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Old 11-13-2014, 11:36 AM   #1
Bob Johnson
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Default Engine melt down

Background:

Stock Model A engine added 5.5 Snyder's head. Used new silicone gasket. About 100 miles since head change.

Problem:

Engine was running strong. Touring at about 50 mph some smoke started coming out tail pipe. Started up a hill smoke increased. Pulled over engine running rough lots of oily smoke out rear and blow by coming out oil filler tube. Temperature gauge did not show high reading.

Dismantle Engine:

Cylinders were 0.100" over-bore. Crank measured 0.060" under. #4 piston had rings fused to piston. #4 cylinder walls had aluminum particle score marks. The exhaust valve for #4 cylinder was bend and the valve would not close. Head gasket looked OK. No apparent damage to head.

Question:

What are the possible reasons for the melt down ?

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Old 11-13-2014, 11:45 AM   #2
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Default Re: Engine melt down

Sounds like that one cylinder ran really hot. Could there be some slag or casting flash in the new head that would block water flow around that cylinder?
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Old 11-13-2014, 11:55 AM   #3
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Default Re: Engine melt down

Too tight of piston fit may be the cause, or it could be a build up of crud in the rear of the cooling chanber, as the rear sets lower than the front. It always seems to be #4 that locks up first. Preignition or advanced timing could also be the cause.
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Old 11-13-2014, 11:56 AM   #4
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Default Re: Engine melt down

I find it interesting that the exhaust valve was bent. How could it get bent and would a bent valve contribute to the melt down?
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Old 11-13-2014, 12:07 PM   #5
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Default Re: Engine melt down

Quote:
Originally Posted by Bob Johnson View Post
I find it interesting that the exhaust valve was bent. How could it get bent and would a bent valve contribute to the melt down?
I was also wondering about that. Is there any chance it got bent during head removal?
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Old 11-13-2014, 12:17 PM   #6
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The valve stem had a groove where the guide wore it down. This indicates that it was bent for some time.
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Old 11-13-2014, 12:22 PM   #7
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Default Re: Engine melt down

How many miles did the engine have before the Snyder head was installed?
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Old 11-13-2014, 12:28 PM   #8
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Default Re: Engine melt down

I suspect the damage to the valve occurred during the old head remove; not a uncommon problem when removing a head ; if a screwdriver or wedge is driven in too far on the valve side it will bend one or more valves and the valves must be checked.
Just my opinion !!!

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Old 11-13-2014, 12:33 PM   #9
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Default Re: Engine melt down

Not sure on mileage before head replacement. I was told that there were not many miles on the engine.

I am fairly certain that the valve was not bent during head removal. The wear on the valve stem was only on one side of the stem.


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Old 11-13-2014, 12:36 PM   #10
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Default Re: Engine melt down

3 & 4 run hotter than others=more expansion of piston

pistons set up with too little clearance=scored pistons and scored cyl walls 3, or 4, or both

see it all the time

no matter what anyone tells u, pistons must be clearanced at .0035

this is especially so if using old school long skirt pistons

but we use .0035 even on short skirt 283 style pistons

valve stem may have been slightly off even when new from the sounds of it
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Old 11-13-2014, 01:48 PM   #11
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Default Re: Engine melt down

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Originally Posted by tbirdtbird View Post
3 & 4 run hotter than others=more expansion of piston

pistons set up with too little clearance=scored pistons and scored cyl walls 3, or 4, or both

see it all the time

no matter what anyone tells u, pistons must be clearanced at .0035

this is especially so if using old school long skirt pistons

but we use .0035 even on short skirt 283 style pistons

valve stem may have been slightly off even when new from the sounds of it
Tbird, I have read and heard about that .0035 clearance for a couple years. The pistons I got from Snyder's specify .003, which is what my rebuilder used. But you worry me, so I have some questions: is this .0005 difference determined by the bore and honing process? I've got about 1500 miles on my rebuild. How soon after my rebuild should I expect problems? What should I do now before a problem arises? Should I tear it down for five ten-thousandths, and how would that diffence be corrected? Could it be done with the engine in the car?

In short, how serious is this at this point in my rebuild?
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Old 11-13-2014, 04:52 PM   #12
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Default Re: Engine melt down

hmmm.
If you truly have .003, you are farther ahead than most.

