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Help With Cp Pistons And Bc Stroker Oil Squirter Clearance

HarrisRacing
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HarrisRacing Proficient

HarrisRacing

Posted
Posted

I am putting my engine together this weekend and just discovered a clearance issue with the oil squirters and the bottom of the pistons.

The crank is BC 79mm stroker (2.75L on std bores) and I have a brand new N1 block. The pistons are CP that came with the stroker kit and as you can see from pictures the bottoms of the pistons do not look relieved in the correct location nor are they deep enough for the stroke of the crank. The piston hangs up with approx 15 deg of rotation until BDC each way.

Deck extension at TDC look like they are def stroker pistons so the wrist pin location is correct, just not relieved on the bottom.

Has anyone seen this with this setup? Perhaps they just cut the bottom for the wrong stroke? They also look like they mossed the location relative to the piston by about 10-20 deg.

I have a call in to CP Carillo but I was curious if any builders have seen this?

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HarrisRacing Proficient

HarrisRacing

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  • Author
Posted

Well I decided to relieve the pistons. I can't wait another 2 months on this project. Took some measurements and cut the Pistons. I got my scale out and sanded them until they all weighed the same too. Very very little change to overall weight and I would say it's negligible. bottom end is together.

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GTRPSI Mentor

GTRPSI

Posted
Posted

Still looks a bit shallow to the eye but it cannot be judged from a picture.

Did you take a measurement of the gap to the squiters?

How much room did you allow? More than 1.5mm-2mm?

HarrisRacing Proficient

HarrisRacing

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  • Author
Posted

I used a bit of modeling clay on the skirt of the piston and ran them down. Yes I have about 1mm clearance. I wanted to be able to lose a rod bearing and not break a squirter off.

Thanks for the replies. I was worried that I was the only one and maybe they sent the wrong pistons.

Patrick

HarrisRacing Proficient

HarrisRacing

Posted
  • Author
Posted (edited)

modeling clay showed me where to cut. Then I made several cuts on the first one and kept checking. Once I got that one done, I measured from top of piston with calipers and cut the rest. It was directly inline with one of the oiling holes for the rings, so alignment was easy. I still think I barely missed the angle, but they all have adequate clearance.

Plus the rods grow when they get hot, and yes the piston grows down on the skirt, but only from the wrist-pin down. I can run calcs, but I'm betting nothing will touch.

Patrick.

Edited by HarrisRacing
HarrisRacing Proficient

HarrisRacing

Posted
  • Author
Posted

Oh and they are cut at an angle about 20 deg from horizontal plunging in from the outside to the inside. This is why they look shallow. They follow the angle of the squirters.

Kinkstaah Grand Master

Kinkstaah

Posted
Posted

I have the same kit in my RB25Neo.

Can confirm you need to do something about the squirters. I'm no engine builder but I believe they came to the same conclusion you did, and modded the pistons with a relief.

The previous engine builder opted to just remove the squirters.

:/

GTRPSI Mentor

GTRPSI

Posted
Posted

40 thou may not be enough.

Firstly when checking with modeling clay, remember your pushing the piston over (rocking it over) with the clay, where as you really should be rocking it the other way into the squirter for the true minimum possible.

Then allow for bore and piston wear which will let it rock over further.

Id be aiming for a minimum of 80 thou (2mm) +.

You also have the option of putting washers under the squirters should you need a little more if its already assembled.......not too much as remember they are positioned by the pin holes.

Just remember more clearance is better than less.

From memory stock pistons have quite a large cutout to clear the squirters so dont be scared to take out more than you need.

Borci88 Veteran

Borci88

Posted
Posted

I have the same kit in my RB25Neo.

Can confirm you need to do something about the squirters. I'm no engine builder but I believe they came to the same conclusion you did, and modded the pistons with a relief.

The previous engine builder opted to just remove the squirters.

:/

That's because you don't need them with Forged Pistons like you do with Cast.

Kinkstaah Grand Master

Kinkstaah

Posted
Posted

That's because you don't need them with Forged Pistons like you do with Cast.

That is what the first builders said

wat

This is what the second builders said

HarrisRacing Proficient

HarrisRacing

Posted
  • Author
Posted

Well you got me paranoid so I added some copper crush washers under the squirters today. Just that extra bit of insurance.

Note for future builders , clearance more than my pictures just in case

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  • 4 months later...
HarrisRacing Proficient

HarrisRacing

Posted
  • Author
Posted

FYI you shouldn't have to worry about this any longer. I called CP and they are opening discussions with BC about these pistons. Said they totally see the crash after comparing them with other RB26dett custom pistons and considering stroke looks like it was overlooked somewhere somehow.

You're welcome whoever you are...

And for the record. The BC stroker 8.5:1 CR pistons with valve reliefs are 15.77cc of added dome...Need to take that into account if cutting head, running thin head gasket, etc. I think it's about 8.62:1 if running stock bores on a 1mm thick head gasket, and stock 70cc's in the head.

Patrick

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