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Pertronix - Pros & Cons - Video & Pics

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Re: Petronix - Pros & Cons

I'd say a good head removel and carbon cleaning are in order... And I think the carbon buildup in that cylinder may be causeing the intermittent and low compression readings - could be carbon buildup holding a valve open sometimes, and allowing leakage. Then, you need to find and fix the cause of the excess carbon. Carb rebuild maybe?
 
Re: Petronix - Pros & Cons

"Forget the wires how bad is this"; absolutely horrible---Keoke--- /ubbthreads/images/graemlins/laugh.gif
 
Re: Petronix - Pros & Cons

[ QUOTE ]
I honestly didn't notice the numbers and didn't realize you were posting compression figures.

Obviously 0~110 is not good. It might just be a sticky valve. Or it's so burnt that it jams open sometimes?

You definately have a problem.

You might want to pull off the valve cover and see if you can see it sticking while someone cranks the engine.

[/ QUOTE ]
Such great compression in the other 3. Darn. While someone turns it over, what to I look for in a stuck valve? Could it be anything else? Imporoper valve adjustment? Cam lobes? Rings in #3? I am just throwing these out there now.

Once ya tell me what to do to check for stuck valve, i'll do it tonight.

The saga continues but I am still smiling /ubbthreads/images/graemlins/smile.gif
 
Re: Petronix - Pros & Cons

Valve cover off, car in gear 4th, push car a bit while watching #3, does the stem come all the way up? Check a lot, move the car a bit.
 
Re: Petronix - Pros & Cons

Easier way to tell: How many miles since the head was done? If you don't know - its time!
 
Re: Petronix - Pros & Cons

Actually the more I think about it... Even if you figure out if it is sticking or not it doesn't matter. Either way you need to pull that head. It's definitely a valve problem. The other numbers look really good so hopefully if you're lucky the rings on #3 are still good too.

You mentioned other stuff that's going through your mind right now:

Valves: almost certainly
Rings: probably OK (let's hope)
Cam Lobe: I really doubt it
 
Re: Petronix - Pros & Cons

I will check tonight. I should then also be able to check by turning the crank by hand with the vavle cover off and watching #3. If it does not come all the way up does that mean the there is crud built up around the seat? Said crud is preventing the valve from coming all the way up and not "seating" properly thereby not letting compression happen.

Not sure then the head was done but what does this entail & roughly what does it cost? How much besides removal can I do myself and what should I do to improve this?

I take it that this is not a piston ring problem.
 
Re: Petronix - Pros & Cons

Decoking a head is almost normal maintenance

the only way to tell if its a valve problem or ring problem is to do compression checks "wet" & "dry"...by that, I mean do a compression check right after pulling the spark plug....then, squirt some oil in the plug holes & pull another check...the "dry" will tell you if you have valve problems; the "wet" will tell you if you have ring problems.

However, I'm betting valves at a minimum...basically that's just removing the head & letting a machine shop do a good cleaning & 3-angle valve job...you'll need new seals at a minimum; seats or guides at most....but probably not either

I get mine done around here for somewhere near $125-$150 & that includes magnafluxing...seats cost me $12 each; installing/honing guides about the same.

You can have the head off on a Saturday morninig - they'll keep it in shop for several days to work into schedule - you can get it back on the next Saturday.

Unless the "might-as-well's" don't get you.
 
Re: Petronix - Pros & Cons

but since you're going from 0-100 on #3 the squirt trick isn't going to work for you until you can get consistent pressure in #3. That's why I said hopefully the rings are good. Unfortunately you might not really know until you fix the head and put it back on.

And what Tony quoted is about what I paid 15 years ago... He lives in a corner of the world where services seem to be significantly cheaper so I'd figure around 200 bucks wouldn't be that far off. /ubbthreads/images/graemlins/smile.gif
 
Re: Petronix - Pros & Cons

Not a difficult job at all, call your machine shop and ask what they charge. They for sure have a price list and will understand your problem.
 
Re: Petronix - Pros & Cons

[ QUOTE ]
He lives in a corner of the world where services seem to be significantly cheaper

[/ QUOTE ]

Jim - ain't that the truth! However, it might also have to do with the volume & longetivity of my work - once I find somebody good, I stay with them...& they reward me for it....Jack Laird just learned all about the cost of living here in north Alabama!
 
Re: Petronix - Pros & Cons

Hey Tony.

do you have em do the hardened valve seats for no-lead when you do it too?

I can't remember the exact terminology... Stellite? something like that.

This is one of the might-as-wells he should probably do since he's in there. Make it a leaded-gas free head. (I know - some of you have been using it for years without additives - but since you're in there anyway....)
 
Re: Petronix - Pros & Cons

[ QUOTE ]
do you have em do the hardened valve seats for no-lead when you do it too?

[/ QUOTE ]

Not unless the seats are bad....I've never had a problem with any MG head & unleaded gas....but I religiously put 93-octane in all my MG's.
 
Re: Petronix - Pros & Cons

I decided to not worry about the lead free gas and keep my eye out for a 12G206 or 12G295 head so I can do the works to it.
 
Re: Petronix - Pros & Cons

Well I guess tonight I am checking #3 wet as a starting point. If that is in conclusive, I'm pulling the head off right?

One should not drive for extended periods of time like this should they?

Is this something that can be blown out a cylinder or is that considered a bandaid and the problem lies deeper.

If you remember I had a lot of fuel problems which I think have been resloved. For the time I have run her, could it have caked this on or is this 39 years of slow decay?

"39 years of slow decay"
 
Re: Petronix - Pros & Cons

39 years of build up. Factory really suggested pulling head and decarbonizeing on a regular basis.
 
Re: Petronix - Pros & Cons

#3 wet is going to be inconclusive

You are going to need to pull the head. To do that you're going to need to pull off the valve cover (easy). See if anything looks goofy under there (it will be obvious). Then pull the head.

I wouldn't drive it myself. Once the valve train gets wonky it's possible to drop a valve or burn off a chunk or whatever and drop down and trash the piston and put in motion a chain of catastrophic events.

That being said I drove around for a good 3 months on 3 cylinders with a quarter-inch notch burnt out of a valve one time.... but I was young, dumb, broke, and didn't have any other transport.

a blown out ring on the #3 piston would give you consistently bad numbers

No telling if it was just old age or running it with mis-adjusted carbs. Doesn't really matter at this point.
 
Re: Petronix - Pros & Cons

Just to set things in motion, I emailed 3 members of my club for a machine shop recommendation. I'll most likely pull the head tonight & post pics. Oh boy. Fun, fun!
 
Re: Petronix - Pros & Cons

I'll have my vomit bag handy!
 
Re: Petronix - Pros & Cons

While you've got the head off, its not that hard to pull the pan from underneath, loosen the rods & push the pistons out through the top...then you can hone the cylinders, replace the rings & rod bearings...then you won't have to repull the head if there are ring problems.

Factory suggested replacing all bearings every 50,000 miles anyway.
 
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