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Discussion Starter · #1 ·
Hello All,

I have a 1980 Honda CM400T and I just took the engine apart to replace all the gaskets. After reassembling the engine, I got to the last portion of tightening down the piston cover bolts. (12 & 10 in the image provided) They require a torque wrench, but I stupidly decided to tighten them without one. Once it hit a certain point, they broke the threading inside where they tighten to and they will no longer tighten. It happened to 2 of 8 bolts. What can I do? Do I need to replace the whole engine?
 

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Your helicoil or time cert would accept 10 X 1.25 standard bolt, else get bigger bolts which will be non standard.

The hole the helicoil or time cert fits into would be bigger than 10 X 1.25 but when fitted, the standard bolts will screw into the helicoil or time cert.

You will need the correct drill and thread "tap" to make the wreaked holes the correct size and thread for the helicoil or time cert, hence the research needed.

Do your research.

Did you clean out the 4 centre head bolt holes before reassembly ?

Did you fit the head bolts into thier proper holes ?

The head bolts are different length.

I wonder what Other problems are going to emerge....
 

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Discussion Starter · #5 ·
Your helicoil or time cert would accept 10 X 1.25 standard bolt, else get bigger bolts which will be non standard.

The hole the helicoil or time cert fits into would be bigger than 10 X 1.25 but when fitted, the standard bolts will screw into the helicoil or time cert.

You will need the correct drill and thread "tap" to make the wreaked holes the correct size and thread for the helicoil or time cert, hence the research needed.

Do your research.

Did you clean out the 4 centre head bolt holes before reassembly ?

Did you fit the head bolts into thier proper holes ?

The head bolts are different length.

I wonder what Other problems are going to emerge....
Yes, I cleaned the whole engine before reassembly. I took pictures before so I knew where to put the bolts back. I definitely put the right bolts back in place, I just simply over tightened and broke the threads in the aluminum base they screw into. I understand the helicoil and timing certs after doing some research on them. Yes, I will just have to make sure I have the correct drill bit and thread tap sizes before drilling and re-tapping. I was 8 bolts away from just reassembling and testing her up. But, like I said, I had no access to a torque wrench to set their proper torque. Stupidity 100% on me. Just was asking around if anyone has also had this problem and their solution. If the helicoils dont work, im assuming im going to have to buy a new engine base?

Really appreciate youre communication and responses though. Have been very helpful!
 

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I'm in UK, no helicoil 10 x1.25 but worth list timesheet that size.

A kit is available from wurth which I believe are in the USA as well.

So many people ruin stuff by not cleaning completely to the bottom of the 4 inner head bolts. I Use a snap on plug tap just for this job.

I have even come across burst holes with half the hole sitting on the sump floor due to silicon sealer being used in that area, and causing the hole to burst.

Maybe farm your repair of the hole to an engineering shop ?

Get a torque wrench.
 

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What size and pitch are the inserts, the size and pitch when fitted ?

You know the size and pitch needed, your bolt size.
 

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I recently rebuilt a 78 CB400tII. The threads had been stripped in one of the holes. I used an EZ Coil repair kit. M10-1.25 2D (20 mm). Worked great. I did not have the special drill bit recommended so just used the next smaller size that I had and took more material out with the tap provided in the kit. I have another thread on this site which showed more pictures of the tear down and rebuild.

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Good on ya Kurt! Leader of the pack!
 

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There is a small possibility that you could use a Left Hand Drill Bit and just turn the broken bolt out...
That being said, you obviously need new bolts too.
I never found the correct bolts (without the sealing sleeve), however, I could find the bolts with the sealing sleeve. I simply replaced the sleeved bolts and cut the sleeve off the old bolts! Make sure none of the bolts have rust on them!
If you need to know where I bought them, just send me a private message.
Hope this helps! (1980 Cm400t)
 
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