Re: how much better is this?
I have a question regarding the 'shim' idea. If the builder takes the time and mounts the engine correctly, that being, making sure the inside diameter of the engine mounts fit the frame perfectly, something I stress by the way, how in heck are you going to 'shim' the rear of the engine and keep the front mount saddled against the down tube like we all suggest. Full contact between the engine and the frame is important but if you stick a shim/s between the rear mount you've effectively changed the angle that the engine would normally sit. That's what you do to shorten, adjust the chain tension, correct? Maybe you're relying on some misalignment in the front mount which will allow the engine to 'tilt' forward, but if that's the case then the front mount isn't setting how I feel it should for full contact throughout the inside surface.
The ideal method would be to have long drop-outs that allow for rear wheel position change, as do motorcycles or any industrial chain drive application. Unfortunately most bicycles do not have these and unless you're a fabricator capable of building this feature into a frame you're stuck with the dilemma of keeping two chains adjusted correctly. In the case of single speed bikes with no rear derailer or vertical drop-outs, this is where some means of tightening the engine drive chain becomes necessary.
I agree wholeheartedly that the kit supplied tensioner bracket/wheel is the weak link in the typical 2 stroke kits and coupled with the lack of mechanical skill we've all seen from numerous builders, it will remain the biggest stumbling block to a successful build, especially for the beginner or those with limited fabrication skills/equipment.
Going back to the dreaded 'drilling holes' discussion, Goatherder possibly missed my previous post when I said I will shun the idea of drilling holes to mount engines. That would be absolutely absurd, imo, and most others here.
Personally, I like the idea of having some means of adjusting the drive chain tension other than having to loosen engine mounts and 'shimming' them, or moving and realigning the rear wheel. That's one reason I like a chain tensioner but I have not used the kit supplied brackets or wheels on the last five bikes I've built. There are photos of the welded design I've incorporated into the my bikes and on one I actually used a part of the kit bracket and welded it to the chain stay. Tension adjustment then becomes a simple task of loosening one nut and sliding the wheel upward to tighten the chain.
There is just no easy way around this for some builders. They either have to utilize the kit bracket and hope for the best or take the advice given here by experienced builders who have lived through the initial bug-a-boo of keeping the chain tight and have found alternatives to the kit method.
This (tensioner) discussion will never go away and as long as we as builders/mechanics come up with ways to do things, there'll be differences of opinion on which way is best. This is where newbies need to devote the time to rear, read, read and make their decisions based on all the advice given here.
Like the man said. "Nobody's right, if everybody's wrong".
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"