Piston rings and size . Help

Talkwrench

Talkwrench

Well-known member
Guys I need help, building a 37. 221 and the pistons I have ( ford 3 ring domes ) are stamped . 030. I purchased .030 over rings and went to fit and there was a .030 gap..? I ordered another set thinking they must have been in the wrong package, well these are also .030 gap. The machinst said the pistons must be marked incorrectly and to get .040 over rings. Yes the pistons fit nice in the bore. So I'm just double checking that this sounds right, is there a formula to use knowing that there is a .030 gap now??

Cheers.
 
You should measure the actual bore size. Just using calipers should be close enough to determine whether the bores are .030 or .040 oversize.
 
Again the curious me. Wonder if you stuck your new piston in the bore with a feeler
gauge and got a good or pretty good fit? And measure the bore as Fritz said, then
measure the new piston even with a caliper (guess-0-meter) the naked eye can see
the difference. Also common is pistons that are not marked, thats when I measure
things 10 times. Old saying batches of parts made on Friday or Mondays. I think something is stamped wrong.. So before more ring money ya got to know the true piston size /bore size. Remember all valve in block engines are well forgiving !
 
Presume the 30 thou gap is the ring gap when the loose ring is positioned squarely in the bore. If you use 40 thou over rings in the same bore the gap will decrease too much.
 
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If you do indeed have an end gap of .030 with the +.030 rings then the +.040 rings will close the gap to a point where they will have to be ground to achieve the desired gap.

Pi x 3.093 = 9.717 circumference ( +.030 rings )
Pi x 3.103 = 9.748 circumference ( +.040 rings )
9.748 minus 9.717 = .031 which will close the gap.
 
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Sorry having a double senior moment. Too cold in the workshop, “Beast from the east” Driving me mad staying indoors! Hope it warms up soon.
 
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You need to check the ring gap at the bottom of the cylinder bore. It could be that your cylinders are badly worn at the top. The bottom of the bore will be a better indication of the diameter to which they were bored.
 
Something sounds very strange about this whole issue. The normal procedure is first you acquire the pistons you are wanting to use. Then bore/hone the cylinders to match the pistons. I see no way possible a machinist would not know the size of the pistons and the size of the cylinders. These two factors are needed before you purchase rings! Almost sounds like there is some guessing going on somewhere, am I not understanding the situation?

At the very least, you need to back up at this point and measure things so you know where you are. There should be no "guessing" as to what piston size you have, or what cylinder size you are working with! After establishing sizing, put the pistons in the cylinders and measure the clearance between the piston and cylinder wall. Order the correct rings based on the correct piston size.

Engine rebuild manuals will show how to measure piston/cylinder clearance. But still a little difficult to believe a machinist doesn't understand all of this.
 
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Take a piston out and run a taper gauge down the whole bore. You say nothing about the block. Is this a tired engine that was smoking that you used a ridge reamer on and ran a ball hone down the bores thinking new rings would fix it? Like suggested above bore taper may be the culprit. Careful measuring will reveal where the problem lies.
 
It has already been mentioned place a new ring square the bottom of the bore and confirm end gap. Now do the same in the middle and top of the bore and report back with your findings.This requires no tooling just a little time. It is quite accurate to determine your problem.

R
 
Yes the pistons came first once I checked it was a standard bore, I found them locally [+ 030 presumably as stamped] . The engine been bored & honed to suit the pistons. I purchased the rings when I made a complete order up of stuff from the USA , I cant get rings here [ I had to take the chance].


To replace the original set the machinist wanted me to try and get a set of gapless rings , he wanted to set the gap himself [he didn't want me to do it] . Anyway after me inquiring with my normal U.S. supplier he could not find any sort of thing and... yes this is where we assumed that the original rings were in the wrong box and just ordered another set.


Its a bit of a crap situation because parts aren't readily available here I have to source all of it, I know he tried to get rings locally but, no one has these sizes and it gets thrown back to me to sort it out and half the time it like Chinese whispers..


All I can tell you is that when I was in there I checked it with the head engine builder [ he normally doesn't look at my engine its the owner of the business that's had it under his wing ] We put a ring in the bore [we knew straight away it wasn't right] measured it and yup.030 gap , he simply said your pistons are marked incorrectly get a set of .040 rings.. I said are you sure that'll do it ? "yup absolutely" .