What is supposed to happen is that the machinist is supposed to bore to the specified dimension, for example 4.000 (this would be .125 over of course).
The pistons are supposed to arrive in the box at .0035 under. But they never do. Sometimes the piston dimensions are not the same amongst the 4 new ones you just bought.
So, you mic each piston, and if you need more clearance, then you use your hone to get there. This implies that you have an outside mic that will go to 4.000 and an inside mic set that will go to at least 4.000. If ya wanna build a motor ya gotta have the tools.

In short to do it right you have to mic everything, and not just shove the pistons in the holes without measuring, which is what we see all the time.

I have honed cyls while the engine and crank were still in the car but you have to take extraordinary steps to protect the crank and its journals; and you have to wash the cyls and block walls down very meticulously. A royal pain.

If it were me, I would remove the plugs, buy or borrow a bore scope, get a good look at the cyl walls. If they are not scored, then re-scope every 1000 miles or less.
Were your pistons old school long-skirt (prolly I am guessing). More risk if they were.
When tight clearances seem to show up is between 500-1500 miles.

Whatever you do, keep the radiator filled and do not allow the engine to overheat. Be sure the timing doesn't get retarded; a late motor will run hot as hell.

When you use the scope, and if there are no score marks, you will feel better; then just re-scope every so often.

Modern day clearances are in the neighborhood of .002, which is waaaay too little for an A. So you have to avoid modern day shops that do not speak Model A. Also, I have seen new A pistons come with a slip of paper which says to set them up at .0025. Sorry, this is wrong.

Good luck. Scope and get back to us
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Old 11-13-2014, 05:36 PM   #13
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Default Re: Engine melt down

no problem before changing head? could that exhaust valve be hitting the head for some reason,adjustable lifter no clearance at valve?
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Old 11-13-2014, 05:43 PM   #14
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Default Re: Engine melt down

You need one thousants clearance per inch of piston diameter, especially with soilid skirt pistons. An engine bored one hundred to one hundred and twenty five thousants would do better with four thousants clearance. As said the back two cylinders do run hotter, especially if the cylinders have been sleeved. Sleeved cylinders can't transfer the heat to the water jacket the same because the sleeve isn't actually part of the original cylinder block. I've had some to argue this and even sink to the childish level of name calling over this matter. Engines that have been sleeved back to standard size will always run hotter .
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Old 11-13-2014, 05:49 PM   #15
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Default Re: Engine melt down

Quote:
Originally Posted by rocket1 View Post
no problem before changing head? could that exhaust valve be hitting the head for some reason,adjustable lifter no clearance at valve?
One thing for sure, If it was running with a bent valve that wouldn't close completely it would have had a dead miss that would have been obvious at all times. A bent valve would cause the engine to only run on three cylinders but wouldn't likely cause overheating in itsself unless the engine was straining or lugging. I figure the over heating was caused by expansion of hot pistons that didn't have enough clearance.
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Old 11-13-2014, 07:43 PM   #16
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Default Re: Engine melt down

Here's a #4 that seized. I pulled this one from a 3000 mile engine a few years ago.

In this case the seized rings were the result of piston design. This import piston did not have a reduced land diameter and was intolerant to heat excursions that other pistons would survive.

There's always a lot of talk about #4 cylinder running hot, but one point is overlooked: If the cylinder (block) gets hot, the bore actually increases in size. For the piston to seize the piston itself must get proportionally hotter than normal. For this reason I believe it is not the direct result of the block around #4 running hotter.

Something is going on during the combustion process, specific to the rear cylinder, that causes overheated valves and a hot piston specific to the stock A engine.

High performance engines take advantage of resonance, the speed of pressure waves in air, to 'tune' intake and exhaust systems to enhance breathing at specific rpm's (frequency points) This can work against an engine, too.

In an 'A' there is an odd related phenomenon. The design of the split intake manifold and cumulative log-style exhaust in conjunction with the pressure wave pattern created by the firing order will cause the rear cylinder to run lean at specific rpm points. To my knowledge no one has ever explored this in depth. If #4 runs hot, it may very well be caused by too-lean running of that cylinder, not a water circulation problem.

