OzVMX Forum
Clubroom => Tech Talk => Topic started by: 35elsinore on October 18, 2011, 03:18:37 pm
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Need some feed back on my new project. As a lover of everthing honda, a XR75 impressed me at the coffs harber national. After much thought of building a pre 75 fourstroke for 2012 nationals I have decided to fit a K1 XR75 engine into a 73 cr125 frame. I guess this has been done before but myself have never heard of anyone doing it. The thing I need help with is getting the most out of the 75 engine to compete with the bigger bore bikes. The XR75 at coffs harbour went very well so if anyone knows this gentleman and maybe a contact number it would be much appreciated. Would love to have any feed back eg: im wasting my time etc. or any info on suppliers for go fast bits.
Thanks Troy
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Did it have an Sl125 barrel.
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Here's some pics of one in progress on the VCM website.
http://vcmweb.ning.com/photo/albums/xr75-engine-progress
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Didn't FMF do it in the 70's with a bored & stroked engine out to 110cc ?
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I started to do my XR a few years ago and it got shelved, more important projects to do.
The go back then was to have a SL 125 sleeve put into the XR cylinder, have the engine cases machined to accept the bigger sleeve and you have to have the con rod machined to take a 14mm gudgeon pin and you fitted I think a Kawasaki GT550 piston (I still have all the parts to do it somewhere) you need to have the head O ringed as well. From memory a guy called Glenn Stayley in the Sevill area in Melbourne does them..
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What do you weigh mate, under 50kgs one hopes on a wee thing like that.
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ask steve gall his was very fast back in the day
jim
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Thanks for the feed back, just what I was hoping to get. EML, 79kg light haha. I love riding my 125s an know how much more fun they are to ride compared to my 250. This was my train of thought with this project. The corner speed you can keep compared to 70% of the field being heavy XL350s hopefully will compensate for the lack of power. Viper79 are you interested in selling any of your mothballed project. Cheers Troy
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G-day there Troy, yeah that was my XR75 at the Coffs Harbour Nats a few years back. It was a pity i smashed my knee up a little in the second race as i was planning on knocking a few noses out of joint by beating the big bikes. Oh well ! Yep the little things a rocketship that took a few lunched motors to get it absolutely bullet proof. Has had a bit of history in the VCMR a few years back taking out the 4 stroke All powers title for a few years running and yes it did upset a few blokes on their hotted up big bikes. Haven't raced it since Coffs but i have been known to disturb the peace at the HBBB on it. Gave it a nice new paint job for the 70's MINI BIKE reunion we had here in Victoria a couple of years ago. I'm not real sure how to post a photo of it on this thread but if you look on my page there is a couple. By the way it's also a methonol burner too. Regards Les Barfoot
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Thanks Les for the reply and memories. Any hints on the bulletproof stuff or are you interested in building another engine. Seems the more I dig the more surprised I get at how many hot XRs are out there. The idea of putting the engine in a 125 frame is for the bigger wheels and ground clearance to hopefully save my knees and kidneys.
Cheers Troy
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Have a look at these www.xrminiracer.com There is an XR section on www.vintagefactory.com ,If you wanted to use the stock frame an elsinore 125 front end will virtually go straight in using the original front wheel of course you would then need to jack the back up to suit,there is no easy or cheap way to hot up the 4 speed donks but as Les has proven it is possible , I think the 75 motor would be to small for the 125 frame & would go for a hotted up SL100 or 125 motor but i guess that's going away from your original idea :)
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There was a guy that raced one down to Baja one year-that would be a good story to find again. maybe in Dirt Bike or Motocross Action.
I just modded a kids exhaust on an XL185 and it at least sounds the goods now.
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Yeah Troy the motor runs a kawasaki 550 piston in a SL125 sleeve. Not much room to play with inside an XR barrel so the sleeve fitting must be precise. You will need to do a little head work to fit the piston diameter and not to mention a port job to feed the thirsty mongrel. As previous said a bit of rod work to fit the bigger pin too, a copper head gasket to hold in the compression. Cases must be machined out a tad and re routing of the oil feed. Some just run external lines but mine are interal but modified. A lumpy cam, trick valve springs a nice big carb and manifold that drinks methonol, a CDI ignition mines a 1974 elsinore 125, a barnett clutch and springs and my favourite a grouse reverse cone megaphone so the big bikes hear you coming. If it's all done properly you will have one sweet motor.
Myself i wouldn't put it into a 125 frame for big wheels. Just lift up your XR with 125 elsinore front forks a DG style swing arm with longer shocks a 17inch front wheel and re upolsted seat a couple of inches higher than stock and you end up with one very roomy XR75 that still looks like an XR 75 with all the leg room you need. I'm 180 tall and 78kgs and its perfect and so much fun to ride. Hope this is of some help.... Regards Les B
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What is the capacity of your motor Les? So it's not stroked then?
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No Smed it's not stroked. Didn't want to start mucking around with spacers etc. Wanted the external of the motor to look stock. To my belief it is around 116cc or there abouts. Regards Les
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Thanks again Les your help, its priceless. I guess the cr frame was an idea with the thought to be a bit different aswell. Thanks Smed for the links. I have had a quote off of XRminiracer for a engine $3200 But have to send my engine to the states as they cant supply. Was hoping for a bit cheaper option thats why I posted this topic. The engine I have already prelimenary fit to a frame, it does look a little small next to my 125 but certainly not totally out of place. The rear bottom mount is original with a spacer each side. The front mount I have made out of aluminium and amazingly diameters of engine and frame mounts are the same width. The only hassle I can see maybe the inlet manifold/carby as the cr frame is dual pipe for the side port head. It does seem a shame to see my K1 XR75 sitting there without a heart tho.