So this is where Im at and needed to double check with you guys if a set of .040 will close up that gap @ .030


Aghh I cant begin to tell you how much of a cluster f *%$k this has been .. Its coming on 12 months and Im still not ready to button it up ...




JSeery said:
Something sounds very strange about this whole issue. The normal procedure is first you acquire the pistons you are wanting to use. Then bore/hone the cylinders to match the pistons. I see no way possible a machinist would not know the size of the pistons and the size of the cylinders. These two factors are needed before you purchase rings! Almost sounds like there is some guessing going on somewhere, am I not understanding the situation?

At the very least, you need to back up at this point and measure things so you know where you are. There should be no "guessing" as to what piston size you have, or what cylinder size you are working with! After establishing sizing, put the pistons in the cylinders and measure the clearance between the piston and cylinder wall. Order the correct rings based on the correct piston size.

Engine rebuild manuals will show how to measure piston/cylinder clearance. But still a little difficult to believe a machinist doesn't understand all of this.
Click to expand...
 
51 MERC-CT said:
If you do indeed have an end gap of .030 with the +.030 rings then the +.040 rings will close the gap to a point where they will have to be ground to achieve the desired gap.

Pi x 3.093 = 9.717 circumference ( +.030 rings )
Pi x 3.103 = 9.748 circumference ( +.040 rings )
9.748 minus 9.717 = .031 which will close the gap.
Click to expand...


Brilliant !
 
How in the hell can the machinist not know if the piston is in fact .030 over or not??? That is the strangest thing I have ever heard. If they don't know what size the pistons are then how in the world do you know the cylinders are finished to the correct size. This is totally bazar! I feel for you, but until someone figures out what size the pistons are and what size the cylinder bore is you are spinning your wheels. Doesn't the machine shop have any measuring equipment?

If the engine started out near standard, how did they bore it if they didn't know the piston size? I mean measure the piston, not going by some marking on it. How did they check piston fit/clearance. This sounds like Alice in Wonderland to me, maybe I just do things different. I really feel your pain on this one!!!
 
If you sent an email to Hastings stating the finished bore size and the ring widths number of compression rings and the number of oil rings they could build that set in a heartbeat. And they will supply the part number as well.Rings generally are made by size and not application.Just tell them what engine you have and it will happen.
From the info supplied you need a more competent machine shop.

R
 
Like JSeery, I can't understand how anyone who calls them self a machinist would assume what was wrong without measuring the pistons and the bore again. As stated above, you have to know the clearance recommended for the pistons to bore and hone the block which apparently has been done. Since we are dealing with a fresh bore, there won't be any taper so simply measuring the bore and a piston should clear up what the size actually is. Perhaps the boring machine was set wrong or set to a metric value or some freak thing like that whatever it is it shouldn't take more then 5 minutes to zero in on what you have and what you need.
I'm sorry that you are having this "experience". Don't let it sour you on the engine, it should however sour you on the shop where the work is being done.
Good luck and I hope you have a good resolution.
 
Worst case you can go for the next size overbore, and make sure they know how to do it. After everything is satisfactory you can measure your other parts and put them on Ebay to recoup some of the expense.
 
Well they must have measured , the pistons felt an ok fit to me. So really I should go measure it myself by the sounds of it.. See what they measure at ..
No I wont be going for an over bore or anything like that its all been balanced I don't want to go through that all over again .. I tell you Im worried the worst is still to come as I'll be assembling it and god knows Im going to find out something aint right .. Pfft!!
 
As already stated, the rings should not be an issue at all if you know what your bore/piston size is. The ring supplier should be able to provide just about any ring size you could want. I would forget ordering them based on any piston markings and just get the measurements. Would probably be best if you could talk to a supplier. I would think there would be suppliers in Australia. Do they order all the parts from the US? Have you tried to contact any fellow flatheaders that are somewhat local?

Any of the engine shops I have been around have catalogs of engines parts that list whatever you could dream of. They should have catalogs on rings by the specifications you need.
 
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