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Helicoil for stripped threads in block due to head stud not properly seated?


RSL

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Right cylinder just recently started making noise, diagnosed as loose head stud nut(s).

 

Per Clymer, I loosened the four head stud nuts, then criss-cross torqued to 20 NM, the another 90 degrees, then final 90 degrees. On final turn of the lower front stud nut, she let go.

 

I should have noticed that this stud had more threads showing above the nut than the other studs. This was because this stud was not properly seated into the block in the first place, perhaps due to "maintence" during prior ownership. When removed, this stud had aluminum from the block clogging the lower 1/2 of the threads, whereas the upper half of threads were virgin. So, the stud was not properly seated in the first place, and only half of the threads were gripping.

 

What to do? The cylinder must be removed to install Helicoil or similar into the block so the stud can get full grip. Is this difficult, risky, or expensive?

 

How best to proceed?

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I haven't heard of this being a problem on the oilhead engines, but the subject comes up all the time on the /5 forum. The consensus is that for this application Heli-Coils are a bad choice, and I can vouch for that. Time-Sert is one product that provides a more robust repair:

Time-Sert FAQ

Hope that someone will chime in with actual experience with oilhead stud repair.

Peter '73 R75/5, '04 R1150RA

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I realize you asked for oilhead input; but fought this for about 40k miles on '95 Airhead. I did all the recommended fixes: end play,re-torque,c-clamps, etc. My cylinder studs were pulling out of block just enough to loosen valves(exhaust) in my case on right side. I installed Heli-coils and did not have to adjust valves for next 26k miles until totalled. I do not know torque value of oilheads but Heli-coils were well within Airhead value.

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I had the same issue on my R1100RS. Not that common, but it happens, usually caused by severe over-heating.

 

As some of you know I have a jinxed bike. It's OK, I know it is, but I love it anyhow. My R1100RS has had a fairly serious leak for the last 5000 miles or so. I guess my bike really wanted to make sure I know the real meaning of OIL HEAD! The head is covered in oil, or was.

 

My left cylinder has had a leak off and on for a while. Its cause took some time to figure out. But when I went to retorque the head gasket I found it. The lower left (front) head stud had pulled out of the case. This made it unable to hold torque, or oil for that matter.

 

Here are a few pictures on what we had to do to fix it.

 

We went over to Anton's house to take advantage of his tools, knowledge, and as it turned out, his hospitality.

 

Anton was great, as was Meredith!

 

Here is a picture of my bike partially disassembled in Anton's shop.

 

A-Open-engine-02.jpg

 

This picture shows the head, cylinder and piston removed. It also shows the offending stud hole after I pulled out the stud. (Lower left hole)

 

A-Open-engine-01.jpg

 

The hole, with gummed up threads.

 

A-Stripped-threads2.jpg

 

It turned out that the previous mechanic had already heli-coiled this hole. My guess is they screwed it up. The threads of the bolt were chewed up. If the heli-coil had been done correctly the bolt should have been fine and the heli-coil would have held. It was our contention that the heli-coil and bolt cross threaded. Morton's BMW did the head gaskets just before I purchased the bike. Though, in fairness, it may have been done before that even.

 

We removed the old heli-coil, chassed the threads and added a new heli-coil and bolt. I have to say that I was very nervous retorquing the head, and when I got to the offending stud, last of course, I only gave it the recommended torque and 90 degrees turn instead of the book stated 180 degrees. All the others went 180. I was to scared to do 180, reasoning that the oil passage would hold at 90. For the record Anton said to go 180, but I couldn’t. Flame away.

 

You can see what 5K miles worth of leaking Mobile 1 does to a hot cat and muffler.

 

A-Oil-mess-01.jpg

 

In this shot you can see the carbon buildup on the head, and the piston had more. It appeared like it was mostly burned oil, but I don't know for sure.

 

A-head.jpg

 

The arrows show where the oil was leaking because of a lack of torque on the head bolt. Fortunately the other three head bolts form a near triangle over the cylinder ensuring good compression.

 

This picture shows the cylinder cleaned up with the piston stuck in it just up to the bottom oil ring. This was less than half an inch into the cylinder.

 

A-piston-and-cyl.jpg

 

Notice the size of the piston? Hardly any skirt at all.

 

We reassembled it and changed the oil. No major problems except me mixing up a few of the bolts and burning myself on hot oil.

 

After words I test rode it, and then did a TB sync.

 

That was yesterday. Last night we went to an ADV Rider party with Anton and Meredith and then stayed over at his house! They are great hosts and I really appreciated their hospitality.

 

Best yet, Anton charged me a VERY fair rate to help me and provide the cylinder stud and location to work!

 

Jim cool.gif

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I haven't heard of this being a problem on the oilhead engines, but the subject comes up all the time on the /5 forum. The consensus is that for this application Heli-Coils are a bad choice, and I can vouch for that. Time-Sert is one product that provides a more robust repair:

Time-Sert FAQ

Hope that someone will chime in with actual experience with oilhead stud repair.

Peter '73 R75/5, '04 R1150RA

I haven't done this particular repair on a beemer. I have installed hundreds of time-serts, and thousands of heli-coils (did most of these in aerospace applications). IMHO, the differences between the 2 systems are minimal. Each has it's own benefits. Did you know you can use the same tap - for both systems? This might tell you something..... cool.gif Useful info. I have both systems in my shop right now.

 

all the best,

 

Mike

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