michaelmoore Posted March 11, 2008 Report Share Posted March 11, 2008 (edited) My KT250 needs to have the under-engine frame rails pounded back away from touching the engine. Again. I'm very tempted to just cut them out and go with an aluminum plate shield instead. What's the usual thickness and material used for this application? 3/16"/4-5mm and 6061-T6? Is there a bit of air space left between the plate and engine or do you run a sheet of conveyor belting or something similar in there to add some additional cushion? cheers, Michael Edited March 11, 2008 by MichaelMoore Quote Link to comment Share on other sites More sharing options...
swooshdave Posted March 11, 2008 Report Share Posted March 11, 2008 Any chance you could fit a bash plate from an existing bike that uses it for frame structure? I think later Bultacos, OSSAs and Yamahas (of the top of my head, meaning I may not have got all three right) were so fitted. Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted March 11, 2008 Author Report Share Posted March 11, 2008 It appears that by the early 1980s many if not most of the bikes had gotten rid of the under-engine frame rails. I suspect that even if I started with some other bike's plate I'd have to chop/bend/weld on it before it fit right. Sometimes it is easier to make what you want right from the start instead of modifying something else. Unless of course you get very lucky. I might end up needing to borrow a friend's press to do the bending if the plate is quite thick and hardened, but I can do any machining/welding here at home. I can get a piece of plate delivered to my door the next day if I place an order by 4PM. 1/4" seems like it might be a bit more than needed. But maybe there's a trade off between "a bit more than needed" and "take off once a year and flatten it back out." The existing frame rails seem to have gotten into the stage of being a routine maintenance item. cheers, Michael Quote Link to comment Share on other sites More sharing options...
feetupfun Posted March 11, 2008 Report Share Posted March 11, 2008 Michael 5mm structural aluminium would be OK if you include lots of stiffening either creases of ribs but they usually end up looking terrible. I reckon 6mm structural is the go. The rubber insert helps a lot with avoiding the plate being bent and also quietens the plate down nicely. Even 6mm structural will eventually bend with use without an insert. Quote Link to comment Share on other sites More sharing options...
mcman56 Posted March 11, 2008 Report Share Posted March 11, 2008 I made a Reflex skid plate out of 3/16 5052 and it seems to have held up well. It uses the original hard rubber spacer from Honda. My Sherco is more like .156" but has some stamped in features for strength. I'm in the process of making a press brake to try and form the right radius for the Sherco so I can make a thicker one. Ads for general off road bike skid plates vary from 5/32" to 1/4" and 5052 to 6061. Quote Link to comment Share on other sites More sharing options...
swooshdave Posted March 11, 2008 Report Share Posted March 11, 2008 I made a Reflex skid plate out of 3/16 5052 and it seems to have held up well. It uses the original hard rubber spacer from Honda. My Sherco is more like .156" but has some stamped in features for strength. I'm in the process of making a press brake to try and form the right radius for the Sherco so I can make a thicker one. Ads for general off road bike skid plates vary from 5/32" to 1/4" and 5052 to 6061. I assume the Reflex did not originally have lower frame rails? I believe he Michael is talking about removing the lower frame rails and replacing them with the bash plate. I would think the rigidity factor would need to go up. If you're not going to use an existing bash plate, I would think the dimension of one would be a good starting point. btw, there was a M49 on ebay a while ago that appears to have been modified the same way. Quite interesting. Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted March 11, 2008 Author Report Share Posted March 11, 2008 (edited) Don Morely has a photo of an early Sherpa T at the SSDT where the owner (Alan Morewood) substituted an alloy plate for the bottom frame rails. He doesn't give a date but his text indicates that this was before Miller did something similar. From the paint job and exhaust it looks like it might be a Model 27. That looks like a nice job on the Reflex. I'm considering some wings like that to protect the side cases. A flat plate isn't going to be adding much to the structure. Then again, the way the existing frame tubes seem to creep upwards they aren't too wonderful either. I'm looking at the frame to see if I want to add in some extra bracing tubes anywhere. The main concern would be force on the front wheel trying to bend the frame at the nose of the seat. I'd prefer to not have the engine acting as the structure to prevent the bottom of the frame spreading apart though the KT does have some decent motor mount lugs so it probably wouldn't be a concern. I've got some photos of what I think is a Gollner KT250 that I'll have to look at as it uses just the skid plate and no tubes under the engine. I'll probably go with 1/4". There's no sense reducing on the thickness to save a few ounces if it means it needs to be reworked more frequently. cheers, Michael Edited March 11, 2008 by MichaelMoore Quote Link to comment Share on other sites More sharing options...
tlrider Posted March 22, 2008 Report Share Posted March 22, 2008 Keep in mind any welds on aluminum will be soft and therefore not structural for use as a stressed member. Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted March 22, 2008 Author Report Share Posted March 22, 2008 I'm definitely aware of that. I need to check with a friend who is in the machining/fabrication trade and find out who he has do heat treating. I think a lot of the welding can be done in a way that qualifies as substantial overkill so that HT isn't needed, but if a lot of welding/bending needs to take place it may be easiest to start with something in "O" condition and send it out for HT. cheers, Michael Quote Link to comment Share on other sites More sharing options...
tlrider Posted March 23, 2008 Report Share Posted March 23, 2008 Michael, I have held off doing an aluminum skid plate for my TL125 for that very reason. Take a look at the BPS engineering site http://www.bps-eng.com/ and look at how they did the bash plate on their TL Pro kit. They have added steel mounting points to the frame. That is how I am going to do mine, started on it today. Quote Link to comment Share on other sites More sharing options...
matty Posted March 23, 2008 Report Share Posted March 23, 2008 (edited) Iv'e use this in the past quite easy to use and i was very impressed used it for the hole in the side casing from the kickstarter http://www.easyweld.com/store.cfm/pid/25/ Though it might come it handy if welding up your bash plate http://i244.photobucket.com/albums/gg24/ma...ur/100_9612.jpg http://i244.photobucket.com/albums/gg24/ma...ur/100_9611.jpg Edited March 23, 2008 by matty Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.