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Twin "Z's" in a 1725

P. Scofield

P. Scofield

Bronze Level Sponsor
I have moved from 5000 feet to 800 and want to check and tune my twin Z's for this level. (basically, going to start driving my car).

The workshop manual gives data for main-jets for different altitudes, but it got me to thinking about stock engine CC's compared to what I am running, a 1725 bored 30 over.

So what allowance should I make? Or does this matter?

Thanks for the input,
Paul
 
R

RootesRacer

Donation Time
The stock jetted (for 1592) zenith will work with the 1725, though the venturi is a little small for the added displacement of the 1725 engine.

The jetting that is in your carbs is very likley the low altitude jetting, since unless the vehicle was sold at above 6000 ft, how it came from rootes is probably how it got sold.

I have ran the stock jetted zeniths on a stock 1725 and it ran quite well, producing more power and a nicer growl than the CD150s.

HTH
 
P. Scofield

P. Scofield

Bronze Level Sponsor
RootesRacer said:
The jetting that is in your carbs is very likley the low altitude jetting, since unless the vehicle was sold at above 6000 ft, how it came from rootes is probably how it got sold.
HTH
Click to expand...

I bought the car in Pueblo CO and I think it was sold there or in CO or NM at one time. I will take the jets out and see what they are stamped as I have no idea what I have.

P
 
P. Scofield

P. Scofield

Bronze Level Sponsor
How do I test or know if my Oil PR Valve is operationg correctly. I have herd some talk about low oil preasure readings because this valve is not working good.

Does Rick sell them?
Pauk
 
puff4

puff4

Platinum Level Sponsor
P. Scofield said:
How do I test or know if my Oil PR Valve is operating correctly. I have heard some talk about low oil pressure readings because this valve is not working good.

Does Rick sell them?
Pauk
Click to expand...

No, they are NLA at this point. They are known for sticking from time to time, but I wouldn't say it's an overwhelmingly common problem... low oil pressure is usually due to other problems like worn bearings or a faulty/missing timing chain jet. However if you feel the valve may be an issue you can either remove, clean and check your current valve, or you can go the extra step to make it adjustable.

For instructions on modification of the pressure relief valve, click below.

http://www.team.net/www/rootes/sunbeam/alpine/mk1-5/techtips/prvalve.html

If I recall correctly, the Series IV valve has a spring pressure that releases the valve at 40 lbs. psi, whereas the Series V bumped up the spring to provide 45 lbs. psi.
 
Paul N.

Paul N.

Donation Time
The usual reason the oil pressure relief valve causes low oil pressure is that after high mileages a curved ridge wears on the piston and it latches in the side hole. Forget about making it adjustable, just take a sharp implement and rotate the piston so that the wear ridge and the hole no longer line up.

I'm the only person I've ever heard of who's had the opposite happen and had an oil pressure relief valve stick closed and I got 90psi on a Series V with over 150,000 miles on!!!
 
P. Scofield

P. Scofield

Bronze Level Sponsor
I'm just now driving my car after finishing it 6+ years ago. Working some bugs out. My engine is new and only runs about 30-35lbs. I can't believe it's anything other than the valve being too open.

Paul
 
R

RootesRacer

Donation Time
There are several designs of OPR valves and even variation in pressures from valve to valve.

If the valve isnt sticking open (0 psi at idle) and the regulated pressure doesnt go up much at higher revs then the valve is working fine.

35psi is normal for the earlier valves, 45 normal for the later valves.

I wouldnt worry about 35psi provided you arent revving the hell out of the motor and the idle pressure is fine.
 
T

Tom H

Platinum Level Sponsor
Paul S. I for one think the OPR valve is a larger problem than most think. On my 7500 mile trip in Sept 2011, I had to pull it and clean it about every 1000 miles. Even after I swapped valves with Tracy in Seattle I still had problems.

I don't think it even requires the valve to be worn to where it has a "ridge" in it to stick. I think all it takes is a little bit of dirt, or maybe it's slight grains of worn metal. I know the OPV valve stuck partway open at least 5 times on my trip. At first when I would pull it and look at it, it would unstick before I could pull it out. But at least 2 times, I pulled it quickly enough and before the car cooled off much and I was able to SEE it stuck. See attached photo for proof. Each time I would exercise the plunger, pushing it in with a pencil and each time it would feel sticky on first push and then would feel fine. I would then clean it, and put it back in and all would be fine for the next 700-1200 miles. Then I'd notice a very low (near zero) OP while idleing. One additional thing I have learned about Oil Pressure is that oil viscosity has a temperature hysteresis effect. If the car gets very hot, like when idleing in trafiic, the oil gets thinner, of course, but then, even after it comes back to normal temp, the oil is still thinner than before it overheated. After the car is off and significantly cooled down, the normal viscosity, at normal operating temp, returns. I have learned to seperate these effects and I can spot when the OPV is sticking.

It's pretty easy to pull. (I can do it blindfolded!) Just takes a 13/16" socket to unscrew from the filter housing. Very little oil drips out- (Engine not running !).

Tom

View attachment 4140
 
Last edited:
RootesRooter

RootesRooter

Donation Time
P. Scofield said:
I'm just now driving my car after finishing it 6+ years ago. Working some bugs out. My engine is new and only runs about 30-35lbs. I can't believe it's anything other than the valve being too open.

Paul
Click to expand...

So these are the first miles on the rebuild, right?

There's always a chance the machine shop screwed up on the journal grinding. I bot such an Alpine once; the journals had been ground about 4 thou too much. Ran 25 hot at speed with a slight knock.

We've also read here recently of incorrectly sized replacement bearings.

In my experience a malfunctioning PRV will usually stick open far enough that the engine can't maintain more than 20psi at speed. Turn the engine off and start it up a little while later and its back to 40psi - for a few minutes.

Also try hooking up a spare oil pressure guage.
 
P. Scofield

P. Scofield

Bronze Level Sponsor
Well, by the sounds of things (and thanks for all the input) I probably don't have a problem but I will check it out. I will note the preasure a little closer next time I run the engine but I think I'm running a VERY cosistent 35lbs, Idle or rev. It goes up slightly when I run higher RPM's but not much.
Runs about 40 when bone cold until warm and then drops slightly.

I am on my first pan of oil still with straight 30 wieght.



P
 
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