Making the CompCams piston stop work.

[99COBRA2881]

During the process of putting together my DOHC race motor, I was ready to check piston to valve clearance but the CompCams 14mm piston stop wouldn't engage the threads in the spark plug hole.

COMP Cams 4795 - COMP Cams Piston Stop Tools - Overview - SummitRacing.com

I posted here about this problem and was told the tool "needs to be modified to work". I knew this meant material was going to need to be ground off. I didn't grab my grinder instead I chucked the piston stop up in my bench top metal lathe and removed about .035" of material off the shank.

The CompCams piston stop works great now and it wasn't worked over with a grinder. The threads are all still in perfect condition.

My question is would anyone be interested in a modified piston stop? The stop sells for $8.25 from Summit, after being cut down I would sell it for $10.25+ shipping. You pay two dollars and get a stop that works right out of the box.

Shipping would be $5.40
Total $15.65 Shipped!!!

Arrow points to area that was turned down.

Thank you,
Anthony
Midcontinent Mustangs
(785)658-5921

 

[MrBrain]

The upper part is originally designed as a spark plug, how doesn't this work as is? Does our cars only use the lowest parts of the threads, as the real plugs threads are twice the length?

 

[99COBRA2881]

The shank above the threads prevents the piston stop tool from engaging the threads in the spark plug hole. As cast the piston stop sits and spins in the spark plug hole. Once the shank is removed then it can drop lower to engage the threads.

 

[MrBrain]

Yes, this is what sound so strange to me. I understand that this have to be done, but are our heads this wierd for real? Doesn't this basically mean that threads in the head doesn't go all the way up to the shank of the spark plug?

No wonder people are shooting plugs through the cops.

 

[99COBRA2881]

Correct, I'll get a pic with the heads off that shows all four threads in the spark plug hole. Heads are C heads.

 

[MrBrain]

Dear god! Is there a reason that Ford have it this way then? I hardly think someone designed it this way because he's just dumb...

 

[Tabres]

Bummer. Wish this had come up sooner. I just last week bought a Comp piston stop, knowing I'd have to modify it.

 

[99COBRA2881]

Bummer. Wish this had come up sooner. I just last week bought a Comp piston stop, knowing I'd have to modify it.

Imagine my suprise and frustration of not knowing the @*#&!!#& piston stop wouldn't work as is out of the box!! I had to find out the hard way!!

 

[na svt]

You can buy a piston stop that works, if you know what to look for. You can also remove the ceramic from a plug, tap it with a 3/8 tap and use an extra long 3/8 bolt as the stop. I weld a plug socket onto the modified plug and the result is an easy to use piston stop. Oh, and I round the end of the bolt to remove any sharp edges that could damage the piston.

Oh, you can also just weld a 1" rod to the bottom of a spark plug and it will do the same thing.

 

[99COBRA2881]

You can buy a piston stop that works, if you know what to look for. You can also remove the ceramic from a plug, tap it with a 3/8 tap and use an extra long 3/8 bolt as the stop. I weld a plug socket onto the modified plug and the result is an easy to use piston stop. Oh, and I round the end of the bolt to remove any sharp edges that could damage the piston.

Oh, you can also just weld a 1" rod to the bottom of a spark plug and it will do the same thing.

Many people don't have a welder or a tap and die set. The cost to buy just a 3/8" tap and the long 3/8" bolt( not to mention the time involved modifying a spark plug) will cost more than the $2.00 I charge for modifying the CompCams stop. ;-)

 

[na svt]

Many people don't have a welder or a tap and die set. The cost to buy just a 3/8" tap and the long 3/8" bolt( not to mention the time involved modifying a spark plug) will cost more than the $2.00 I charge for modifying the CompCams stop. ;-)

very true