Question on CP 98" Pistons

[billbuilds]

     The CP 98" pistons come in four different compression ratios. Is there anywhere to go to get a visual of what the domes look like on the midddle two? I'm pretty that what I got aren't 9.5-1 but I can't tell whether they're 10-1 or 10.25-1. 

[Ohio HD]

CP generally supplies a spec sheet that tells you the cc of the piston dome. Also they'll list the height of the dome.

Here's a sample from the latest pistons I ordered.


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[billbuilds]

    I did not receive any paperwork with my return parts. Not even a receipt.

[Coff 06]

It's been a long time ago.When I bought my CP 98" the box was marked #98-10 to designate 10cc domes
Did you even get a box?          Coff 06

[Ohio HD]

I'm assuming that who ever you got these from isn't being helpful. So I'd call CP Carrillo tomorrow and ask then how to identify what you have. I'm sure they're technical support guys can give you some physicals measurements you could take. 

[billbuilds]

     Ok I found the piston spec sheet on the pistons in the box so pardon me for misspeaking.  I am not technically educated enough to be able to decipher the compression ratio from the available info so I'll call CP later today
There is no receipt however and after an email exchange it appears that he does not feel that one is warrented. 

     No Coff, there was no piston box. The rings were installed on the pistons and the pistons were just set into the top of the cylinders so that they rested on the bottom oil rail.     

[Don D]

The bullet series 98" pistons come in flat top, 3,6, and 10cc domes. These are shelf stock and based on CPs bullet series forging, a slipper skirt.

[Jamie Long]

On the bottom of the piston there should be two numbers; the CP job number and the piston part number (assuming its a standard CP shelf piston). The CP 98" pistons have the following designations:

BHM98FT -1.6cc 9.5:1 compression
BHM98-3 +3cc 10.0:1 compression
BHM98-6 +6cc 10.25:1 compression
BHM98-10 +10cc 10.75:1 compression

[billbuilds]

   I just got off the phone with a gentleman at Campbell Enterprises. He asked for the p/n on the spec sheet which is BHM98-10 (thanks Jamie Long). So this guy sent me 10.75-1 pistons which is way too high a compression ratio for the S&S 570's that he was well aware I would be using. Here's a photo of how I received the freshly bored cylinders and pistons. Notice what the piston is resting on. I am biting my tongue REAL hard.     

[kd]

You will still need to know the actual CC of the heads to determine the effect of the pistons you have.  Domed pistons can be used to compensate for large combustion chambers instead of machining the heads.  They may be OK and you won't know until you get all the numbers together to do a complete calculation.   Unfortunately that will include knowing the deck height so "some assembly required".

[Ohio HD]

Ok I found the piston spec sheet on the pistons in the box so pardon me for misspeaking.  I am not technically educated enough to be able to decipher the compression ratio from the available info so I'll call CP later today
There is no receipt however and after an email exchange it appears that he does not feel that one is warrented. 

    No Coff, there was no piston box. The rings were installed on the pistons and the pistons were just set into the top of the cylinders so that they rested on the bottom oil rail.     

Opps! I hadn't read down far enough and See Jamie has provided the dome info by piston part number already.


 

[Ohio HD]

I just got off the phone with a gentleman at Campbell Enterprises. He asked for the p/n on the spec sheet which is BHM98-10 (thanks Jamie Long). So this guy sent me 10.75-1 pistons which is way too high a compression ratio for the S&S 570's that he was well aware I would be using. Here's a photo of how I received the freshly bored cylinders and pistons. Notice what the piston is resting on. I am biting my tongue REAL hard.     

Wow, that's just poor thinking. 

[Coff 06]

I believe those pistons can be cut down to adjust compression ratio. Not what you want to hear with new parts sitting on the bench.
But just an option.          Coff 06

[billbuilds]

     kd, Thanks. Yes, I'm aware of what you're saying, I've plugged some numbers thru the Big Boyz calculator and it doesn't look real promising. those pistons have a dome volume of 10.4. Cams are S&S 570's. If you figure 85CC chambers (which I believe would have made that 9.5-1 compression mill run pretty flat) and an 045 head gasket you still end up with corrected compression of 9.6-1 and CCP a hair over 200. This does not leave much wiggle room head gasket thickness-wise if the piston are any more than flush deck height does it? 

     coff, Thanks, Thinking that I may have to go that route.

[billbuilds]

I just got off the phone with a gentleman at Campbell Enterprises. He asked for the p/n on the spec sheet which is BHM98-10 (thanks Jamie Long). So this guy sent me 10.75-1 pistons which is way too high a compression ratio for the S&S 570's that he was well aware I would be using. Here's a photo of how I received the freshly bored cylinders and pistons. Notice what the piston is resting on. I am biting my tongue REAL hard.     

Wow, that's just poor thinking. 

     Indeed and the more I think of it the more I wonder if he even bothered to put each piston in the respectively fit cylinder.   

[tdrglide]

Here is where you really need to know what cylinder head volume actually is. And measure deck height
Years ago I built a motor supposed to crank about 205psi according to the calculations. Couldn't figure out why it was over 220 until I took it apart and measured everything 

[Ohio HD]

Bill, if the cylinders are stock length, and not been machined, you should end up with the pistons 0.005" in the hole. CP's are pretty consistent as far as their compression height. On these it's 1.265". And if these are the OEM early rods for an 88" motor, they should be 7.667" long. An 0.030" head gasket should then give you a squish of 0.035".

