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XR100 - XR75 flattracker - Year of motor?

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Hey all... I bought a xr100 motor in an xr75 frame, set up as a flattracker... Yeah, I know... What the hell was I thinking? Lots of cool parts though: mini-knock-off rear wheel, Afam bars, Jemco pipe. Bought it as a non-runner, no compression. Took off the rocker cover and found the exhaust valve collar busted in two. Half the collar and one of the keepers laying in the top... the rest must be down below. Time to tear the top end down and try to clean out the bottom end, but I don't know what year this motor is.

The motor number is HE03E-5200776... tried searching the web and got results from the early 80's to late 90's on the HE03E prefix. Does anyone know how to tell definitively what year this motor is so I can buy the right parts the first time?

Thanks for any help, I appreciate it! Looks to be a cool project, I'll post up pics for fun as I clean it up and get it sorted out. Feels like a death trap at the moment with seat height/wheel base/rider position!

Thx,

Kyle#44x

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bump... Even a link to a site that I could ID the motor year would be great! Ready to get this bike running, but I want to be sure of what year! Thx for any help!

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Thanks man!! Good thing I waited for a reply, would have bought valve train parts for an early 90's motor. Heck, maybe they are the same? I have a lot to learn about these motors now. Clutch feels very manly on it... also could have a big bore! The guy who built it was known to build 120's.

Thx again... Kyle#44x

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would love to see a pic of your bike. I am building a late 90's xr100 with an xr75 look to be used for flat track.

wayne

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cmsnl.com has your (pretty well every) parts fiche. Pricing is in Euros, whatever. Don't buy there, buy at your local Honda dealer or here on TT with the part #s you locate at cmsnl.com

Stiff clutch lever is a common complaint for the 'hundred. Flattracker does seem to be a common build this winter. Lots and lots of available bolt on parts upgrades and machine work available for the 100, 79-84 will provide the most direct swap parts. There are some changes in the bottom end 81 and up.

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79-84? Thanks for the info... Thanks for the link for parts identification too! Glad to hear that lots of people are building flattrackers... its the most fun I've ever had on two wheels! I did pretty well on my Baker framed xr250 fire breathing monster this year. Overall 2nd place locally in the Vintage 400 class.

Here's a couple pics of the little xr I bought:

xrhotrod003.jpg

xrhotrod001.jpg

And the xr monster w/newly adopted Austrian friend:

ktm1.jpg

Thanks again for the help!

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Hey Kyle

Bob Munday here we have run a few races at the same place if you remember. We had xr100 flattracker #3 ran at jeeps in the spring. Nice find

like the look. You need to see if you have pointless ignition, it takes 50% of the hassle out of these motors. Also this is a good place to remove lost parts.

There is a very knowledgeable guy here goes by gman might search for his posts on these little motors. Wish we still had ours after the spring race at 81 and jeeps someone stole mine out of the garage. Moved my xr200 and my crf450x out of the way to get my 100, it was a sad day. Thats all they took so I think some kids still hopeful but its fading fast. That is a great class at GPFTS. I'd pull the top end off see what I had, hopefuly high comp 120cc and mega cycle 129x cam. If I can help I lurk here and gpfts see ya

Bob Munday

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Hey Bob... Good to hear from you. Sorry about your stolen bike, that little sucker was FAST! Fast enough for them to come down on you for the flatslide carb... if I remember right.

Thanks for the tips... I'm trying to hold off tearing into it too deep until after xmas. I got a couple of days off coming up though, might have to poke around and see what I have inside this little thing. Not sure how far to go with it... the wheelbase is just too small for me, and too small for Charlie too. We really picked it up for him to ride in the 150 class just for fun. If we are going to get serious we would need a much longer swingarm or an xr100 frame for it. Cool little bike though!

Take care and hope to see you guys at the track!

Kyle

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Hi kyle

There is a 100 twin shock frame on okc craigslist for a deal. As you remember I'm a fairly big ole boy myself. What I did was move the handlebars forward 2 inches and up 1 inch I used old set back bracketts but reversed them this really opens the cockpit up. look on the edge of cam lobes for any #s, look thru plug hole to see if you have piston dome. Have a great christmas and we'll see ya at sping race. BTW Jeremy is having great races in Stillwater at Lazy J you ought to come down info on ftm.

