Perkins 4108 injector bolt thread

Roberto

Roberto

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Hello,
I discovered one of my injectors had one loose bolt (the two bolts that keep the flange tied to the engine), there was some tiny though noticeable amount of smoke coming from the area. The opposing bolt seems ok.
I tried to tighten the bolt and the smoke went away, though the flange was still a bit inclined, I tightened more and obviously something in the thread was stripped: the bolt turns both ways but does not move up or down, I don't know if I broke the bolt thread or the female thread inside the engine. Now more smoke and definitely more noise.
Anyway, I'd like to prepare for both occurrences, buy a couple of new bolts and an helicoil (I'll be back to the boat in a few weeks).
The bolt head is 1/2", what type of thread is it? UNC maybe? Also, how long is it?
Re Helicoils: the size they indicate is the one of the thread that must be replaced? Shall I buy 1\2" helicoils?
Final question, the bolt is in an awkward position I could not check: is there enough metal to use an helicoil or is there the risk to damage the injector housing or even combustion chamber. FWIW it is the first bolt of the first injector, the water pump side of the engine.

Thanks
 
You usually buy a helicoil which is the same as the thread that is stripped and which you want to re-create.

The helicoil itself will obviously be a bigger thread so you need to make sure that you use the drill and tap which are correct for that helicoil. If you buy a kit, it will contain the correct drill bit and tap.

Helicoils are usually a standard length and will be around 1/2 inch. If you are referring to the 1/2 inch head then that is not what you need to size the helicoil. You need thread size and pitch to size it, presumably imperial for a 1/2 inch head - 5/16 BSF/BSW or UNF/UNC or whatever.

Richard
 
Last edited:
If the hexagon really is 1/2", that indicates a unified thread, 5/16" unc or unf, likely on elderly UK engines. Note however, that's pretty close to 13 mm which would be an M8 thread. BSF or BSW would be slightly larger. However, with some engines, hex size isn't necessarily standard. Best remove a bolt and measure it.
Edit, beaten to it, definitive answer above.
 
Thank you both, very informative!

(I bought helicoils kits for a lot of metric sizes but never used them yet. Of course the first time I need them they have to be imperial :) )

Ah another question: I have a Bowman exchanger, the second bolt of the same first injector is quite difficult to reach with wrench, socket or whatever. I figured to remove all the other injectors, this would give easy access to that second bolt.
It might be the occasion to check the compressions, though it's a lot of work: is there any way of unscrewing that second bolt? Cut/shorten a 1/2" wrench maybe?

regards
 
earlybird said:
If the hexagon really is 1/2", that indicates a unified thread, 5/16" unc or unf, likely on elderly UK engines. Note however, that's pretty close to 13 mm which would be an M8 thread. BSF or BSW would be slightly larger. However, with some engines, hex size isn't necessarily standard. Best remove a bolt and measure it.
Edit, beaten to it, definitive answer above.
Click to expand...

thank you, as said by pcatteral it is 5/16", the head would not fit into a 12metric and the 13 metric is somehow loose, the 1/2" fits perfectly.
I'll try to source 5/16" bolts in the various threads if possible.
rgds.
 
RichardS said:
Sometimes I think I must have already passed on. :o

Richard
Click to expand...

Before you do you might like to go back to #2 and edit the reference to "BSC", British Standard Cycle , thread. I'm sure you must have meant BSW, British Standard Whitworth. :)
 
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