: 12-16-2005 11:58 pm
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Jensen Healey
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First, it's vacuum retard not advance. To eliminate retarded advance go ahead and cap the vacuum tap on the manifold. The JH distributor has an aggressive curve with all of the advance by 2500 rpm. You can check with a tachometer and timing light.

Leakage can be cured by replacing the bushing at the base of the housing.

If you get a replacement 25D (MGB) distributor it will bolt right in but have a slow advance curve. I would guess Pertronix is not spending any time or money on development for the 9xx engines.

Most of this ground has been covered before. Read the posts from the old message board at http://www.jensenhealey.com/msgboard.mv Use the search function.

Kurt

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 Posted: 12-17-2005 01:11 am
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Joel
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Check the latest Delta specials sheet. They comment that a new distributor unit will be available after the 1st. I heard this from Pertronix as well when I called to ask them a question.

I'll let you know my 'scientific' comments after I block off the retarded advance.

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 Posted: 12-17-2005 02:13 pm
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Harkes
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thanks Joel, Kurt,

i'll keep an eye out for the new pertronix distributor and check specs as soon as they are there.

Erik

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 Posted: 12-17-2005 11:32 pm
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Joel
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Ok, maybe I should start a new thread w/ 'changing your oil pump' as the topic. Greg - feel free to move this if you deem it appropriate.

I took the oil pump off my 'spare' engine. I have not used a guage (mine isn't fine enough) to check the clearance. . .but it 'looks' ok. It is off a rebuilt engine that overheated and was taken apart again - so, I know I need to watch the oil pump. But, overall everything seems very tight. No play and very clean. I'm starting to wonder if PERHAPS some of my ignition problems on my car (not the spare motor) might stem from problems with the oil pump/distributor assembley. I'll keep ya posted as things progress. . .

I plan to take the oil pump housing off the car w/ the problem and compare the two. If they look similar (I'll use a guage on both of them) I'll buy new cogs and rebuild one of them. But, my only concern is that I have to take the cam belt off to do all of this. As long as I don't move anything all should be well but I'm still paranoid. And I'm thinking if I have to do this, I might as well replace the belt while I'm there.

So, just for fun, I Plan to move everything to #1 TDC. Then I should be able to take off the alternator and remove the timing belt. I will mark the position of the pulleys, etc, to make sure they don't move and then take off the oil pump housing.

Does this sound acceptable to all? I'm not a total hack but I think there's a lot of good experience here and I'm not shy to ask before I screw things up.

Also as far as measuring the clearance between the 'cogs of the rotors', I assume we are talking about the clearance between the inside rotor and the outer rotor at it's closest point (ie, when the cog rotates and 'closes' with the outer ring.

I suppose I could post pics but I think you'll all understand my point.

Using Greg's difficulty chart - I'm rating this at 2-3 glasses of wine. Of course, I'm drinking more just to keep it interesting.


Last edited on 12-17-2005 11:33 pm by Joel

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 Posted: 12-18-2005 02:57 am
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Mark Rosenbaum
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Mid-range on the JH temp gauge should occur at a coolant temp of about 190°F.  It is prudent to verify that your car's temp gauge works properly before assuming either that a temperature problem exists, or that your car is not overheating.

If the temp gauge is reading much less than it should, you could have fuel boiling in the carburetors.  Measure your fuel pressure at the carbs when the problem occurs, it should be 2.5 psi or so.  OEM fuel pumps sometimes quit once they get hot.  Install a new ignition condenser, these are sometimes heat sensitive.  Try a different coil and ballast resistor, these too can cause problems when hot.  Check your centrifugal advance when the problem occurs, sometimes the mechanism can stick when it warms up.

Normal oil pressure once everything warms up, using 20W50 oil, is a minimum of 5 psi at 1000 rpm idle, and 30 psi at 3000 rpm.  Full warmup takes about 15 minutes in very clement temperatures, and much longer if the outside air temperature is low.

You have to pull the crankshaft's fan belt pulley to slip a timing belt on or off the crankshaft gear.  It is highly prudent to do this first.  Next, set the crank about 45° before TDC, then mark the aligned teeth on the two timing gears with a permanent marker so you'll have a reference point in case either gear is disturbed during the belt change.  This moves all four pistons well down in their bores, so as long as you don't turn the crank you can't possibly have the valves impact the pistons.  During reassembly, static timing will be set after you return the crank to TDC and make sure cam timing is correct.

For the oil pump, there are three clearances: (a) the clearance between the flat face of each of the rotors and the cylindrical oil pump cavity, with the rotors in contact with the aux. housing; (b) the minimum clearance between lobes of the innter and outer rotors, and (c) the clearance between the outside of the outer rotor and the walls of the cylindrical cavity in the oil pump.

Of these, clearance (a) is the most important.  Its spec is 0.000,5" min, 0.001,5" max, and the pump WILL FAIL (lose the ability to prime itself) soon after this clearance reaches 0.004" or so.  In practice, this means the rotors protrude from the pump housing by the pump gasket thickness less the clearance spec.  You can determine this protrusion with a feeler gauge and a straight edge across the rotors.  ONLY Lotus' plastic gasket (also sold by Delta Motorsports) will work here.

It's my understanding that clearance (b) determines the pump's ability to produce oil flow.  Clearance (c) seems to affect the pump's peak pressure and isn't quite as important as (b).  Both of these can be 0.002" or 0.003" over spec without causing major problems.  Since pump rotors are very expensive, this is a good thing.

Somewhere in there you ought to discover clues to whatever ails your car.  That's usually the hard part.

Last edited on 12-18-2005 02:58 am by Mark Rosenbaum

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 Posted: 12-23-2005 11:37 pm
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Joel
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Ok, I'm back after a hiatus. No work done yet. 1st thing I want to do is get rid of the ballast resistor wire. It's in bad shape (cracked w/ wire exposed) at the coil so I figure that's the 1st place to start.

I have a wiring diagram. My diagram shows the wire going into some kind of a junction (w/ one off the starter, heat temp indicator and one more i can't remember off the top of my head). Where is that junction and what does it look like?

I assume it's under the hood but couldn't find it. I can't imagine why you would need this connection under the dash - but is it?

Would it be the brown,shiny coated wire under the dash? I'm just planning to run a straight wire - once I figure out which one it is.

Merry Christmas all!!

Cheers,

Last edited on 12-24-2005 01:04 am by Joel

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 Posted: 12-24-2005 08:25 pm
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Gary Martin JH 15371
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Joel,

The wiring connector you seek should be right under the power brake booster. There are two connectors there. One has four wires: ignition wire to balast resistor, wire for temp guage, wire to starter solinoid, and one to the alternator for the charge or ignition light. The other connector with the large brown wires are the main power wires to the fuse box. There are two other wires not in these connectors that run to the windshield washer motor.

The ingition wire is either a standard wire, white with a red stripe as I recall, or the Nichrome wire that is used on later cars that replaces the balast resistor. I'm not sure what color the Nichrome wire is. I beleive in either case this wire runs to the back of the tach under the dash. The other wire from the balast resistor to the starter provides full 12 volt power to balast resistor only while starter motor is engaged.  

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