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Glow plug thread size

3K views 8 replies 7 participants last post by  PC WIZ 
#1 ·
Hi all, I need to get a flywheel off a nitro marine engine and want to buy a bolt to thread into the glow plug hole as a stopper. I know they are 1/4" dia. and 32 threads per inch, so what bolt should I get off the shelf at the hardware shop? Is it UNF?
 
#2 ·
take the plug with you and get them to match the thread they should have the tool to do it thats how i get bolts that i need
 
#3 · (Edited)
Not sure if its unf. 1/4 is 28 tpi for unf. I think its "unef" but i doubt many places would carry a bolt that size. Bit oddball.
Use something in the exhaust port to stop the piston moving up, something soft as not to damage the piston or port.
 
#4 ·
1/4-32 is Unified National Extra Fine (UNEF), you will not get one over the counter or off the shelf. I used to use some 3/16 cord fitted in the cylinder through the glow plug hole, just have the piston down and feed a heap through the plug hole then wind over and it will stop the piston from going over TDC.

Cheers
 
#6 ·
i use a cable tie in a pinch, with a little bit of soft cloth wrapped around it to make it a bit softer, just make sure your not to rough as the sleeve can cut the cable tie and if it gets through the intake port youll have to strip the motor to get it out.
 
#7 ·
Actually i do that to get the sleeve out, if i need to get the flywheel off i remove the cooling head and turn the piston to BDC and then jam the appropriare sized finger or thumb down the bore and hold the piston. Thats if a couple of taps from a pair of pliers slid down either side of the block with a pair of pliers doesnt loosen it. If its the nut your trying to loosen, wrap a rag around the flywheel and hold it with a pair of vice grips just tight enough that you dont damage it.

Sent from my LG-P705 using Tapatalk
 
#8 ·
In a case like this....just buy the proper piston stop, it wont be the only time you need to use it
 
#9 · (Edited)
The flywheel is actually free spinning, it's just the Universal cup I need to get of the crankshaft, so I can put a new collar under the flywheel. I think a piece of clean wood in the exhaust or the cord down the plug hole sounds worth a go. If not the right tool will do. lol

Thanks fellas.
 
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