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Old 12-09-2019, 05:06 PM   #1
SteveR.
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Default Replacing pistons

I had a piston come apart in my "A". No idea on the history of the engine or the piston source as I've only had it a couple of years. The pistons look very new, at least the parts in the bottom of the oil pan do.

I intend to replace it myself...what do I need to do to ensure I have the most reliable engine possible?

Any recommendations on a dial bore guage, or an appropriate way to accurately measure the cylinder bore?

Hone to .035 clearance between cylinder and piston (that distance split between the two sides)?

Anyone have tips on honing?

I'll get a scale and balance all rods and pistons.

I've done work on auto and aircraft engines before, but never honed cylinders.

I do have Les' book and will read before proceeding.
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Old 12-09-2019, 05:51 PM   #2
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Default Re: Replacing pistons

Quote:
Originally Posted by SteveR. View Post
I had a piston come apart in my "A". No idea on the history of the engine or the piston source as I've only had it a couple of years. The pistons look very new, at least the parts in the bottom of the oil pan do.

I intend to replace it myself...what do I need to do to ensure I have the most reliable engine possible?

Any recommendations on a dial bore guage, or an appropriate way to accurately measure the cylinder bore?

Hone to .035 clearance between cylinder and piston (that distance split between the two sides)?

Anyone have tips on honing?

I'll get a scale and balance all rods and pistons.

I've done work on auto and aircraft engines before, but never honed cylinders.

I do have Les' book and will read before proceeding.


Honing is quite basic for what you're doing. You merely need to break the gaze on the cylinder wall to allow new rings to seat. No need to resize the cylinder unless it's badly scored. Then a rebore (not rehone) is in order). The other pistons should have the oversize (if any) stamped on top. Just order a piston the same oversize.
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Old 12-09-2019, 07:38 PM   #3
nick c
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Default Re: Replacing pistons

The piston to bore clearance is .0035, never use a dingle berry hone, it will not show defects in the wall, infact it will cover them up, always use flat stone to hone, it will show all imperfections. Use a spray bottle with diesel fuel to coat walls.
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Old 12-09-2019, 07:48 PM   #4
Tom Endy
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Default Re: Replacing pistons

A couple years ago two of the better suppliers switched the pistons in their catalog from Silv-O-Lite to those made in China, and they are junk. Myself and three other local Model A-ers had them fail in the same manner. The number four piston virtually melted, number three was following down the same road. this was right after an overhaul. There was no indication in the catalog that they had changed the supplier. I spoke with one of the owners and he told me what they had done.

If you are planning to buy new pistons, my recommendation is you go on line and search for Silv-O-Lite. They have an on-line catalog and have a section on model A pistons with a full range of sizes. They are a US company with a long time excellent reputation. You can buy them direct.

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Old 12-09-2019, 09:10 PM   #5
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Default Re: Replacing pistons

Great information everyone, thank you.
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Old 12-10-2019, 11:00 AM   #6
katy
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Default Re: Replacing pistons

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I intend to replace it myself
If one failed, the others are probably not far behind. Replace them all while you're at it.
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Old 12-10-2019, 11:11 AM   #7
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Default Re: Replacing pistons

A piston clearance of 0.035" will give you excessive piston slap. Get the decimal point in the right place at 0.0035" . Next is what is the maximum allow piston clearance for a worn Model A cylinder? I am sure that SteveR. will need this information on his engine.
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Old 12-10-2019, 12:34 PM   #8
Jim Brierley
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Default Re: Replacing pistons

A rigid hone is best, they tend to straighten the bores. Clean cylinders and below them after honing, otherwise the grit will do serious damage to the engine. Change oil within 100 miles to insure all is clean.
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Old 12-10-2019, 07:16 PM   #9
Drive Shaft Dave
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Default Re: Replacing pistons

United Engine &Machine,Sil -Vo-Lite pistons,
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Old 12-11-2019, 04:34 PM   #10
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Default Re: Replacing pistons

Ring ridge reamer might be good to start with.

If not a big ridge, the hone might take care of it, otherwise you'll be there forever and increase the cylinder taper to boot.

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Old 12-12-2019, 05:38 PM   #11
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Default Re: Replacing pistons

OK. step 1). measure the cylinders (all) top and bottom to determine if/ how much taper - wear. A machinist needs to do the measuring and visual inspection. He will be able to tell if it needs to be bored and what size for a complete set of rings and pistons and silv-o -lite are super and USA made. If this is the route taken he will do it and you will have .003-.004" clearance as mentioned above. If you buy inside mics. and a new Sunnen hone you are in $ 1,000 or more and still have to learn how to use the mic.and the hone will break your arm. If it does not need bore and pistons have him measure, hone and supply the pistons. All of this is done with the engine stripped and on the bench. Then valve work & bottom end as needed lifters,guides, timing gears. Short cuts are the long way around. 2). Everyone needs a good machinist even if you have been one. You can't buy the tools and machines for one job. You'd have to sell your house. I appreciate your back ground and experience and you could replace a piston, good luck finding just one - oh the machinist might have one.

Last edited by 100IH; 12-12-2019 at 05:44 PM.
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Old 12-13-2019, 07:30 AM   #12
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Default Re: Replacing pistons

Wouldnt this work?

https://www.amazon.com/Engine-Cylind...xpY2s9dHJ1ZQ==
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Old 12-13-2019, 10:00 AM   #13
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Default Re: Replacing pistons

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Originally Posted by old31 View Post
Sorry, that is just as bad as the berry brush.
A good portable hone such as the Sunnen model has the stones and shoes held pretty rigid. This allows for the hone to cut the high spots and not follow the low spots.
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Old 12-15-2019, 11:13 AM   #14
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Default Re: Replacing pistons

Replace all 4, while the engine is opened up! If one went bad and they appear rather new, that is not a good sign! Not sure what brand to suggest but, others will!
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