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Post Info TOPIC: Repairing a stripped cam cap thread with a Recoil or Helicoil kit


Super Guru

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Repairing a stripped cam cap thread with a Recoil or Helicoil kit
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Typical - you have just rebuilt your engine, torqued down the head and you are just fitting the camshafts when you strip a thread on a cam cap cry

Sadly there is no way to do a repair that I can see without taking the head off again no

Anyways up, this is a rough "how to". Quite a few of my photos were unusable and, to make the item flow, I have had to use a couple that are rubbish but I hope you get the idea. I am not going back over to take the photos again disbelief

The symptom of a stripped thread is obvious as the bolt won't torque down.

I use a 6mm Recoil kit but other kits are available which will do just as good a job.

Briefly, you need to drill out the damaged thread, tap the hole, thread in a steel insert and you have a thread that is stronger than the original.

This is my kit:

 Helicoil Recoil cam cap thread 1.JPG

Helicoil Recoil cam cap thread 2.JPG

 

You can drill out the hole using the supplied drill bit in a hand-held drill but I have an old pillar drill which comes in handy for just this sort of occasion and gives a better chance of me drilling the hole vertical.

Before drilling, mask off the area to keep the swarf out of the cam buckets etc.

Helicoil Recoil cam cap thread 3.JPG

 

Then tap the hole using the tap provided in the kit and blow out the swarf with an airline or can of compressed air - or simply shake it out.

Helicoil Recoil cam cap thread 4.JPG

 

Next, install new the new thread insert. Use the special tool which engages with a tang on the insert and lets you screw it down into the new thread you have made:

Helicoil Recoil cam cap thread 6.jpg

Helicoil Recoil cam cap thread 7.JPG

 

Next remove the tang by tapping it with the punch and hammer:

Helicoil Recoil cam cap thread 8.JPG

Helicoil Recoil cam cap thread 9.JPG

 

I have a small telescopic magnet which I use to remove the broken tang but it would probably just shake out.

All that is left to do now is to check the bolt screws in and out nicely and job done!

Helicoil Recoil cam cap thread 10.JPG

 

Brian



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Guru

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hi brian i know helicoils are good but dated nowadays timeserts are excellent when fitted right they cannot pull out like a helicoil look them up on the web i have used them some time but not cheap but there agan cheaper than a new head

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Super Guru

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Hi John and welcome to your new well-earned Guru status!

Nearly all the stripped threads I encounter are the common 6mm ones as found in the crankcases etc on the TTR. For these, the Recoil kit is perfect and a cheap repair. Also, being a practical guy, I use what I have wink

As you say, lots of interesting information on the interweb such as here:

I also located a metric bolt torque table from that video and it answered a question I had in my mind as to whether the torque settings used by Mr Yamaha in his workshop manual refer to dry or lubed threads. Looking at the chart, I am pretty sure they are dry settings because, if you look at the M6 torques setting, the nearest to that in the workshop manual is the dry setting i.e. 10Nm. What do you think?

metric bolt torque table.jpg



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that chart is very usefull brian i am going to print it & laminate it may be usefull in the future cheers pal

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Has anyone used a self-tapping version of the helicoil? Head cover on the CB650 disbelief looks like someone tried a helicoil without tapping it previously.  Needs 7.5 fp torque.



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