valve cover nut

I know I've seen this in the forum before but can't find it now. Anyone had experience with chrome valve cover nut that will not tighten. Have not had bike long and decided to do a valve adjustment and noticed chrome valve cover nut missing. Ordered new one and did valve adjustment. New one arrived and it will not tighten. HELP!

I don't have the final answer for you, but some details to start. The chrome nut screws onto a stud that I believe is pressed into cylinder head. Are the threads on that stud stripped? If so, you might get away with retapping the stud. Or the stud itself might be loose in the head, just spinning in the hole. Greater experts than me will have the right answer for securing the stud, would red Loctite suffice? I have always been real gentle tightening mine, I have read it is the easiest fitting on the bike to mess up, I think because the stud comes loose from the head. First step would be to remove the valve cover again and have a good look at the stud, try and thread the chrome nut on without the cover to see what the problem is.

The threads in the head are probably stripped (it doesn't take much). Installing a helicoil is a good solution though some use a thin nut with a longer stud. If you look down through the fins, it'll become obvious where the nut goes. I used a helicoil to repair mine. Good luck.

Helicoils in the old airheads are almost a knee-jerk.

Got lots of airhead buddies? Ask around, one of them has bought the 8mm set you need- this is a very common failure.

Lots of people have this problem because the threads in the head are stripped.

The stud is indeed screwed--not pressed--into the head.

BMW fitted lots of these that were too short, exacerbating the problem.

If I recall correctly, torque setting for these nuts are only about 16 ft. lbs. Do not forget to re-install washer! Too much force has resulted in problems such as you describe.

I just found out the same thing, nut just spins. I used a bit of gasket sealer to short tem solve my problem. Short term, until this winter. Please keep us posted on what you do to solve the poblem. I'll be looking for the thread!!!

Really, you don't even need the chrome nut, as the two side nuts will hold the valve cover sufficiently.

The center valve cover nut should be installed with only a little more torque than you would use with your fingers. It requires almost no force to hold the valve cover gasket's seal, and in the future you won't have that problem again. There is a previous thread where it was shown how to replace the stud with threaded rod and nut, where the nut was ground down and placed on the back side of the head where the hole passes through (the hole is drilled and tapped all the way through the head).

valve nut repair

Wasn't as bad as I thought it would be. Stud pulled threads from head. Drilled out hole with 7/16" bit being careful to cover pushrod holes, cleaned up mess and installed a GARD 8mm insert, worked like a charm. Problem solved.
Back on the road in less than an hour.

Thread pitch

Does anyone know the thread pitch to the stud. Or, could someone post a link to the helicoil product mentioned for this M8x70 stud, thanks.

My guess is that the pitch is a coarse thread. The stand pitch for a coarse thread M8 bolt is 1.25. A fine M8 is 1.00.

http://www.zerofast.com/threadm.htm

pszyjka said:

Does anyone know the thread pitch to the stud. Or, could someone post a link to the helicoil product mentioned for this M8x70 stud, thanks.

Click to expand...

Here is a source for heli-coils. You will need the Kit with the insertion tool, and the proper tap, on right side of page. Each kit is supplied with the proper drill, proper helicoil tap, and several of size (length) of inserts, or a several sizes (lengths) in some cases.

http://www.mcmaster.com/#helicoils/=qdqzmr

Inserts with tool include a plug tap, installation tool, and drill bit (unless noted).

It appears that the only length they have is 12mm if proper size is 8 x 1.0 finer thread, but yours probably had coarse theread . . .

It appears that the length sizes for the coarser 1.25 pitch are 8, 12,16 in one kit, and 12 in the other kit.

Procedure is to:

1. drill out existing hole using special helicoil sized drill

2. hand tap with helicoil supplied tap

3. Using insert tool, put proper length insert on tool (with break-away tab on bottom - goes into hole first), and "screw" it into the previously threaded hole. It will "stretch" (kind of like a slinky) as it screws down and follow the thread that the previous tap made. When fully down so it is flush with top, back off tool and the break-away tab will break off as it is supposed to do. That is why you want to get insert down as much as you want. Once tab breaks off, there is no screwing it down further. If for some reason it doesn't get down far enough. It is pretty easy to get back out but it will no longer be usable. Using a pair of needle nose pliers, grab the top thread and pull up, the thread will uncoil up out of the hole. That insert is no longer usable.

Using another insert from the kit, repeat process until you do get it right. You may have to use a shorter insert if longer one won't go down far enough.

