Wiesco pro tru piston:

Hello everyone,
People running Wiesco Pro Tru pistons ever measure top ring groove depth? Found that D wall demension of ring is greater than piston groove depth. Anyone else measure and find this to be true?

 

So your stating the depth of your top ring groove is less then the second ring groove?

 

Yes,called Wiesco and they stated that the ring groove depth is .196"...
D wall for 4.350" bore is .1977"

 

D-wall: A specification established by the Society of Automotive Engineers (S.A.E.) that dictates the radial width of a standard automotive piston ring by the use of the following formula: Bore diameter divided by 22 = radial thickness (3.386” divided by 22 = .154”)



So for us not in the know, what does all this mean. Just bought a new set PT for a motor

 

Exactly... Piston rings need a back clearance of .005" so add .005" to the D-wall figure and this is what your piston ring groove depth should be.

 

I guess this would depend on the RI gs they used correct????? Plus my pistons says to have .0045 piston to wall clearance. So if your dwall is .1977 at 4.350, and the groove depth .196 on a piston that 4.3455 that would put the back of the ring groove at 4.1495. The inside of the ring would be 4.1523 that leaves a back clearance in theory of .0028. I would guess one should measure the ring thickness and verify they are .1977 mine are in MI and I'm in Ohio so I cant. I bet the rings are close tor to 1.975

 

I measured my rings, and the radial dimension was between .1965" to .2030". Called Hastings and Total seal and .1880" to .2050" are within production tolerance. The ring will stick out of the groove and that is not ok.

 

You need to measure the piston's diameter @ where the ring grooves are machined in, that diameter is smaller than the skirt diameter. As long as the rings don't stick out of the groove bigger than the cylinder's diameter you should be good.

 

If you want a blacksmith way of checking this, put the ring in the bore and measure the ring gap, if that is within spec. put the ring on the piston and squeeze it together, if it butts you don't have a problem

 

There you go a simple easy way to check from a man in the know

 

Just spoke with Wiesco again... they said PT5055H4 (my piston) has been discontinued and the ring groove depth issue has been addressed on newer pistons. If you are running a Wiesco piston, please check the top ring groove depth.

 

Bumner, mine were just ordered not sure of the part number but I think they should had been pts543a4. Wonder if since they know there was an issue is they would be a stand up compaby and trade you ones not made right for ones made right

 

Yeah, the pts543a4 is the flat top version of their piston. Wiesco said my pistons are too old, and I should have caught this when I first bought them... They also tried to tell me that they had a differnt spec ring they used on the older piston. I called him out on it and said that your catalog listed a Hastings 4350H ring, same as new piston and used the SAE std d-wall spec. After I said this, then he said i should have caught their screw up on first assembly. All I can say is when dealing with any after market parts you must inspect everything. Most of this stuff is low volume and not a whole lot of R&D goes into it.
The consumer becomes the tester...

 

Sad but true.
I had a '66 427 Original Numbers Matching Roadster sent to us from Palm Springs CA. During the engine rebuilding process we had buttoned up the whole short block but I wasn't happy with a couple miss matched main studs. So I ordered Brand New Main windage tray studs right from GM. I removed the mismatched studs. I took the new studs out of the GM packaging, cleaned them, and during torquing process one of them let loose and pulled 1/2 the threads out of the block. Turns out that one stud had a taper of about .030 in it. Couldn't see it if you weren't looking really close. Had to disassemble the short block, send it out for thread insert. Wash and reassemble. Lucky the line hone was still spot on. Contacted GM's Rep and the best they could do is give us a new stud. After that we try to not only check everything, ..... but we try to find things wrong in the parts manufacturing. I must admit that I haven't checked any piston ring lands for problems such as yours, but I will now.

Larry

 

Bummer! definitely a learning experience...

 

So how shallow is the ring grooves for the rings? What size would the bore need to be to be able to use those pistons?


Here is what you may be able to do to be able to run those pistons;

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As long as its not more than .040" more overbore(.020" per side) The above coating should get you back in business if you want to use those pistons.

 

I am having the ring grooves cut to the proper depth. Thanks for the info though.

 

This is great, but sad, info. I have "old" Weiscos I bought 10-years ago. Was getting ready to fire the motor but was not comfortable in doing so. It seemed too tight. Now I think I know why.

I should have, but did not, check the depth of the ring. Didn't occur to me to check the manufacturing tolerances of a piston made by a "reputable" company. Of course, I should have.

Who is cutting your ring grooves to the proper depth?? Doesn't seem like something that your "average" machine shop could do--or would want to.

Best,

Ranger
Aiken, SC

 

You have to check more than you think regardless of company reputation.
There's ranges of tolerance in everything and sometimes they aren't to your favor.
I would expect anyone with a lathe, a groove tool, and the willingness to indicate them into the chuck would be able to do it. It's time consuming, sooo...
The corner automotive rebuilder might not view this as profitable,if that's what's meant by average.
The close you look and the harder you run things, the more you end up budgeting in corrective machining to be able to fit these together.
Ask any place how much corrective machining they've given away to assemble them 'right' and you quickly learn why many machine shops limit themselves to just cutting the parts to nominal and handing them to you blamelessly.
(Not defending any shops or manufacturers here).

I wonder if there are rings out there on the low side of the spec or if you got a set for a .010" smaller bore size would they clear?
(not because the OD is smaller, but because the spec used might have been calculated smaller as a percentage of the bore)​