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Augusto 09-21-2012 12:15 PM

please help me diagnostic this problem
 
yes Ford engine... :D

Inline six 300 CID

I installed this engine in a Granada, I already have several threads speaking of this swap, I love the way it came out, but the point here is this:

The engine runs great but when I let off the gas and the engine slows down to idle, it starts shaking and missing badly, if I don't give it a little gas it will stumble and die.

While it's aproaching idle I can hear the exhaust poping, (it only has a glasspack and the pipe is 2" first half and 2-1/2" the other half)

It behaves exactly like when you do a valve train adjustment on a SBC while running, once you tigthen the nut past zero lash and the engine starts shaking.

It makes me believe that the lifters are like "pumping up" while it runs at speed and they remain stretched when the engine slows down.

After something like 40 seconds of shaking, the popping noise goes away and the engine starts idling smoothly.

I'm pretty sure the valves are being kept slightly open while running, this is why it won't idle, but when the lifters bleed down the valves seat and seal and the engine idles smooth.

What do you guys think? am I correct?

could it be that maybe somebody shaved the head and the pushrods are now too long and the lifters are having trouble with this? or maybe the lifters are worn or stuck? (the engine sat in a corner for like 10 years)

I was thinking that shimming the rockers up a bit may fix this problem? I started a thread asking if this valvetrain could be converted to adjustable but didn't get much help there.

It has a brand new carburator ignition and distribuitor, so no tuning problem.

Please help me with this problem.

thanks,

F-BIRD'88 09-21-2012 12:30 PM

I would look at the vacuum advance to see if it is adding too much advance during deceleration (highest manifold vacuum).
In excess of 15deg. I would look at the carb. Float height, fuel pressure dirt in air bleeds.

Basic carb idle speed rpm. Does turning up the idle speed fix it?
Vacuum leaks.

LATECH 09-21-2012 03:19 PM

I would check the lift/cam. Sounds like a worn lobe.
Badly Worn valve guides can also be an issue on those.

Augusto 09-21-2012 03:33 PM

the carb is brand new, less than an hour working, fuel pressure is ok, filter is new.

it did the same with the old carb.

I have the static timing set at 5 degrees, used to have it at several places from 5 to 12, same thing. Pings with more than 5 degrees, ??? this is weird, it shouldn't ping should it?

does the same with the vaccum connected or disconnected, no difference, it's connected to a ported port anyway.

I have the idle set at 500 rpm, does the same with the idle up to 800, which is too high to engage the trans into drive.

No vaccum leaks, checked spraying starting fluid everywhere.

the vaccum reading at idle is very low 9-10 inches. I'm at 6.600 feet of altitude so I don't expect a 39 inch reading anyway, but this is too low, even gives me trouble with the transmission shifting too late.

I don't think it's a worn lobe because after a few seconds of rough idleing, it smooths out and runs very nice.

the valve guides are in pretty good shape, so are the seats, just lapped them.

thanks for helping. :thumbup:

LATECH 09-21-2012 06:19 PM

could be a dizzy/pickup coil problem.

cobalt327 09-21-2012 06:25 PM

Having inadequate valve spring pressure can cause this. They could be allowing the lifters to pump up.

Be sure to check the lifter preload and geometry. Being that the valve train is non adjustable, the push rod length is critical.

Changes to the following will effect the p-rod length requirement:

Camshaft base circle diameter
Pushrod length due to wear or replacement
Milling heads/block
Different thickness head gaskets
Valve seat height changes from seat replacement or from valve seat grinding/cutting done during valve jobs
Grinding the tip of the valve stem when doing a valve job or different length valves
Lifter pushrod seat height due to different manufacturer
Change in rocker arm type or design, or ratio

cobalt327 09-21-2012 06:37 PM

You should be able to use more than 8 degrees BTDC initial timing. It sounds like the mechanical advance may have too light springs or the vacuum advance is giving too much advance and or is deploying at too low of a vacuum signal.

timothale 09-21-2012 08:56 PM

vacuum restrictor ?
 
The manufacturers used a lot of gadgets in the 70's to get the cars to pas US emmision standards , solenoids, to restrict vacuum, ,a plastic disc type thing looks kind of like a mini fuel filter that slowed down the change in vacuum, I had a Maverick 6 that would actually speed up when you first took your foot off the gas then slowly slow engine rpm,

Augusto 09-21-2012 09:09 PM

Quote:

Originally Posted by LATECH (Post 1592728)
could be a dizzy/pickup coil problem.

nope, it's got an early points distribuitor.

I replaced the points and condenser by the way, didn't help :(

Augusto 09-21-2012 09:18 PM

Quote:

Originally Posted by cobalt327 (Post 1592730)
Having inadequate valve spring pressure can cause this. They could be allowing the lifters to pump up.

Be sure to check the lifter preload and geometry. Being that the valve train is non adjustable, the push rod length is critical.

