So i ended up getting the CP 8:5:1 comp ratio pistons brand new for 250 plus a road trip. :) and my Eagle H beam rods. Got my block being bored .20 over, crank turned head remilled..etc

Shop calls me, says pistons are wrong stroke and wont be flush with the top of the block. Im thinking he must not know about these pistons rods in the 420a too much or he didnt connect them to rods and bolt it to the crank with bearings in the block.



My question is how many people have used CP pistons? AND if its not flush with the top of the block will it still work?

I've done some searching and so far no luck. Any suggestions?

Work? Prolly but there are a lot of uncertainties if you dont know what your using. If the piston is not correct then your compression ration is going to be significantly less.


You need more info.
Piston Part number?
How far are they below deck?

Typical installs have the piston below the deck .005-.0020 depending on engine/piston ect. Very few motors are truely flush at .0000

No one installs rods and pistons in a motor without the bearing becuase the crank can get scratched very easily so i highly doubt your are accurate on that.

If you cannot identify what the P/N is on the pistons and they are sitting .500 or more below the deck then get rid of them and just buy a new set. New CP pistons are only 400.00

You can order a piston made for any style of combination. If those pistons were ordered for a stroker or a long rod combination then they are pretty much useless to you. Its very common for special order pistons to be purchased to the customer specs.



EDIT: looking through CP catalog, they do list 420A pistons anymore which means they are special order only. The SRT4 has the same bore as a 2.0L which makes me wonder if your looking at a 2.4L piston. I cant find the compression height or either piston online to compare but a 2.4L piston is made to sit well below deck. Off the top of my head i would say they sit .200 below. If your pistons have a dome top and they are speced at 8.5:1 then you most def have 2.4L pistons.



Edit: Ok found the figures i needed.

2.0L info:
Deck Height: 212.0 mm
Rod length: 139.0 mm
Stroke/2: 41.5
8.8:1 piston Comp Height: 31.3

Do the math and the piston will sit .200 below deck and thats on a 8.8:1 piston. Order a lower ration and the piston will sit farther below deck.

2.4L info
Deck Height: 238.14 mm
Rod length: 151.0 mm
Stroke/2: 50.0
8.5:1 piston Comp Height: 35.5

Install 2.4L piston in a 2.0L block at the piston peak will stick out 04 mm and the landings will sit pretty far down below deck. A 2.4L piston is a dome piston.

Now if you have a domed piston but the dome doesnt appear to stick out 04 mm then dont rule that out becuase its very easy to take a domed piston and mill 04mm off the top to make it work on a given application. Machine shops do that all the time to drop the compression of a high compression piston.

Now if you suspect you have a 2.4L piston after reading this then do not assume an 8.5:1 2.4L piston will equal 8.5:1 in a 2.0L stroked motor. Just becuase the bore is the same, the stroke is far less and that will factor in to the comp ratio. I wouldexpect to see the comp ratio below 7.9:1.

Now if you managed to get a long rod piston, that piston has the wrist pin relocated 0.138 farther up towards the ring lands. So lets say the piston normally sits .200 below deck, installing a long rod piston would sit 0.338 below deck. This will again drop the compression ratio down more than you realize. In addition to that skirt clearance and piston stability may be an issue at the bottom of the stroke.

Terry

Yup, this isn't about the piston manufacturer, its about the application of the pistons. What were they made for? 420a? 2.4? SOHC 2.0? Stroker? 4g63? Do you remember seeing valve reliefs? (though its all guess work right now)

Gotta pull numbers off the pistons and find out. Also, find out how much below the deck.

Oh fuck, Terry's editting in info as I speak! Go to bed jackass. You got an extra hour of sleep tonight.

Some of us work night there, Tennesee Tea!

I do not have the pistons with me as of the moment, i gave them to the machinist to bore to the exact size to each piston. I am pretty sure it said 420a on the side of the box in there somewhere. it also said on the bottom of one of the pistons in perm. marker stroke 10.5 88mm.


Now Rick ( machinist) Called me and said the only way i could use these pistons is if i got longer rods and a diff crank. He said they sit lower then the top of the block. And that they are about a half inch different from the stock piston.

Wouldnt forged 8:5:1 pistons be smaller then oem 9:6:1 pistons anyway?

I am just gonna go ahead and have him bore the block .20 over monday.


Yes the have the half moon cups on them. They are the same exact pistons as the ones i seen in 'slo2g's" build.

I cant get you a P/N until monday since he has the box as well. I just have photos of them for now.

