PISTON HELP!!!

[Jonah D'Avella]

I got a new high compression head, and when I put it on without a gasket, the pistons hit the head, are my pistons taller than stock or something? I thought they looked normal. They lift the head about a eight of an inch.

[Jonah D'Avella]

Comparing the pistons to an old one i have, it looks like the taper extends a bit more than on the old one. could they be high compression pistons?

[Kerry]

If a Z head, then it is not unusual for the piston to hit, but you will not be able to remove 1/8" in the combustion chamber to compensate, that would be far too much.

[Jonah D'Avella]

Pics of piston

[Jonah D'Avella]

They don’t seem like the normal domed top high compression pistons, what could be wrong?

[Moxie26]

High compression Pistons will work with the standard Ford cylinder head. If you're going to use a high compression cylinder head, you must use standard Pistons .

[Jonah D'Avella]

are these high compression pistons?

[speedytinc]

Are you fitting a Z head? Confess!
Combustion chambers are all over the place, at least the 2 I installed & talking to others. This was years ago.
They required a complete re- machining to get even.
Wouldnt they run rough with varying compression??

No such problem with a Prus head. Installed 3 of them.

The pistons you are using dont look out of the norm, in fact they dont look to be all the way on TDC.
Your pistons are not the profile of hi compression units. HC pistons have a full spherical top.

As an aside. Still running some 2 piece valves?

[speedytinc]

are these high compression pistons?

No.

[DanTreace]

Clean all the carbon off piston tops and cylinder face. Then put some dye , Prussian blue on the inner chambers and fit head loose with couple of head bolts. Crank over, then check where piston tops hit the head chamber. Remove by grinding away alum surface in the head until no contact. Usually only a couple of pistons strike, as the Z head is as cast and some chambers are more shallow.

[DanTreace]

Clean all the carbon off piston tops and cylinder face. Then put some dye , Prussian blue on the inner chambers and fit head loose with couple of head bolts. Crank over, then check where piston tops hit the head chamber. Remove by grinding away alum surface in the head until no contact. Usually only a couple of pistons strike, as the Z head is as cast and some chambers are more shallow.


IMG_1204.jpeg

[Norman Kling]

They look to be a bit high from your pictures. Also if the cylinders have been bored oversize, the piston might be hitting at the edge. Try using some Prussion Blue on them and you will see where the blue is hitting the head and be able to judge for yourself. Sometimes grinding a bit off the head at those points will cure it. If they are high compression pistons, you need to use a standard head likewise with high compression head you need standard pistons, but do not use both high compression pistons and head. Also if either the block or head have been re-surfaced, too much might have been ground off. Dan has it right on. He was typing his answer while I was doing mine!
Norm

[Jonah D'Avella]

ok. any good ways to clean the carbon off? and yes, it is a z head, I just cant afford a pruss head at the moment.

[speedytinc]

ok. any good ways to clean the carbon off? and yes, it is a z head, I just cant afford a pruss head at the moment.

I use a good/sharp quality wood chisel. Cover where you dont want the loose stuff to go. I finish with a cup wire wheel.

Back in the day when there were no other choices, My chums & I concluded the Z head was the greatest thing since sliced bread..................If you are a machinist. You will need to remachine ALL the combustion chambers( At least 3) over the pistons. The result will be a bit more even compression/displacement, but if you dont do the area around the valves, you wont get perfectly even compression. Will it appreciably matter?? I didnt do the valve chambers. I dont recall if she ran noticeably rougher. But what the heck a rough running motor @ idle is a sign of "high performance"

[RVA23T]

#2 home heating oil
Elbow grease
Brake cleaner
Woven pads such as scotchbrite white or gray
Brass wire brush
Rags
Brake cleaner
Elbow grease
Time

[Craig Leach]

First remove the carbon from the pistons!!!!! run the piston almost to TDC grease the bore, run the piston to TDC clean off all the carbon you
can with scraper & wire brush, power works best, wipe all the grease you can off the piston & cylinder. drop the piston down & wipe the grease
off the cylinder. Cover everything you can to keep it clean on the parts you are not working on. Check fast food drink cup lids. ( some fit right
into the bore & seal it very well) Aluminum foil works great for masking to keep crap out! the holes in the valves do not guarantee the valves
are two piece valves but if they are now is the time to replace two piece valves. If you have to remove material from the head or pistons
patience is your friend.
Craig.

[Allan]

You might try the Prussian blue Dan mentioned. It will show areas in contact.

When you fit the head, do so with a pair of pistons at the top of their travel, when the intrude farthest into the combustion chamber. This will help at least two pistons to centralise the head around those two pistons. Crank it over by hand to see if you still have a problem with the other two. In my experience with Z heads, you will need to relieve the sides of the combustion chambers so they clear the pistons.

The real answer is use a Prus head. They are a quality product.

Allan from down under.

[ModelTWoods]

Others may differ, but since a T engine's pistons are two up and two down at any one 180 degree cycle, when you have two up that you want to clean, to keep debris for falling into a cylinder bore where the piston is down, cover the 'down' cylinder bore on the engine deck with "painter's tape, so the carbon you scrape off doesn't go where you don't want it to go.

[Dan Hatch]

First get rid of those two piece valves before you lose one and knock a hole in your new head.

[Jonah D'Avella]

Ok! sounds like i have my work cut out for me! first, i do have some experience with machining, i am going to school for metal fabrication and have completed 2 classes in manual machining, i considered machining the head, but there doesn't seem to be much material there to machine, i worry about compromising structural integrity. Is that a problem considering that it looks like it lifts the head on one side about an eighth of and inch and that might take a good bit of material off? also, how do i know if my valves are 2 piece? also, i saw on langs, there was a modern style valve that's supposed to give more power, what would it take to install that? Item Number: 3052M

Is it worth it to keep this head, with pruss heads available? should i just save up and buy one instead? I would have bought one initially, but i just couldn't afford it.

[Dan Hatch]

The 2 holes in valves show they are original Ford valves. The heads break and can do damage.
You can use the new SS T valves if your keepers are good original Ford.
Stay away from reproduction keeper washers.
There is an old post about why?

[Kerry]

The 2 holes in valves, 1 piece, were available well into the seventies at my end of the world for any engine, the holes were for the lapping tool.

[Dan Hatch]

Here is a link to thread about repro washers.
http://www.mtfca.com/discus/messages/50 ... 1450555390

[greenacres36]

Are those Ford Y block pistons? I have them in my car and it looks like someone machined the top of them to make them clear the head.

[speedytinc]

Are those Ford Y block pistons? I have them in my car and it looks like someone machined the top of them to make them clear the head.

No.
Y block pistons don't have that much material above the top ring to machine.
They are & need to be near flush with the deck.

[John kuehn]

Here’s a picture of Model T aluminum pistons in std sold by Lang’s just for comparison. They do look pretty close in the dome height as the ones Jonah posted. But of course I could be wrong.

[Gene_French]

Jonah:
the height of a standard Model T piston above the block is 5/16 " ( .312") ...that assumes standard length connecting rods (7.000 center distance ) and a un-machined deck on the block ... any additional projection above the block deck will reduce clearance within the chambers of the cylinder head ( and raise compression ) ... on every Z head i have installed there was interference on #2 and #3 pistons ( 7 heads ) ... likely due to warpage during the cooling cycle after casting ...Gene French

[ModelTWoods]

Ok! sounds like i have my work cut out for me! first, i do have some experience with machining, i am going to school for metal fabrication and have completed 2 classes in manual machining, i considered machining the head, but there doesn't seem to be much material there to machine, i worry about compromising structural integrity. Is that a problem considering that it looks like it lifts the head on one side about an eighth of and inch and that might take a good bit of material off? also, how do i know if my valves are 2 piece? also, i saw on langs, there was a modern style valve that's supposed to give more power, what would it take to install that? Item Number: 3052M

Is it worth it to keep this head, with pruss heads available? should i just save up and buy one instead? I would have bought one initially, but i just couldn't afford it.

Jonah, The "modern" valves in Lang's catalog, are Ford 351 Windsor exhaust valves, if I'm not mistaken. They require a special hardened valve seat to be installed by a machine shop in the block deck to use. I have never seen where you could just use a valve cutter to open up the valve seat area in the block without using the appropriate size replacement valve seat. The stems are .030 oversize and will require reaming. Small block Chevy valves can also be used, but their stems are also .030 oversize (if I'm not mistaken) and guides would have to be reamed. Chevy valves don't have as big a diameter of head as the Ford valves and I don't think require (although its probably recommended) to use a replacement valve seat in the block's deck. Even with a Z head, without a higher lift camshaft and more carburetion, larger valves are not going to be worth the expense and effort. Now, if you were using a camshaft (new or reground) that had at least .280 lift and improved or modified carburetion, then the larger valves would be worth the effort, and expense.

[SurfCityGene]

Looking at that scale in the first picture it almost looks like top of the piston is 3/8" above the deck??

[Allan]

Those may not be two piece valves. The two piece ones with which I am familiar, have just two holes drilled for the lapping tool, not the three shown on these. The best way to check is look through one of the ports on the engine side. Some replacement one piece valves were drilled for the lapping tool.

Allan from down under.

[Jerry VanOoteghem]

Those may not be two piece valves. The two piece ones with which I am familiar, have just two holes drilled for the lapping tool, not the three shown on these. The best way to check is look through one of the ports on the engine side. Some replacement one piece valves were drilled for the lapping tool.

Allan from down under.

I thought the same thing when I saw the center holes.

[Craig Leach]

Skinny block cheby exhaust valve stems are 11/32" 0.030 oversize stem. they do not require a hardened valve seal although that is
recommended. If you use the stock valve spring retainers the installed height of the spring is a little long. You can buy special keepers
that correct this.
Craig.