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I do like your idae elsinore but check the weight diffs 1st. The Cr frame might work better as you will have room to mess about with weight distribution back and forth as well as up and down for the best balance.
The larger CR wheels will work better if it gets rough as well. And it's not been done before that we know of.
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I did this years ago when my boys were growing out of their XR75. Found an early CR125 frame and a Thor aluminum swingarm to fit it. Added a Clarke mini tank and MR50 custom seat with some old Curnutt shocks in the back. They had fun on it running in the desert. Had to cut and bend the right side frame tube for the carb to run back. Found out that the early CR frame had some double wall tubes in it! That surprised me. I will try to find a pic of it.
Swiss
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Thanks Swiss a picture would be great. I guess you rode it aswell, can you remember how you mounted the engine, what position and did it turn like a cr125. Cheers Troy
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Sorry guys, this is the only pic that I have of it other than a distance shot of one of my older boys riding it in the desert. This was when I was taking it apart to rebuild the stock XR75 frame for my youngest to learn to ride on. I had just thrown it together with the CR125 frame and the XR75 engine for the older boys to have something to ride. I had already pulled the pipe off of it. Mounting was simple since there was lots of room. Lined up the chain, set the front sprocket at about the same height as the swingarm pivot and cut up some mounts to fit. Used a sock filter since it was mostly ridden in the desert and we weren't worried about mud etc... The kids loved playing with it.
(http://i346.photobucket.com/albums/p438/sscf_2008/XR75CR125chassis.jpg)
This son is now 24 and in the Air Force. Time flies when you are having fun!
Swiss
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I was reading an article a couple of days ago (Popular Cycling from sometime in 1976) about an XR75, bored and stroked out to 116cc..
I'll dig it out tonight and scan it if you want.
The Dyno charts before and after were quite interesting.... 2 to 2 1/2 times the horsepower EVERYWHERE, and the same increase in torque..
Trying to remember what they did.
bored and stroked to 116cc
10.5:1 compression head
new cam
larger head studs to avoid blown head gaskets
bigger carburetor
internal rotor ignition off something else?
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Thanks Swiss what a corker. Spose ya wont have to raise the foot pegs for him at 24 then.
Any info IT400C would be appreciated. Was that article on the net or a mag. 2 to 2.5 times more horse power I might have to de-tune it. :D What a huge improvement, just what Im looking for. Thanks
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I built up one of the XR116 engines and the one in my son's XR75 pictured above was one of them. Guy contacted me about building the engine up, said that he had found the "Powroll Kit" on EBay and wanted to know if I could put it together for him. It had everything but the cylinder sleeve and I did some research and found that I could use an old 175cc twin cylinder sleeve for the kit. Worked out real well. I have the kit info and the article all scanned if someone needs them.
Swiss
[email protected]
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Yeah, it was the Powroll Kit in the article I have. (from a magazine at home)
Swiss, is your article from the (I think) June 1976 Popular Cycling?
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Yes I think it is a '76 issue, I took all of the articles that I thought were of some importance to me (mainly Thumper articles) and pulled them out of the magazines and put them into folders. Otherwise I would have a room full of old mag issues. I was getting 7-10 mags per month between bikes and cars for years and had stacks of mags 6' tall along a wall. Had to trim them down. Didn't know that years later I could have sold some of them on EBay for more than I paid for them! HA!HA!
I also have the Powroll build sheets for the engine, and the old Powroll catalog pag where they showed the 116cc dyno run compared to stock. They showed 10.3hp vs. stock 4.5hp on the Powroll dyno sheet.
Swiss
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Swiss would it be possible to email the scans of the mag. Wonder if anyone would have a kit laying around. Cant thank you enough.
Regards Troy
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Troy, I have emailed you three pics of the Powroll article
Rob.
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Why don't you contact Powroll and see if they have the parts you're looking for... they're still in business.
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They are in business, still but in big trouble apparantly and really struggling with workload that is affecting their customer service big time. They are currently not operating to their usuall high standards which have dropped considerably. There are several threads on them on some USA sites. Thumper talk is one i think and it is best you read those. I would avoid placing an online order with them and You are unlikely to hear from them. From what i have read, they have a huge amount of back log of work and they are kinda over whelmed by it all and its just 2 guys and the girl in the office trying get through it all. i think the GFC has had a big affect on them by the sounds of it and everyone is hoping they can pull through it as they are te only experts ding this sort of stuff at a high quality with years of experience. I wanted to place an order for a XL250 stroker crank with them but are going to hold off for 6 months a year? till their communication and customer service picks up because currently a huge amount of emails are going unanswered (worldwide), and you cant even get through to them by phone. The only way i have known people to get incontact with them in recent times is via a secret phone number direct into the workshop, that the public is not supposed to know.
Just one the XR75's, there is a XR75 specialist in USA that has NOS Lockhart Oil coolers for XR75's.
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Thanks everyone for your time and help. Starting to get a few options now.