Changes to the following will effect the p-rod length requirement:

Camshaft base circle diameter
Pushrod length due to wear or replacement
Milling heads/block
Different thickness head gaskets
Valve seat height changes from seat replacement or from valve seat grinding/cutting done during valve jobs
Grinding the tip of the valve stem when doing a valve job or different length valves
Lifter pushrod seat height due to different manufacturer
Change in rocker arm type or design, or ratio

springs..?? hmm maybe

now, since I live in a place where it's very hard to get parts for this engine, it really lures me the idea of converting the valvetrain to adjustable, I have a 250 I6 chevy engine that could donate the rockers, I understand that both chevy and ford use the same 1.6 ratio rockers, am I correct?

seems to me like installing some studs in place of the bolts will let me adjust the valvetrain, don't know if the head has push rod alignment guides.

any ideas?

Augusto 09-21-2012 09:20 PM

Quote:

Originally Posted by cobalt327 (Post 1592733)
You should be able to use more than 8 degrees BTDC initial timing. It sounds like the mechanical advance may have too light springs or the vacuum advance is giving too much advance and or is deploying at too low of a vacuum signal.

how much total advance can this engine run? or should run for best performance? and at how many rpm?

the distrubuitor I'm using is a Motorcraft points type (late sixties maybe) with dual pot vaccum advance, I have only the end fitting of the vaccum pot connected to ported vaccum, the other, the one closer to the distruibuitor body is left open to the atmosphere. There's nothing in the vaccum line, like restrictors delayers or something, just a straight hose from the carb to the pot.

it's not a race engine, it's a daily driver but having it performing well is really cool.

Augusto 09-21-2012 09:27 PM

Quote:

Originally Posted by timothale (Post 1592777)
The manufacturers used a lot of gadgets in the 70's to get the cars to pas US emmision standards , solenoids, to restrict vacuum, ,a plastic disc type thing looks kind of like a mini fuel filter that slowed down the change in vacuum, I had a Maverick 6 that would actually speed up when you first took your foot off the gas then slowly slow engine rpm,

this is a swaped in engine, I removed all the emissions stuff, there's a single, straight line from the carb to distribuitor.

we don't have any emissions tests over here :)

cobalt327 09-22-2012 07:56 PM

Quote:

Originally Posted by Augusto (Post 1592782)
how much total advance can this engine run? or should run for best performance? and at how many rpm?

the distrubuitor I'm using is a Motorcraft points type (late sixties maybe) with dual pot vaccum advance, I have only the end fitting of the vaccum pot connected to ported vaccum, the other, the one closer to the distruibuitor body is left open to the atmosphere. There's nothing in the vaccum line, like restrictors delayers or something, just a straight hose from the carb to the pot.

it's not a race engine, it's a daily driver but having it performing well is really cool.

I'm not that familiar w/using the Ford 300 in a performance application- not that there's anything at all w/doing so, so I'm at a loss for "hard numbers" for timing.

I'd set it up to give as good of vacuum at idle as the initial timing will allow, then bring in the mechanical as quickly and as much as the engine/fuel/vehicle combo will allow w/o detonation. Basically same as any engine would be tuned, w/o having any predetermined numbers to work from.

But I just feel certain that you can work out a curve that will allow more initial- and that's the key to getting more vacuum and better throttle response off idle.

Be sure the vacuum chamber that's being used is advancing the ignition. You might try dialing in the timing w/o the vacuum advance at first, then bring it online after the curve is dialed in.

Augusto 09-23-2012 10:14 PM

thanks, I'll try to solve the rough idling issue then i'll fiddle with the timing as you suggest, I might even try the pertronix electronic conversion kit, I feel kinda too old school using points.

Augusto 10-20-2012 03:03 PM

Hello my friends, this is an update.

I came to the conclusion that the valves were floating when the engine returned to idle, so I removed the rocker arms and it's pedestals and installed shims under them.

I added up to four 0.3mm shims and the engine run great, never missed a beat, but the valves made a bit of noise, so I removed one, for a total of 3 shims which is 0.9mm (0.035 in)

With this shims the engine runs quite well, not as smooth as with the 4 shims but the valves are quiet.

The problem is that this ford pedestals pair two valves so I can't adjust them individualy, I feel I should convert to a fully adjustable valvetrain.

What could be the cause of this? I doubt this engine had the head shaved, I talked to the previous owner who had it since new and he said he didn't touch the engine ever, I replaced the head gasket with a Victor unit, good brand name, I doubt they messed up, and I see the gasket has about the same thicknes as usual. Is ti possible for the lifters to break appart or loose the circlips or something else, that makes them stretch beyond their limits and keep my valves open?

BTW I installed a brand new Carb and electronic distribuitor, just to make sure this engine runs as economical and reliable as possible.

Please comment my friends.


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