CTR Pistons in B17 - Build Problems

ASSISTANCE Hybrids & Advanced Aftermarket Engine Performance
1

Looking down into the spark plug hole. What you see is the top of the piston at TDC.

Seeing this, I put a section of vacuum hose onto a pick and rested the hose against the top of the shelf that the spark plug would sit on and inserted the pick until it bottomed out against the top of the piston. I placed the pick next to the spark plug and as you can see, there’s not a whole lot of room between the top of the piston and the sparkplug.

Is this possibly correct? I know there are a couple other people out there with CTR pistons in a B17. Can you shed some light?

B17a crank and rods with oversized PCT pistons and OEM head gasket.

2

Also, the block was decked .005" because it was warped. The head was also milled a bit (to ensure a flat surface).

Lets say there is supposed to be .006" more clearance, that still isn’t a whole lot.

3

Duy… how much was the head milled?

4

I don’t see that as a problem. You still have quite a bit of clearance.

5

if its milled enough it will be.

6

.050"

7

The block was decked 50 thousandths. I’m not sure how much the head was milled but the clearance seems aufully close.

8

Why? The picture shows exactly how much clearance there is between the tip of the plug and the top of the piston with the milled head installed as it would be when the car is running.

It looks like you have about 1/16" of clearance, I dont think you have anything to worry about.

9

Damn… is that what 11.4 to 1 compression looks like… or is your cr higher now…

10

did you install the pistons with the motor in the car?

11

I’m thinking the compression is way over 11.4

As for the other question:
http://www.phase-shift.net/phasedocs/projects/Automotive/B17a_01.htm

12

Duy,
is Schu Right in saying .050 for the block? And arw321 u’d seriously trust a pick and rubber hose to determine valve to piston clearance? glad you’re not building my motor.

13

I could be way off on this, but… If you can use clay for valve to piston clearance, then why can’t you use it for piston dome to plug clearance?

I don’t have the specs in front of me, but there has to be enough clearance to allow for rod stretch. Awhile back I was reading posts from a well known engine guru on H-T, and he didn’t recommend using PCT pistons in anything but a B16B. His recommendation was JDM B16 P30 pistons with different thickness head gaskets / head & block decking to achieve good compression and clearance.

14

Robbie, as I said, the block was milled 50 Thousandths of an inch.

15

Bump

16

Damn dood, that is hella close, too close for comfort.

17

:lol: how about adding a washer to the plug or changing plugs entirely. might change the burn/heat dissipation characteristics tho. or you can take me to pickup my dial indicator i bought and depth gauge. :stuck_out_tongue:

18

Lol.
Of course I was basing what I said on the assumption that the measurements were accurate.

And we aren’t talking about piston to valve clearance here.

I have an LS block with CTR pistons and when I clayed my motor I used a piece of clay to also check piston to spark plug clearance, and I probably have just about as much clearance as Archon has.

CTR pistons have huge domes. Of course the clearances are going to be tight.

19

My .25mm over PCT pistons work fine in my b18c1, but then I didnt mill the head or deck the block and I got that extra .030" deck height…

Other than that, it looks fine to me. Fire that sucker up and hope that one of your rod bearings doesnt go.

Later,
BR

20

10mm deck height difference is huge…