Handlebar clamps not working well

[dirtrider998]

just assembled a mega moto 212 tillitson from GPS. I tightened the 2 U-clamps that squeeze the handle bar really well using an allen key and tapping it with a hammer instead of twisting with the hand, seems I got them as tight as possible but the handlebars slips a little forward/back, like when I pick the front end up to turn the bike around the handlebars pivot forward. They manufactured ribs on the handlebars where it clamps but it's not helping.
IDK , I see people wheeling this bike on youtube thus pulling on the handles and the last thing I want is my handlebar to slip forward/backwards. I ride bumpy woods trails that can be a lot of pressure on the handlebars.

I Was thinking to drill and tap threads and install a 1/4-20 grade8 bolt in each clamp and use permanent threadlocker. The handlebar metal is about 1/8" thick wish it were thicker but I don't think like the pressure I'll put on it will be nearly enough to shred the metal, it's about 1" tubular metal. The U-clamps are decent thickness to get some good threading into, about 2.5" total bolt threads.
Then I'll probably hide this with a foam handlebar cover for safety but I worry about these things like I'd like to just keep an eye on the bolts to make sure they're good without having to take the foam guard on and off.

Any other suggestions for this? I have 1/8" rubber sheet I could try and sandwich in there instead of drilling but maybe that'll slip too. I feel drilling and threading would be the strongest option but could weaken the handlebars a tad but again, it's about 1/8" thick 1" tube steel, so it should be fine.

 

[dirtrider998]

I'm referring to these
7/8" Handlebar Riser Clamp Kit

BTW, only one half is threaded which it doesn't show the threads in the photos, or neither is threaded and the threading is on the dashboard where these bolt in, mine have recessed hex head allen key fasteners I'd rather the regular hex head bolts in the link seems I can get them tighter with a breaker bar and socket rather than banging on the L-shaped allen key with a hammer. Got to bring my bolts to the store thread checker and replace them with grade-8 hex bolts, grade 5 would be fine but only a bit more $ for grade 8s are stronger and more corrosive resistant.
So, someone suggested just grind down the flat section of these. Good thing I asked before drilling because that should work good, someone said drilling a hole in round metal will weaken it. I'll also sandwich some thin rubber in there was agreed to benefit.

 

[dirtbkr188]

FWIW, 1" handlebars don't fit in 7/8" clamps

 

[dirtrider998]

I'm replacing the clamps with a much better motorcycle/dirt bike kind which is said to be the most secure, costs like $180 or something but I don't care. If I can retro fit these even if have to drill new holes will be fine, the frame is strong there.
It's common even for motorcycles the bars slip.
The clamps themselves on this mega moto are such light cheap metal I don't trust them even if I can get them super tight, it's that cheap metal the looks like cement when it's cracked.

Some put a strip of soda can as a shim but I'd rather use sandpaper I think the rocks will give a good bite, then evne with the upgraded clamp I might have the car shop here weld the outside at the engle I prefer it.

there's also aluminum mesh strips meant for wood where a screw strips the wood and doesn't grab anymore but once tight the soft aluminum will basically be flat like a soda can. Some use red permanent locktite thread locker but I don't trust that at all, not hard to break that seal.

When riding standing on bumpy trails, last thing I want is the handlebars to slip, so I'm not skimping on this.

 

[dirtbkr188]

Post some pics of the clamps you have on your bike, there may be some pitbike clamps that will work for you at half the cost.