Hey guys. Im still having trouble with my VC Valiant over heating at highway speeds only. Can anyone tell me what the timing should be for 1967 225 slant motor that is running on LPG ONLY??? I have the factory service manual here that says that normal setting is 5 degrees retarded??

Thanks in advance

There is an expert here, Frank, he may reply and have some suggestions.
Or you can slide on over to his propane forum and ask there. Many good guys over there well versed in LPG.

http://fuelsforum.rasoenterprises.com/viewforum.php?f=5

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Mattelderca
78 NYB (gone now), two S series, three old Snow Cruisers and a Doo.

The optimum LPG advance curve for each engine is different but a good starting point is the 14-14-14 rule:

• 14° initial advance
• 14° centrifugal advance (total mechanical advance of 28° all in by 2500 to 3000 RPM)
• 14° vacuum advance.

One of the members here (65CrewCabPW) also has a slant six running on LPG and is using the MegaJolt fully programmable ignition system. He has reduced his total "mechanical" advance to 22° @3000 RPM from 29° @ 3000 RPM at his last report.
Fuelsforum: Update on the truck

With LPG's high resistance to knock, advancing the timing to the point where there is pinging means that it is way over advanced. The object of optimizing timing is to have the combustion pressure peak occur in the ignition cycle where it can maximize the torque on the crankshaft at all times.

_________________
1965 Plymouth Barracuda,
225 engine, Quadrajet, HEI, Dutra Duals, 904 Torqueflite, 2.76:1 axle, Addco front bar
Rods & Relics - Fort Erie, ON / Collector Car Tech

Thanks Frank

That makes sense to me but i have no idea about adjusting the timing through the rev range???

Currently at idle the timing is at 2.5 advanced and the dizzy has a vacuum advance on the side of it but I have no idea how much effect that has on the timing.

Do I need to set so the timing is at about 14 degrees advanced at idle and then see how it goes? Maybe this is a job for a pro?

What do you reckon?

Thanks again

I would first check to see what timing is built into your distributor. You can mark your damper with paint and use your timing light to measure the advance at various RPMs. It doesn't make sense to arbitrarily increase your initial timing without knowing your total mechanical and vacuum advance because you could easily over-advance your timing.

You can do this by marking the arc length of each advance segment on paper and then marking it on your damper. A slant six damper is 7" in diameter and the formula for this length for angle A is:

length = 7" x [A/360] x pi

So for various degrees of advance on a 7" damper:

28° = 1.710" / 43.4 mm
30° = 1.833" / 46.5 mm
32° = 1.955" / 49.7 mm
42° = 2.566" / 65.2 mm
45° = 2.749" / 69.8 mm
55° = 3.360" / 85.3 mm

There are already several topics in this forum about recurving your mechanical and vacuum advance. See Distributor Advance Curve Adjusting Instructions.

If you're up for upgrading to a MegaJoltsystem, this will allow you to recurve your advance with a laptop computer.
http://www.slantsix.org/forum/viewtopic ... 364#368364
http://slantsix.org/forum/viewtopic.php?t=51567

_________________
1965 Plymouth Barracuda,
225 engine, Quadrajet, HEI, Dutra Duals, 904 Torqueflite, 2.76:1 axle, Addco front bar
Rods & Relics - Fort Erie, ON / Collector Car Tech

Thank you so much for the info Frank.

It looks like I might need to take the car to a professional to get the timing done but now at least I understand a bit better what might be going on.

Its very hard to find good help on these old girls locally so I am very glad to have found this forum.

Cheers again and I'll let you know how I go..

I used several pieces of paper cut to the above the lengths. I would line one side up with the TDC mark on the damper and use some paint to mark the other side. You could just mark the damper with 28° and 42° to see if you're in the ballpark and to see what RPM is required to reach them.

The cost of going to a professional can add up very fast so it doesn't hurt to be able to somethings yourself, especially when finding the optimums will involve much trial and error. In this case, I think there is a lot to be said for using the MegaJolt system.

_________________
1965 Plymouth Barracuda,
225 engine, Quadrajet, HEI, Dutra Duals, 904 Torqueflite, 2.76:1 axle, Addco front bar
Rods & Relics - Fort Erie, ON / Collector Car Tech

LOL. Yeah an electronic ignition does look pretty good. I just want to get it running right for now dont need it to be perfect or optimum performance. Just trying to sort out this overheating business. The timing is currently set on about 20-25 degrees so I think this is probably way to far BTC and hopefully why the car is overheating at highway speeds when the advance system is making the problem even worse.

