Hi again all,

sorry for all the posts…. My build I am trying to make is a period type build rather than the road biased build I inherited. So I realise parts are not all 1970 RT1 but it looks so much better as a trail bike style and parts are coming from all over in all sorts of condition and colours. I am going to assemble a bike. Then tear it down when pretty much completed and paint and fasten correctly. Parts now sourced include a 71 seat. Correct front guard/fender (I think) correct top chain guard.  Air filter, tool case. Rear guard/fender from a DT2/3 I think. Clocks and bars. I also picked up the tank that is fitted in this picture. Not RT I think but looks right for my purposes whilst needing work. But the underneath is a narrower fit.  Does anyone have ideas what it is off please. It was advertised as an RT1/DT1 but I don’t think it is.  It has a similar stripe and badge locators. 

open to ideas please.  

share.icloud.com/photos/0cbRWNW8bUNf4gnfX4PCxPFTg

Just how i like them. Tank looks DT1 which is also RT1 so can't think why its narrower unless someone forced it narrower to tighten up on the front tank mounts. Hope you have an original decomp for the front of the cylinder although i'm not using one in mine. Good to see yours has the ignition advancer--retard for starting--in your flywheel. Keep that flywheel nut good & tight or it'll eat the crank key for supper.
photos.app.goo.gl/NTzfFLaLh5Xyrd1b7

Thanks RT.

Well of course I suppose it depends what tank was on it when I got it… it’s definitely wider than this one (let’s call it an RT1) as you can hopefully see in the pictures. But the unknown orange tank is shorter than an RT2 and DT3…. As well as wider for the top tube. The frame top tube rubber will not go near the RT1 tank so will have to get some rubber sheet or some such to mount it on. As I say, it looks right so it’s staying. Orange one who knows?

I don’t have the front decompressor my barrel/jug doesn’t have one. Someone has fitted an aftermarket one in the second spark plug hole in the cylinder head. I need to do a compression test on the RT1 as there is scoring on the barrel, though I have read on here they are pretty bombproof. If I have to reborn I may look for a different barrel/jug with the decompressor in. It looks neater than the aftermarket one.

I have taken the message regarding the flywheel.. it has been mentioned to me a few times. Breaker bar extension required…

Thanks again and see what you make of the pictures.

share.icloud.com/photos/089PD0G7_DJ7kaB-jSz3HLgoQ

The only 1970 design tank in your photos is the yellow one.  The others are all from later bikes and often can "fit" but are not an exact fit for the 1970-71 RT "badge" tank and seat combo.  

Check the 1970 parts list.  Pretty sure you'll find the 1970 tank has a rubber block under the rear as well as a sheet of squishy foam folded over the frame rail that supports the tunnel of the tank.  

Aftermarket compression release is not a replacement for the Yamaha "start assist" release that did not come on the first RT cylinders.

The modern "chain saw" knob-type release installed into the plug hole with an adapter works great for starting.  

Thanks MarkT,

Good news is I have the right tank even if it needs plenty of work. I only showed the silver and green tanks for size comparison of the orange tank the RT came with. The orange tank is shorter and narrower than the others as well as having a wider tunnel to the yellow one.

The barrel is original and I note the start assist came later. The head fitted after market decompressor just looks a bit clumsy? I am sure will work well and stop broken or bruised legs ankles and ego’s! When I eventually try to start it..

Thanks for all the info MarkT it helps be to build a picture of what I have. I now need to find a rubber damper block as you say as well as a tank fitting band and a foam type seal according to the parts list on cmsnl. One step forward!

Thanks again

"I am sure will work well and stop broken or bruised legs ankles and ego’s! When I eventually try to start it.."

Actually, it won't work very easily for starting, if at all.  Though with a lot of practice you might be able use it during starts? 

The cable operated spark plug hole compression releases were used as an "engine brake" similar to the Jacob's Brake used on diesels.   They don't provide a lot of braking, often make an oily mess, and some designs can suck dirt into the engine.  The cable-operated spark plug hole compression release was a fad of the late 60's and early 70's that didn't last long.  

youtube.com/shorts/VU1CMKRrfuo?si=4NzKP7OZoB20rC0T