You don't know for sure until it's together, but if all of the parts are standard size, this is what you should have.


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[billbuilds]

      Brian,   
      Thanks that's real good info and much appreciated. The cylinders are indeed early (1999) having come off the same motor that they're going back on.   

[djl]

As has been said, the OP needs to measure and equalize chambers as well as check deck height.  Having said that, assuming (has to be verified) that chambers are 85cc, deck .005", with a .040" head gasket and -4*on the 570s, corrected CR is 9.5 and CCP 199psi. In this day and age, with a good tune is very manageable.

Just saying that it seems there are a couple of ways to skin this cat without re-inventing the wheel.

My 98" is running fine at 10.1 corrected and CCP at 212psi. I do run premium fuel (93) but have no tuning issues.

[billbuilds]

    The chamber size turns out to be 79cc in one head and about .5 more in the other. I'm fine with keepping the ccp under 200. You can't always find 93 octane up here, especially when we have to change over to the summer blend, 91 octane becomes the high.

[Don D]

After all of that, just take a cut on the larger one .004

[JSD]

Is that correct in above? Positive piston down the hole in the Piston Deck Hight Chart. Just checking so i know as i thought the opposite. Thanks

[Ohio HD]

He's saying take 0.004" from the head gasket surface with the larger chamber, takes it down by about 0.5cc.

[Buglet]

  Before I would do anything I would wait until I get the pistons back then install then and check to see how far the pistons are down in the cylinder. If you are lucky you might not have to take the head down. Being you going this far you should check ever thing.

[kd]

    Bask in the warm fuzzy feeling you will get at the end.

[Ohio HD]

I would even the chambers out in the heads regardless of what the pistons weight or how they come back. That's part of the making things correct.

[billbuilds]

    You're right, I really should get those chambers evened out. Will I need to strip the head or will it be less involved than that? Thanks, Bill

[billbuilds]

    The pistons arrived back from Fuel Moto today. Jim did a great job machining the dome volume down to about 9.9:1 compression. I figured that equates to a 2.7ccdome volume. The pistons each weight exactly 394.3 grams.
A big thanks to Jamie and Jim at Fuel Moto for the great service.     

[Ohio HD]

The pistons arrived back from Fuel Moto today. Jim did a great job machining the dome volume down to about 9.9:1 compression. I figured that equates to a 2.7ccdome volume. The pistons each weight exactly 394.3 grams.
A big thanks to Jamie and Jim at Fuel Moto for the great service.     

    

[Ohio HD]

If it's my head, I take it down after machining and clean it up. Get two new valve seals and and move forward.

[Buglet]

  Now that you have your pistons back did you gat a chance to install them a check the deck height to see if they are both the same. If they are not then the cylinder would have to get machine so they are even.

[wfolarry]

You're overthinking the .5cc.
You would be lucky to be that close when the engine is assembled.
Put it together & run it.

[billbuilds]

You're overthinking the .5cc.
You would be lucky to be that close when the engine is assembled.
Put it together & run it.

     Thanks, Larry. I was wandering/thinking along those lines as well.

     
     I have not had a chance to check the deck height yet and I do have a question or two there: Installing the pistons  in cylinders w/o the rings, do I need to shim the piston to cylinder wall to get an accurate measurement? I know it should be clean but should cylinder wall be lubricated some too as this time? 

[kd]

For me fitting the piston to the bore with a layer of painter's masking tape before you mount them to the rods works well.  Just snug enough to prevent them from rocking in the bore. Oil will release the glue on the tape so no more the enough to keep the air from causing oxidation should be used (before and after). A clean oily towel should do it but not an oil soaked one.  Do the final scrub and re-oil just before final assembly.

[jsachs1]

For me fitting the piston to the bore with a layer of painter's masking tape before you mount them to the rods works well.  Just snug enough to prevent them from rocking in the bore. Oil will release the glue on the tape so no more the enough to keep the air from causing oxidation should be used (before and after). A clean oily towel should do it but not an oil soaked one.  Do the final scrub and recoil just before final assembly.

When using tape, don't wrap it below the ring lands, and be sure the ends are NOT overlapped when you're finished wrapping.   1/4 " wide tape works best.
John

[kd]

  Also the colored painter tape (as opposed to general masking tape) has less aggressive glue that works well and doesn't leave hard to remove residue.

[Garfield]

    I use the ScotchBlue   

[billbuilds]

     Thanks for the replies. I have both blue and yellow painters tape. a little wide but nothing a pair of long blade scissors won't fix. If it'd just warm to the mid to upper thirties I could work in the garage. Didn't get out of the teens yesterday and at 8:03AM EST it's -3F. Contact cleaner is nasty stuff and I refuse to use it in the house/basement. Supposed to get near 50F Thursday. Tom Petty was right, the waiting is the hardest part. 

[billbuilds]

     The piston pins that I need won't be available to ship from the manufacturer until at least 3/23. Bummer

[Ohio HD]

Bill, I made a post in Marketplace to see if anyone may have ideas as to where you might acquire these.


HTT Marketplace

[billbuilds]

     Thanks Brian,
     I don't recall the supplier that I spoke with yesterday (it wasn't Summit Racing) but he called Diamond to see if they might have a couple kicking around and was told that these are THE most backordered pin that they manufacture. I appreciate your help, Bill