I'd love to try changing the length of the two intake runner arms to an un-equal length, and baffling the #4 exhaust manifold port internally and see what happens on a test stand. Too many projects, too little time left.
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Old 11-13-2014, 08:40 PM   #17
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Default Re: Engine melt down

of course the bores will expand with too much heat. that is what bores do. everyone knows that.
But everyone also knows that aluminum expands more than steel degree for degree.
It is the expansion of the piston that is the culprit. If this were not the case the required clearance would be ZERO, think about it.

It is not complicated. we need not know any more physics than that.

I was taught years and years ago what Purdy just said: .001 per inch diameter. If the old timers knew this, why can't we?

By the time I am done honing, some clearances do come out at .004 instead of .0035. Big deal.

Agree totally with Purdy. And look at where the coolant intake is on the motor. Between cyls 2&3. And the pump sucks from there. So why in God's name is the same amount of coolant gonna magically bathe cyls 3&4 when it is all being sucked up front.

Buy a cheapo HF IR thermometer and shoot the sides of the cyls like we have and see the temp diff for yourself!!!! Get some simple instruments, watch, and learn. Listen to a guy like Purdy with 8 zillion miles under his belt on 6 diff. Model As for 50 years. Nah, what does a guy like that know anyway.

Users have 2 options and let's keep it simple:
1. set it up tight like a modern engine and have it score and seize and bring it to me for repair
2. set it at .0035-.004 and have a good strong motor. Seriously, you can't live with that much clearance? It will keep you up at night? WHY? Tell me what can go wrong with .0035-.004 clearance. I need to know

Listen again...we are trying to save you money and aggravation......any takers?

and the valve clearly wasn't straight when it was new; there is no other explanation....but that would have been hard to know at that point
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Last edited by tbirdtbird; 11-13-2014 at 08:48 PM.
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Old 11-13-2014, 08:59 PM   #18
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Default Re: Engine melt down

I had the same experience just a year ago. the #4 piston on a newly rebuilt engine dramatically melted while I was cruising at about 50. The other three were also on the way to melting. Fortunately no damage was done to rods, mains, and valves. I posted on fordbarn to see if others had experience the same. At the time nobody had. Several people suggested I didn't know how to drive a Model A.

Since then there have been several posts on fordbarn about engine failure with the #4 melting.

My failed engine was returned to the builder. It was re-bored and new pistons installed. it was never determined what caused the failure. The builder felt he had allowed adequate piston clearance. What stands out though is that a number of the major suppliers had recently started stocking pistons from Taiwan instead of from US mfg Silv-O-lite that they had been selling before. The Silv-O-lite's are more expensive. My engine had the Taiwan pistons in it from one of these suppliers.

When the engine was rebuilt I insisted on Silv-O-lites. The engine has been returned and has been in an engine test stand for the past several months and has about five hours on it at various rpm's. The test stand is instrumented with water temp. exhaust gas (EGT), tachometer, gauges, and a running time meter.

On the test stand at 2,000 RPM with the GAV open one turn the EGT is 800, with the GAV closed 900. In a discussion with Silv-O-lie they said aluminum melts at 1220, however, the piston normally does not see as high a heat as the EGT reading due to the fuel and air coming in on it.

The engine is performing well in the test stand. I can only surmise the failure was due to the quality of the pistons.

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Old 11-13-2014, 09:13 PM   #19
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Default Re: Engine melt down

Tom, you da man.
I would love to know the number associated with this statement:
"The builder felt he had allowed adequate piston clearance."

If you were talking about pinion preload you would want the exact number i think.

And
"Several people suggested I didn't know how to drive a Model A"
seriously? who needs opinions from them anyway.

And despite all I said above, I will vote down cheapo foreign parts any day of the week. You get what you pay for, someone once said.....
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Old 11-13-2014, 09:41 PM   #20
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Default Re: Engine melt down

Quote:
Originally Posted by purdy swoft View Post
you need one thousants clearance per inch of piston diameter, especially with soilid skirt pistons. An engine bored one hundred to one hundred and twenty five thousants would do better with four thousants clearance. As said the back two cylinders do run hotter, especially if the cylinders have been sleeved. Sleeved cylinders can't transfer the heat to the water jacket the same because the sleeve isn't actually part of the original cylinder block. I've had some to argue this and even sink to the childish level of name calling over this matter. Engines that have been sleeved back to standard size will always run hotter .
b.s.
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