If this isn't why the car is overheating then I will really be out of ideas!!!

If your initial timing is set to 20° BTDC at idle (or is it 2.5° BTDC?), adjusting it to the factory setting of 5° ATDC will probably be an improvement. Keep in mind that it is possible that the damper could have slipped so it would be good to verify that TDC on the damper is actually when #1 piston is at TDC.

http://slantsix.org/forum/viewtopic.php?p=349343#349343

Have you checked for other possibilities like a collapsing lower rad hose (due to no internal coil)?

_________________
1965 Plymouth Barracuda,
225 engine, Quadrajet, HEI, Dutra Duals, 904 Torqueflite, 2.76:1 axle, Addco front bar
Rods & Relics - Fort Erie, ON / Collector Car Tech

If so inclined, you can remove distributor, dig into it, read the number stamped on the back side of slotted mechanical advance weight’s retainer that also holds the rotor button when fully assembled. Whatever the number is, say 7 then double it making 14, which is the amount of mechanical advance that distributor allows.

Vacuum advance should not become active at idle, it also has a range of advance depending on which version you have, additionally the vacuum advance also has a vacuum level it activates at, and kick-in vacuum level can be fine-tuned as well.

The timing set points: base (no mechanical or vacuum advance at idle); mechanical (based on RPM), and vacuum (controlled by throttle opening and or load on engine over idle RPM) are additive. Base + Mechanical + Vacuum = Total advance.

Hopefully you have a 7 stamped on your mechanical advance slot, as that will make the 14/14/14 rule easy to meet. If you your mechanical advance slot is calibrated to a different degree of advance one will need to shorten slots or find a correct part. There is info here somewhere on how much to shorten slots to attain desired advance, and recurveing distributors to adjust how fast mechanical advance dials in.

I would not trust the garage guy down the street to recurve a distributor, his eyes will glaze over thinking you are a nut case, and fiddle around doing nothing but running up the bill. This is a race engine shop type of project, or one that you can easily do after a little reading here on the subject for the cost of a little rat tail file, someone brazing up the slots if needed, or purchasing a part from one on this site.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Thanks for that buddy support bud. I have just adjusted the timing to 14 degrees BTC at idle and the car still started and idled beautifully. however when I took it down the street it missed a bit at strange times like when the engine was decelerating or chugging along under very low load at low RPM.

I'm wondering now if there is an issue with one of the advances?

Hmmm this is getting interesting.

I hope I can resolve it myself. It is made all the more difficult by my complete lack of any knowledge watsoever of the LPG system.

I'll let you know how I go.

Thanks again.

Yeah Frank someone had informed me about the lower hose issue and surprise surprise when I checked there was no spring at all. I was hoping the new one (with spring) I fitted would fix the problem alas here we are...

I have also just now realised I have a leak of coolant coming from the top of the manifold gasket right at the back of the engine.... Maybe this is the problem lol.

Hoping its not the head gasket but from what I can see in the service manual this is the only way coolant can be coming out of there. Does that sound right?

I haven't seen a spring in a lower hose in years. They aren't really necessary. Think about it. The only time a lower hose would collapse, is if there is a restriction, on the "suction" side of the cooling system (clogged radiator).

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

I couldn't really see that the lower rad would be collapsing either but it would be easy enough to check once the engine was up to temperature. All he would have had to do was rev the engine up to the highway cruising RPM where his temperatures started to climb.

The overheating and the radiator sludge mentioned earlier seem to point to a head gasket issue.
Symptoms of a Blown Head Gasket

As for the coolant leak at the manifold, the holes for the manifold studs are tapped into water jacket. There should be a thread sealer on the threads to prevent coolant leaks. This leak should not cause your engine to run hot though.

_________________
1965 Plymouth Barracuda,
225 engine, Quadrajet, HEI, Dutra Duals, 904 Torqueflite, 2.76:1 axle, Addco front bar
Rods & Relics - Fort Erie, ON / Collector Car Tech

Previously mentioned radiator sludge seams to have completely dissapeared now. I think I may have overreacted to some residue I found after the radiator rebuild.

Bottom radiator hose has been replaced with a new item that did have a spring in it.

I have set timing to 14 degrees BTC at idle but it seams to have issues at weird times while running up the highway. I'm starting to think one of the advances isn't right.

But I still dont think I have resloved the overheating issue... Getting a bit out of ideas and ready to send it to an expensive expert....