Piston Stops

Clayon

Clayon

#1
#1
Okay, I have a question that may sound dumb but what are piston stops like in the picture below used for? are they used to lock the motor so a flywheel can be removed, etc. ? or would that scuff up the top of the piston?



Thanks for the help, it sound like something I should know by now but I don't. :doah:


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massacre

massacre

#2
#2
On V8 engines I use a piston stop when I'm timing cams, when I am finding TDC of the crank. I have also used it when changing valve seals with the heads on the motor, it keeps the compressed air from turning the engine over.
I assume that a piston stop could be used similarly on a single-cylinder engine?

I like what you said about holding the crank so that a flywheel can be unbolted, that makes total sense. My piston stop has a brass end though so the piston doesn't get damaged.
 
KustomKartKid

KustomKartKid

Administrator
#3
#3
As stated above, used to find TDC. You need to use it with a degree wheel bolted to the crank and a fixed pointer. Turn the motor slowly in one direction unitl it just bumps the stop..note the position on the degree wheel...thenturn it back the opposite direction and do the same.

Now with the tool removed rotate the motor to the number exactly in the center of the two points previously noted = TDC.

I would use the rope trick to lock up a motor...that plug tool could leave a mark in the piston which might become a hot spot for detonation.
 
Clayon

Clayon

#4
#4
Thanks Massacre and Gerry for answering my question. :thumbsup: Makes sense, and the brass end is a good idea. Thanks again.


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massacre

massacre

#6
#6
Do a lot of people degree the cam in these motors?
Do you guys set up a dial indicator on the valve spring retainer and everything to set the intake centerline? Or are you guys more checking the lift/duration of a reground cam just to check the specs?
I know that advancing the intake centerline is supposed to lower the powerband and promote torque production, while retarding the cam is supposed to add more top end.
Just curious as to how deep people get into this, thanks!
 
65ShelbyClone

65ShelbyClone

Well-Known Member
#7
#7
I doubt that most members here are actually verifying the cam events and then making adjustments since most cams aren't adjustable without twisting the crank gear.

I used a piston stop to find actual TDC for lining up a timing tape I made and for aligning a 36-1 crank trigger wheel for digital ignition. It's satisfying to see a rock-solid timing number on the flywheel that exactly matches commanded timing on the laptop. :thumbsup:

I also plotted the stock cam lift curve with a dial indicator so I had a baseline to use for some software simulation.
 
massacre

massacre

#8
#8
True, I didn't know if people advanced a tooth or retarded a tooth to change the cam timing. I guess it depends how many degrees 1 tooth is lol
 
65ShelbyClone

65ShelbyClone

Well-Known Member
#10
#10
There are 29 teeth on the 340/390 crank gear.

360 ÷ 29 = 12.4° per tooth, which is going to be way too much in anything but a very unusual situation.
 
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