Cya Bob

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Hey Bob, Thanks for the setup tips... I've been asking around about a 100 frame. I think the engine will fit frames from many years. Just not sure how deep I want to get on this project. If I change the frame, that means all new footpeg mounts, exhaust, etc, etc... Might be better to get it running, clean it up a bit, and get my money back out plus. Might be better to put the money into a 150f or newer 100 w/kit.

See you at the races,

Kyle

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I don't know what you have in it, but I'd prob be a player if you decide to step away from it. Not alot of fun to watch my boy race and not get a little track time myself! I have been looking for a vintage bike like a tt 500 or a 350 honda but another maddog bike would be a start.

Bob

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Hey Bob, Not too much in it... and I would pass the good deal on to you if I decide to sell it. Now that we are past the xmas holiday (and the weather is nice) I'll pulll the head and see if there is any damage to the piston, valve, or head.

Keep looking for a 350/500... I'm hoping to have a 350 ready for next season too.

Kyle

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Turned out to be a bent exhaust valve... so no compression. Valve retainer broken too. Luckily both halves of the retainer and both keepers stayed up in the top of the motor... I just couldn't see then in there.

When I cleaned up the top of the piston it became evident that it was "custom ground" to fit the combustion chamber. Has a domed top and sort of relief pockets for the valves ground into it a bit. Measures 58mm... I think makes it 118+ cc's. Not sure if the marks on the ex side of the piston are from the valve hitting the piston and then making the keepers let loose? Previously when I have seen a bent valve or stuck valve the keepers are still in place in the retainer. Or did the keepers let the valve fall into the chamber and THEN get bent? Any advice?

Also appears to have a Megacycle 129-00 cam in it. Had the number 12900 on one lobe and 3*98 on the other (asterisk should be a degree mark), so upon searching the net I found references to a megacycle cam of that number.

Interesting little motor that need repaired and some tlc... but I don't know how deep I want to get into building another flattracker from the frame up. Projects like this can turn into a money pit real quick!!

If I can find an xr100 frame real cheap it might be do-able!

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Well, I finally got my parts and replaced the ex valve, retainer, and keepers. First thing I noticed is the stock retainer is different that the super-lightweight one that broke. Titanium or aluminum I guess... but everything went together just fine. So I put some putty on the ex side of the piston to check clearance and the best I can tell it is about .012"... pretty tight. The bad news is that when I snugged the head bolts down the exhaust clutch side bolt started pulling up out of the crankcase with about 2 lbs on it... dang! Then I remembered that one was loose when I took everything apart. So helicoil time I guess...

xr100head.jpg

A couple of question if you guys don't mind -

Any clue what kind of lightweight retainer is on the intake side?

What are the torque specs for the xr100 head bolts (4 main ones and one smaller side bolt)?

I need to gain some clearance for piston/valve. Will newer head and cylinder base gaskets fit the '83 motor ok?

Any tips on getting a yamabonded cylinder off the crankcase (without breaking any fins... lol), that sucker is STUCK TIGHT!

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If that intake retainer is black, then it's probably aluminum, because a Ti retainer would be natural. No idea who made it.

Use a rubber mallet the free the cylinder from the cases.

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If that intake retainer is black, then it's probably aluminum, because a Ti retainer would be natural. No idea who made it.

Use a rubber mallet the free the cylinder from the cases.

Thx for the advice... It is indeed painted black, and the light silver ring you see around it is the paint being chipped off by the rocker arm... which is touching the edge of the retainer with the valves adjusted so loose. The weird thing is that the motor was exactly like this when I pulled it apart, so someone bent a valve, lost compression, thought the valves may have been adjusted too tight, loosened them substantially, and kicked the bike over until it broke the ex side retainer? I'm still trying to read the tale this motor is telling me... so far its a horror story! lol...

Any idea of torque values for the head bolts? I borrowed a helicoil kit and hope to fix it up tonight.

Thanks again!

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