10.5 Stroke???? Whats written on the bottom is useless. 10.5 is not the stroke.

a full 1/2 shorter overall is not a piston you can use.

The 2.2L crank used an 89MM stroke which used a 138.98 MM rod. That would only put the piston 5mm higher. Thats not even a 2.2L piston.

I have no idea what those are but if you believe whats written on them and what box they are in then I have vacation land in the everglades to sell you.

Well i have no idea why it would say stroke 10.5 and the 88mm was the last 2 numbers written in a group of them on the same piston. Im clueless to why it would say that. Ill find out tomorrow the part number serial numbers, all that shit. Im pretty positive they are the right pistons. I called and talked to the guy i bought then from, he said he bought them for just your normal everyday build. and they arent stroker pistons.


But let's say that they dont come flush with the top of the block, what are the risks im looking at?


The pistons look the same on the top as the OEM pistons. but the bottoms are different obviously.

Originally posted by ryan95eclipse
it also said on the bottom of one of the pistons in perm. marker stroke 10.5 88mm.

I want to wait until tomorrow to see numbers but, I'll take a shot at this; stroke 10.5 88mm = Stroker with 10.5 comp and a bore of 88mm (as in .020 over). Which, in taking a leap of faith, may be 2.4 pistons (i.e. "Now Rick ( machinist) Called me and said the only way i could use these pistons is if i got longer rods and a diff crank."). Of course they could also be special order pistons.

Originally posted by ryan95eclipse
Wouldnt forged 8:5:1 pistons be smaller then oem 9:6:1 pistons anyway?

Normally, the dome would be different. But certainly it would not have 1/2 inch deck difference.

Originally posted by ryan95eclipse
But let's say that they dont come flush with the top of the block, what are the risks im looking at? .

1/2 inch short and you'll have to race unmodified automatic Pinto's (and lose). You will have extremely low comp. It is not an option.

On the bright side, you probably won't have to worry about being an interference engine anymore :shrug

Originally posted by ryan95eclipseI am just gonna go ahead and have him bore the block .20 over monday.

I hope not, lol

And one more punchline; ask the seller if he got those from DSM Graveyard. Just a shot, but it would answer a lot.

Ok that does say a lot. Rick did say that if i were to use these pistons the compression would be low and 5:1. i then told him that they are 8:5:1 and thats when he said no and lost it. Tomorrow ill update this with the numbers. Maybe a few pics.

Talked to dude and he said he bought the pistons at a local performance shop in the dayton, ohio area.

So i went n picked up my pistons today and noticed the difference. got the only numbers that are on the box


under the piston it says cp 86-2

and on the box it says 540p88-s and what looks like either
55520 or 55820


Yes the wrist pins measure .827 and thats the exact size as they oem wrist pin.

Im gonna attach some pics i took, quite a few so bare with me.

Sure do look like stroker pistons (hence the shorter skirt and the shorter deck. Meaning they would come down the bore further and go up the bore further).

But I can't seem to get anything out of the numbers. I think you're now at the point of calling CP to identify. The 86-2 is just a casting numebr for that slug (I did find it in a Mustang, lol). The other numbers may be job lot numbers that they can identify.

Funny thing is, where the writing is, is where you would expect to see the ID numbers.

Thats hardly 1/2 inch difference. Your machinest is an idiot and I would not use him again. That is most likely a 2.2L stroker piston. Go back and look at the figures i posted since apparently i am talking to the wall here.


a 2.2L piston will need to be 6mm shorter to fit. Just by looking at the picture.....looks pretty close to 6mm shorter.

Thanks guy. I just listed them on ebay and hope they sell. I should be getting a fat check at the end of the week, if it goes right i could buy pistons and a turbo kit ;)

i cant use em so why make em work? Just gonna pick me up either set of them. Wisecos or if the check is good enough Je's.

Originally posted by ryan95eclipse
Thanks guy. I just listed them on ebay and hope they sell. I should be getting a fat check at the end of the week, if it goes right i could buy pistons and a turbo kit ;) i cant use em so why make em work? Just gonna pick me up either set of them. Wisecos or if the check is good enough Je's.

http://cgi.ebay.com/ebaymotors/NEW-420a-CP-8-5-1-88mm-Pistons-_W0QQcmdZViewItemQQhashZitem3362701431QQitemZ220694844465QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

http://www.raceeng.com/p-11777-420a-stroker880mm851-dohcrings-set.aspx

You need to take two seconds and call CP to confirm, but raceeng.com only lists 8.5:1 88mm pistons as stroker pistons.

:thumbsup Terry