Topic: helicoils on cylinder head

[mazingerzeca]

Hello all.
When I was trying to install the camshaft holders on the cylinder head (CB 750F2), I noticed that there were 7 threads in which I had to insert a helicoil, so I took it to the machine shop and they inserted it. But now, I've noticed that when I insert the  bolts (oiled, of course), the helicoils move with the bolt. It looks like the bolt is so tight and the helicoil too loose on the head. I've thought about installing a threaded stud instead a bolt and a nut over the camshaft holders. Any other idea?
Thank you.

[bunghole]

I've only used helicoils twice, so I'm no expert...although they do work well.

I would imagine that the helicoils will spin with the bolt until they bottom out in the hole.  They certainly shouldn't be loose.  Once they bottom out and the bolt is torqued, that will keep them from moving.

[kslrr]

The helicoils should not move at all.  They are held in place by the bottom and top ends of the wire digging into aluminum.  Yours were not installed correctly.  The coils are eather too long or the guy used the wrong tap.

[mazingerzeca]

I've only used helicoils twice, so I'm no expert...although they do work well.

I would imagine that the helicoils will spin with the bolt until they bottom out in the hole.  They certainly shouldn't be loose.  Once they bottom out and the bolt is torqued, that will keep them from moving.

The problem is that in some of the holes (the ones closer to the plug holes on #1 and 4 with the shorter bolts) don't have bottom, and the helicoil would never stop.

[bryanj]

They may not be correct but you can use a stud and nut so you dont keep turning the coil, also you can get something called a "keensert" but that neeeds a 10mm thread for a 6mm bolt

[mazingerzeca]

The helicoils should not move at all.  They are held in place by the bottom and top ends of the wire digging into aluminum.  Yours were not installed correctly.  The coils are eather too long or the guy used the wrong tap.

There was a previous helicoil installed on the hole. Maybe that's the problem.

[HondaMan]

They may not be correct but you can use a stud and nut so you dont keep turning the coil, also you can get something called a "keensert" but that neeeds a 10mm thread for a 6mm bolt

What he said....
The Keenserts beat the tar out of Helicoils in this kind of aluminum.

Option: remove the existing (new) Helicoil (head off, of course) and Green Loctite it into place. IMO, use more than 7 threads, like a new Helicoil or Keensert, in this location.

These long bolts are only supposed to be tightened to 5-7 ft-lbs, but that's not noted in any manuals, only in a long-ago lost Honda service bulletin. I only remember it because of the number of times I've stripped those rocker shaft retainer bolts. Their only purpose: 1) to hold the rocker shaft from falling out on K2-and-earlier heads and 2) hold the rocker towers in place while passing heads down Honda's assembly line on K3-later engines. They don't secure anything in assembled engines, beyond that. Even if they are fully stripped on a K2-earlier head, the cam cover will retain the bolt enough to prevent loss of the rocker shaft (noted in roadracing engines!). However, if they are loose, it creates an oil leak at the head gasket.

[Markcb750]

Properly installed, there is almost no way a Helicoil can "spin". 

I have designed and built high performance machine tools for decades. (for what ever value that adds to my opinion).

 I have helicoils installed on cast iron and aluminum parts to allow bolt systems to be brought to a very high torque.  I find them very valuable where customers without torque wrenches need to repeatedly remove and replace a part.  can't think of one occasion where the Helicoil spun or failed.


Something went wrong...IMHO

[CB750F2]

Mark, I think that the issue is with the bolts and studs that hold the camshaft bearing caps in place not with the bolts that hold the cam towers and rocker shafts in place.
Helicoils should not be loose if inserted correctly. You may need to locktite the inserts in place before you assemble. Also you will need to put some sealant on the bolt/stud threads to prevent oil leaks on to the head fins. Pat

[Markcb750]

"But now, I've noticed that when I insert the  bolts (oiled, of course), the helicoils move with the bolt. "


Sounds like a question about Helicoils, not bolts.


It sounds like too short a insert, or the insert type with a bottom tang was used and the tang /bolt interfered.

Hard to tell from here, well beyond the improperly installed thing.

[mazingerzeca]

"But now, I've noticed that when I insert the  bolts (oiled, of course), the helicoils move with the bolt. "


Sounds like a question about Helicoils, not bolts.


It sounds like too short a insert, or the insert type with a bottom tang was used and the tang /bolt interfered.

Hard to tell from here, well beyond the improperly installed thing.

I broke and retired the bottom tangs. I will try to post some pictures tomorrow, but is difficult to see anything on a picture of a hole. I feel a bit deceptioned with helicoils. Maybe they can work on holes that are closed, but if thy are opened on both sides, they can easily go from one side to the other, logically.