Top piston ring wear?

The later pistons look like they have the valve head pockets in them from the not too clear picture and the the earlier ones just a bigger hollow in them. The SN 7J to 833 shows the deeper dish and 834 up the later one with the shallower dish in them. It doesn,t show if there are valve pockets in them as the picture only has a side ways view so I,m guessing then the shallower dish has the valve pockets in the top. Most all later engines in tractors have the valve pockets in them.

Here is a pic without the valve reliefs

[img]http://c2.ac-images.myspacecdn.com/images02/63/l_91180dc8d3754fb2a7e807e6324ab245.jpg[/img]

Here you can see the valve reliefs

[img]http://c2.ac-images.myspacecdn.com/images02/44/l_f549d7643e0b4081ad6a68eb784e953d.jpg[/img]

I see. So this one is supposed to have a deeper dish and no cut outs for the valves. It is a 7J9XXX. There is a scrap yard close to Nocona that I may try. I am just wondering if the height of the pistons is different since some are cut out and others not.

Thanks,
John

As I stated before the 7J 834 and up has the shallow dish and the valve cutouts in them going by the parts book.

My 7J3168W was rebuilt at one time and was assembled using 4 different PN pistons. None of which had valve reliefs. The new one in the pic is a sealed power piston. I gave away the 2 good pistons I had and may have one around to measure, but I really don't think it'll make much difference on how it will run no matter what piston combination you use as long as they are serviceable pistons. Make sure the tops are tight if they are 3 piece pistons, and hopefully pinned. If they are loose this will happen.

[img]http://c1.ac-images.myspacecdn.com/images02/42/l_55c367f8417c42d6891cba5e83e8a14c.jpg[/img]

There would have to be at least a dozen different piston designs available for every Cat engine .. because Cat constantly improved piston design over the decades, and changed the piston design every 3 or 4 years, as technological advances were made. Add to to this mix, the aftermarket design pistons that often have design differences to get around Cat "registered design" and patent restrictions.

Over the decades, the number of piston rings shrank from 6 to 4, to reduce friction losses .. cast iron inserts were thought up .. then changed in design, as initial problems were found and overcome.
The wrist pin retention method changed from plugs to snap rings.
Ring design and position on the piston changed numerous times, as improvements in performance were sought .. and pistons themselves were redesigned .. to reduce weight .. increase strength (particularly in the piston crown area) .. and cam-ground pistons appeared as well.
There were several different piston crown designs, as enhanced performance was sought.
Two-piece pistons appeared in the late 1930's, and were redesigned in the early 1940's to improve piston top retention .. then the two-piece design was scrapped in the late 1940's.

If you're rebuilding an engine, and you want excellent, long term performance and reliability .. it pays to ensure that all pistons are the same weight .. are similar design .. and have the same dimensions, particularly the wrist pin-to-crown dimension ..
It also pays to ensure that piston ring grooves are in good shape .. ring clearances are within specs .. and that liners aren't badly tapered or out-of-round, nor grooved, nor scored.

The bottom line is .. the closer you get the parts you're installing, to within new specs .. the more chance you'll have of an engine performing like a new one.

That makes sense. Thanks for the info. I have always heard that cat made some good pistons. One of my neighbors is an old tractor puller and he always used cat pistons in the engines he built because of there strength.

I would like to have the engine perform like new so I will continue the search for some pistons. Will the ones without vavle indentions actually increase the compression ratio?

I have found that there can be variations of head design and that is the reason that some pistons are cut to clear the valves and some are not, if your head is flat and the valves protrude below the surface of the head then your pistons need the relief cuts as to not hit the valves if the valves are recessed into the head as in you can run a straight edge across and not hit the valves then either piston will work. Just check the piston at TDC so you don't have a piston come into contact with the head, bad things will happen.

Now I may be wrong about the 4 1/4 family of engines but I know it holds true for 5 1/4 and 5 3/4 engines that not all pistons work with all heads.

d75 has beat me to it, somewhat .. but the piston design is related to the other engine parts at any one particular time, and you need to check the parts book .. plus double check clearances and fits .. to ensure you have the correctly matched pistons, valves and heads, with regard to P/No's.

The piston cutouts can also be related to redesigned, thicker valve heads, or different valve seat designs, according to head P/N. Cat diesels use flat heads, and the compression ratio is governed by any dish in the piston, and clearance between piston crown and head surface.

I'm not aware of any major changes to the compression ratio of the naturally aspirated D4 .. which was around 16 or 17:1. Turbo'ed engines generally have compression ratio reductions, but that doesn't apply here.