Wrong pistons?

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration
Model T Ford Forum: Forum 2012: Wrong pistons?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Chester Leighton on Monday, October 29, 2012 - 10:17 am:

Back in 2009 when I was going through the engine on my 26, I bought new aluminum pistons from Langs. This was my first car restoration so I was reading the parts descriptions to figure out what I needed. I just pulled up my invoice from Lang's web site( a great feature I might add)and looked at the part number. It was 3021.020. In the current catalog they list 3021.std with the 0.020 oversize being listed as 3021.020 and 3021.HC for high compression pistons. It says in the description of the high compression pistons that they fit 1909-27 but that they can't be used with high compression heads. At the time I ordered the pistons, I thought that the 26-27 had high compression head so I bought the "standard" pistons which were also described as "fits all model T engines from 1909-27". I figured the high compression pistons were a upgrade for the low compression head engines which would likely have more clearance for the higher dome of the piston. The pistons I received and installed were flat top where as the original cast iron pistons were domed and stuck up above the block a little. I have had my T on the road for about a year and have a little over 1500 miles on the engine. It starts and runs well but lacks hill climbing power. I live in central Virginia so there is no escaping having to climb hills. Having learned and studied more on the engine since 2009, I got to wondering if my lack of power is because I have flat top low compression pistons installed instead of the domed high compression pistons? Can someone help point me in the right direction?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Monday, October 29, 2012 - 10:41 am:

Chester,
The flat top piston that you installed are the standard pistons for your car. Originally the engine is supposed to put out 20 hp, that's pretty low power and normal. That's how it came from the factory.

If you do not have a high compression head you could add the domed high compression pistons. Or, you could add a high compression head and use the standard pistons you have. Either way you will get a little more power with more stress on the engine and less engine life. Your choice.

Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Charlie B actually in Toms River N.J. on Monday, October 29, 2012 - 10:49 am:

Chester those flat topped pistons have got to be keeping the compression pressure down (with an original head). Take a compression test and find out what you've got. It should be quite revealing and low. You state it's re-built with 1500 miles on it so I'm assuming the internal's are OK & broken in. What to do about it? Don't raise the bridge, lower the river. In this case, lower the head. In other words a high compression head will restore some power by "filling the gap" left by using flat pistons. Beats the heck out of pulling it down again.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Charlie B actually in Toms River N.J. on Monday, October 29, 2012 - 10:53 am:

You did say it had domed pistons when you tore it down. Putting in flat tops, correct or not had the effect of enlarging the combustion chamber and therefore lowering the compression pressure and power out put.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Larry Bohlen, Severn MD on Monday, October 29, 2012 - 10:53 am:

Chester,

I'm sure some of the guys will chime in but you did fine putting those pistons in. By using the flat tipped pistons you can use a Z or other high compression head if you had used the domed pistons you would not be able to. For some folks it's a choice but most folks like to use a Z head.

I would spend a few bucks and buy a Z head you should be able to take the hills on then.

Larry


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Monday, October 29, 2012 - 11:06 am:

Several other things than the pistons affect the hill pulling abilities. The body style and whether it has bumpers will make a difference, as will the number of passengers or other load. The gear ratio is probably the most significant factor. Also whether you are using magneto or battery for your ignition. Even the type carburetor has some affect. The camshaft you use will also vary from low speed power to high end speed. Before you spend money and effort to replace the head, check out the other things as well. The head might please you or it might disappoint you, but it will be harder on the rest of the engine.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Charlie B actually in Toms River N.J. on Monday, October 29, 2012 - 11:50 am:

All the more reason for a compression test. Find out what you've got compression wise and you'll know where to go with your head. Mill it or replace it. You're looking for that bit of oomph you've lost. Not building a speedster engine.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chester Leighton on Tuesday, October 30, 2012 - 03:07 pm:

It's a little cool here in central Virginia today so I started the T and let it run a few minutes before doing the compression test. I didn't get it up to full operating temperature but let it warm up so it would turn over at normal speed when cranking on the starter. I had the throttle wide open and all plugs installed except the cylinder being tested. I got 46psi on #1 cyl., 45psi on #2 cyl., 40 psi on #3 cyl. and 45psi on #4 cyl. This tells me there may be a valve adjustment or valve lapping opportunity on #3 cylinder but it isn't that far off the other three. This is my first T so I don't know if 45 psi is good or bad. The engine runs smooth and starts up with out trouble, it just doesn't pull hills well. I'm running champion X NOS spark plugs and a Texas T distributor on 6V system. Again, I thought the 26-27 engines had a high compression head on them. The stock pistons I removed had a dome top that came above the top of the block slightly but the new aluminum pistons that are in it now are flat tops.


Top of pagePrevious messageNext messageBottom of page Link to this message  By keith g barrier on Tuesday, October 30, 2012 - 03:16 pm:

Chester, I know some will dissagree, but I know that on my 24 2 door I had much better power with the stock cast iron pistons. All I changed was the pistons, still standard bore. Also the engine ran much quieter with the stock pistons. The only reason I changed them out was I messed up and ordered the wrong rings and rather than send them back, I ordered aluminum as everyone said that was the thing to do. I drive about 35 so could really tell the difference on the hills, have to get a good run and go now. KB


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Tuesday, October 30, 2012 - 03:17 pm:

Chester,
You should leave all the spark plugs out during the test. The result will likely be a little higher.
Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Tuesday, October 30, 2012 - 03:42 pm:

Both Chester and Keith have noted that after replacing the pistons the car had less power. Could it be the pistons and rings are still tight and the rings have not yet seated? An engine which has been broken in will run better than one recently overhauled.

Drive it around a while and then report on whether it runs better. Also drive around a while before you do any big changes on it. You might be surprised.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By keith g barrier on Tuesday, October 30, 2012 - 04:03 pm:

Norman, my engine has around 30k and still does not have the power it did with cast pistons and worn out rings. Coils are better than I had as they have been rebuilt and set on hcct. so all variables have been checked. KB


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan Hatch on Tuesday, October 30, 2012 - 04:56 pm:

How were the valves set? Dan


Posting is currently disabled in this topic. Contact your discussion moderator for more information.
Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration