Nut thread dia/pitch Eng Mtg Bolt?

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Bicycle Motor Fun

New Member
Gentlement;

On my very first test run with my new 2-stroke, 66cc China Girl engine, I lost two of the four nuts that secure the engine to the frame. Can someone tell me what the thread pitch is for the studs that go into the engine at the mounting positions, the diameter appears to be 6 mm. I would like to obtain a tap and make my own nuts with safety wiring provisions in them to cure the problem. Thanks guys.
 
The studs themselves are known to break easy, too. You might want to upgrade them with higher grade steel before you continue.
 
Thanks guys, especially Rohmell for his tip on Harbor Freight; yup Rohmell, I do have a HF nearby, I'll get over there tomorrow. That way, I can use one of the taps to positively I.D. the thread in the nut that I have. I have a 6 x 1 tap and that is not the thread; it is finer. With the correct thread, I can make new studs using a better grade of steel and I will buy a HS steel quality die for that job! I'll probably make four new nuts, a bit larger in diameter and drill them for safety wiring--then they will never come off!
Thanks again guys. dance1
 
BTW, that Harbor Freight tap and die set also has a pitch gauge for measuring threads, comes in real handy with sizing up random bolts found in the junk box.
 
Thanks again Rohmell; Yup, I went right over to Harbor Freight and picked up that 40pc die set on sale, cost me $9.59! I get home, and now I don't know what I did with the nut that I wanted to gauge! :-||I have one more (two of the four were lost in my first ride) and it is on the engine, 70 miles North of here is where I have the bike at my son's farm. Now Rohmell, what the heck did I do with that one nut? Once I gauge it, I can make more in my lathe. If I don't run across it here, I'll just have to wait until I get up North next week. Rats!
 
You know, I walked right by the hardware display at HF and didn't even think about that metric hardware assortment! This will give me an excuse to go back to HF Saturday and spend somemore $$! Thanks for the tip Rohmell.
 
Yup, you guys are correct; the subject question that I posted on the 66cc engine to frame mounting bolds, are indeed, 6mm x 1. The assortment that I was able to get at Harbor Freight worked out perfectly. Thanks again guys!
 
vincent713 said:
My question is how the heck does the engine mount nuts fall out?? Did you not tighten it?
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Torque on the nuts (6mm studs) should be 50 to 70 INCH pounds. That being said, I recommend replacing all the studs with a Grade 8.8 and using locking nuts. Oh and 8mm stud nuts 150 to 175 INCH pounds.
 
Apparently guys, I did not get the nuts on the four engine studs that mount to the bicycle frame, tight enough. I have read on these pages, that the studs are weak, and should be replaced with 8mm diameter ones as said here. Therefore, I was careful in tightning them. When I completed this bike build, I was excited to go out for my first ride and it was so much fun, I ended up riding about 3 miles! When I returned, the engine was about ready to fall off! I was lucky to get back when I did. brnot

Now with winter here now in Michigan, I think I will take the advise given here to replace those studs with 8mm ones. I checked my local Wholesale Tool supply store and they do not have any metric threaded rod, just SAE. So fellas, where do you get your metric threaded rod from?

Thanks as always, Karl
 
Bicycle Motor Fun said:
Apparently guys, I did not get the nuts on the four engine studs that mount to the bicycle frame, tight enough. I have read on these pages, that the studs are weak, and should be replaced with 8mm diameter ones as said here. Therefore, I was careful in tightning them. When I completed this bike build, I was excited to go out for my first ride and it was so much fun, I ended up riding about 3 miles! When I returned, the engine was about ready to fall off! I was lucky to get back when I did. brnot

Now with winter here now in Michigan, I think I will take the advise given here to replace those studs with 8mm ones. I checked my local Wholesale Tool supply store and they do not have any metric threaded rod, just SAE. So fellas, where do you get your metric threaded rod from?

Thanks as always, Karl
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NO.... the engine mounts are 6mm
 
rohmell said:
If there is a Harbor Freight Tools store near you check this out:

40 Piece Metric Carbon Steel Tap and Die Set

It's on sale now for $11.99, use a 20% off coupon and your cost is $9.59

Also has the M8x1.0 and M8x1.25 tap and dies for chasing the threads on the cylinder head studs.
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-WARNING- ​

Don't buy cheap taps and dies...there's a reason why they're cheap! Yes, they're hard steel but VERY, VERY brittle.

Imagine tapping a hole and the tap snaps off. You can't just drill out the tap because the tap is harder than the surrounding metal and your drill will go off center and really screw things up. Whatever money you saved buying cheap taps will be spent buying the tool you'll need to extract it. Cheap dies go dull fast if they don't crack in half first.
 
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Maxvision said:
-WARNING- ​

Don't buy cheap taps and dies...there's a reason why they're cheap! Yes, they're hard steel but VERY, VERY brittle.

Imagine tapping a hole and the tap snaps off. You can't just drill out the tap because the tap is harder than the surrounding metal and your drill will go off center and really screw things up. Whatever money you saved buying cheap taps will be spent buying the tool you'll need to extract it. Cheap dies go dull fast if they don't crack in half first.
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Correct...and you can buy the size you need. I have a cheap tap and die set..only use the dies, and bought good taps...I have a 6mm and 8mm and that's about all you need unless you have a 8mm X 1.0 thread. Just think how much a good tap cost vs a broken tap in a hole. Believe me, I broke a cheap tap off years ago. Thank goodness the project didn't cost much to replace. Before using a tap, please read up on the correct way to use it. You don't just screw the tap in and cut threads, and use a lubricant...I use thread cutting lube. I use the same lube drilling a hole...bought a 4 oz bottle in 2009 and still have over half of it left. By the way the 6mm tap I have, I've must of used it over 100 times.
 
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umm... perhaps this is obvious - but carbon steel is brittle, thus all taps are "brittle" & in fact the cheaper the tap, the more likely it'll be a softer, lower grade steel & slightly more likely to bend before it snaps.

Trust me, I've broken my fair share of both cheapo ones & quality taps lol, it happens sometimes even with the best sets, good cutting fluid & technique (generally 1/4 to 1/2 turn out for every 1/2 to 1 turn in for aluminum) - nowadays I jus' borrow 'em from my buddy's 25pc Snap-On set... which cost $500 & breaks jus' the same - difference being free replacements ofc.

What the major problem really is (other'n dulling) with the cheap tap & die sets are irregularities, the threads they cut aren't nearly as clean & accurate as the quality ones, part of this is dulling but it's also due to the cutting edges being sloppy - they don't always line up with each other perfectly, making for oversized & sloppy threads - tap or die, same problems.

Still - I will say this, if it's a choice between a cheap set or no set at all... go ahead and get the cheapos as they are a pretty essential tool - but don't expect them to be great... & if you do spend the big bucks for the quality, don't expect them to be unbreakable - in fact, expect them to break & use accordingly ;)
 
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