Some of our customer's engineers actually designed stuff with inserts in them from the beginning, because the inserts are stainless. And according to some I have talked with, they are actually stronger than original threads were - especially in aluminum.

pszyjka said:

Does anyone know the thread pitch to the stud. Or, could someone post a link to the helicoil product mentioned for this M8x70 stud, thanks.

Click to expand...

If you check the thread pitch on the stud, using a scale (measuring tool like a ruler), if it were 1.0 pitch, it would measure around .040 (about 2/3 of 1/16"). If it is coarse pitch (as I think it is), it will measure just under 1/16" !.25 mm is about .050 in thousandths.

One way to be sure is to take a known nut and try to screw it on the stud. I would take stud with me to good hardware store and try both 8mm pitch sizes. That way you will be sure to purchase the correct pitch size helicoil kit.

It's quite easy to determine the pitch of the stud...best to use a metric ruler, though...I'm getting better at metric the more I use it!! For metric threads, the value is mm per thread. For SAE it's threads per inch. Kind of different there.

Simply measure the metric distance between say 10 threads (actually it's from the first thread to the 11th thread...you're trying to measure 10 gaps) and divide by 10. It'll be pretty obvious if the pitch is 1.0 mm per thread or 1.25 mm per thread.

But the best way, as suggested, is to go to the hardware store and try the stud in a number of nuts from the various drawers or the sample rack they usually have on display.

20774 said:

It's quite easy to determine the pitch of the stud...best to use a metric ruler, though...I'm getting better at metric the more I use it!! For metric threads, the value is mm per thread. For SAE it's threads per inch. Kind of different there.

Simply measure the metric distance between say 10 threads (actually it's from the first thread to the 11th thread...you're trying to measure 10 gaps) and divide by 10. It'll be pretty obvious if the pitch is 1.0 mm per thread or 1.25 mm per thread.

But the best way, as suggested, is to go to the hardware store and try the stud in a number of nuts from the various drawers or the sample rack they usually have on display.

Click to expand...

Excellent method - it is always better to measure a known (longer) distance (10 is perfect) and then calculating down to 1.

Over the years, teaching the machine trades to apprentices, the confusion about thread nomenclature has existed between metric and English making it more difficult for people to sort out.

Metric threads (for example. 8mm x 1.0) means 8mm diameter with a pitch of 1mm distance between threads. This is the textbook definition of the word "pitch." The higher the pitch number the COARSER the threads as explained on chart by Kurt earlier.

However, along comes the English!

English (American) nomenclature for threads goes like this: (example. 1/4-20) This means 1/4" diameter. However, the English measurement doesn't measure true pitch! The "20" part of this designator actually refers to the number of threads per inch! Here, the higher the number means a FINER pitch. In the English method, to get the actual pitch (textbook definition of "pitch,") you must take 1" and divide by the number of threads (in my example, "20") to get actual pitch! 20 divided by 1 = .05 - actual distance from one thread to next.

The textbook def. of "pitch" is "the distance from one feature of thread profile (like valley, or crown) to the same feature on the next thread." This def. goes along perfectly with the Metric method of thread designation. However, when using the English method you still have to do some calculating to get the actual per-thread pitch!

I gets even more confusing when one gets involved with multiple threads on a bolt.

stripped

I used to grind down an 8mm nut to put down in the back of the head and make a longer stud to reach it but that was a real PITA to take on and off for valve adjustments. Helicoils are ok but I got a box of metric Timserts off ebay. 8 x 1.25 is the size. drill it out to 10mm I think and tap it to 1 x 1.25 (might be 1.50) run the Timesert in and Bob's your uncle.
I don't know if I ever saw a worse design than that chrome nut, stud set up for the valve cover. I think we all have had a weepy valve cover and decided to give the nut a little torque and the got that sick feeling when the nut went spinning.

Thanks again for the info. This forum is an endless wealth of knowledge.

Silicone Valve Cover Gaskets?

I have an 85 R80 and when the bike was new and I was young and foolish, I would take the bike to the dealer for service and then notice that the left valve cover was drooling oil. I would tighten the nuts until the drooling stopped. You can probably guess how that turned out.

Later, I heard (don't know if this is true) that airheads of my era tended to suffer from slightly warped heads on the left side.

So, I switched to silicone rocker cover gaskets and the leaking stopped. The silicone gaskets are a floppy pain compared to the OEM paper gaskets, but you don't need much torque on the cover nuts to keep the oil inside. I guess that the thick, squishy gaskets can make up for a little warpage.