Megacycle Cam'd Bbr 120!!

[gman255]

As a budget BBK the BBR120 is a great kit, and the most complete kit on the market! Well.... After dig'n my teeth in to the kit and discovering the mild camshaft.

It was time for a little performance upgrade. I opted for the Megacycle 129x6 cam to wake up my BBR120 kit!

Crunching the cams numbers

Intake~~~Exhaust

.300~~~~.281 lift

256*~~~~256* duration

102*~~~~105* lobe center line

Also deck the stock 100 cylinder head .025 this yields about 1cc smaller combustion chamber. Stock BBR 120 CR 10.5:1 this will bring my compression up to about 11.3:1! I will be run'n a 50/50 mix of VP, or some 103.

There may be a 12.1 piston in my future?? This would give me about 13.3:1 CR with this head:busted:

This camshaft application was far from a bolt in. However, I did not have to clearance the rock box as much as I expected for lope clearance. Or the for rocker arm interference thats the good news.

I my initial cylinder head mock up was far from a success. I crudely assemble the head with out adjusting the valve lash to spec, for a rotating bench test by hand. I had about a 1/4 of a turn before a restriction in movement. The result was From Major valve collision. Adjust lash to spec intake at .004 and exhaust .006" there was only .012" clearance between the valves at overlap. No room for oversize valve from what is see with this cam?

My second interference was valve guide to retainer on the exhaust. My head is a 1995. So... No seal on the intake valve. I used a razor blade to slice off a hair or two off the guide and had to remove about .010-.015 from the back side of the retainer.

Engine mock up was just short of ugly! Most likely do two my .025 off the head (isn't helping) after claying the piston I had about .015 clearance on the exhaust side (which is bad news should be about .080 according to Megacycle) and about .025 on the intake.

Knowing the decked head is slightly retarding the camshaft timing, I slotted the upper cam gear and degree the cam straight up I was off by about 3*. This didn't help my valve to piston issues. The only option was to clearance the piston. I removed about .040 from the exhaust and .020 for the pistons valve reliefs. All the material was taken from the angle of the pockets. This was a long process repeating the claying the piston and degreeing the cam before reaching acceptable piston to valve clearances.

I replace the BBR spring with KimbleWhites recommend by Megacycle and also replace the BBR rocker with the stockers.

Yes I'm missing some key pictures... Sorry guys

It's sound pretty MEAN! I haven't got it out of the basement for a ride report yet. Mototown's Master of Minis In a 12 days and counting!

[gman255]

Masters of Mini's Mototown event was absolutely a freaking blast again!! To bad it will be the last:foul:

Let me tell you, The Megacycle cam and deck head was an AMAZING IMPROVEMENT over the stock BBR 120 kit!! This motor PULLS HARD through out the rpm rang! Right off idle, wicked mid, with plenty over rev. By no mean did this compromise the the BBR's low end power, in enhanced it at every crack of the throttle.?

Completely and totally satisfied with my MegaBBR kit:smirk:

Another point or so of compression, it would be the snizzzles!

[4strokeridertt]

The Engines Only stage two 120BBK comes with a Megacycles cam and the piston is clearanced already. plus the kit comes with springs, clutch, and more.

http://www.xr100.com/crfxr100.htm#CRF/XR100 120cc Ultimate Big Bore Kit

[cam120]

Thanks for posting.... looks interesting:thinking:

[gman255]

"The Engines Only stage two 120BBK comes with a Megacycles cam and the piston is clearanced already. plus the kit comes with springs, clutch, and more.

http://www.xr100.com/crfxr100.htm#CRF/XR100 120cc Ultimate Big Bore Kit"

I never lived under a rock! I sure can make use of one!

This thread was for intended for educational and inspirational purposes that there is a performance alternatives for an existing BBKs. Isn't that, what these forums are about:thumbsup:

[cam120]

I was impressed with the bbr120 kit over the stock... how much does this cam cost again?

[gman255]

You'll be just as impressed...

With a core, the cam was about $120 and $40 for the KW springs.

http://www.megacyclecams.com/

Web also has a great selection of grinds

http://www.webcamshafts.com/

[rdl428]

I just took a Powroll Cam and put it in my BBR120 Kit the other week. No mods required and it runs really good. Super strong low end torque right off idle and into the mid-range.....a lot stronger than the BBR. It signs off a little earlier up top when compared to the BBR cam but I wanted that low-end style of power.

I should have took some pics to show you guys the difference between the two cams. The Powroll definitely has more aggressive (steeper and taller) lobes. I didn't do any measuring or anything. I'm the type of guy who just drops it in then test it with "butt dyno"! Just an FYI that may help.

[lazylarry]

I just ordered a BBR 120 kit. Will it change my jetting ? Any other suggestions as far as assembly or whatever would be greatly appreciated. This is my first experience with a 4 stroke but I do have a manual. Im a little concerned with getting the cam timing off one tooth. I heard you need to make sure the front (of the bike) side of the chain is tight at assembly. Thanks for all info.

[gman255]

Yup, it will change your jetting. The Kit includes a recommendation for a 105 mj on the stock 22mm carb. Depending on your other mods you might be able to play with 105-110ish for mj.

Almost every one on this forum will recommend a 24mm 200x carb. Plenty of information on this forum about the carb and jetting. Use the search opition.

This engine is nothing to be worried about. If you can do a 2t you can do a xr100. For newbe 4t advise: Be sure cam lobes are pointing down and valves are closed. Loosely put a zip-tie around the timning chain (easer to fish it out of the cases when it falls in lol) Check ring gap and piston to cylinder wall tolerances before final Assembly. I peffer to place one c clip piston and place the piston in the cylinder, than mount it on the rod. Use plenty of Assembly lube.

Be sure the timing chain is on the lower sprocket before attempting to put it on the upper gear. Mount the timing chain on the upper sprocket before installing the gear on the cam, lossly start the cam bolts. Leave the cylinder head timing chain guide adjuster out until your ready to check the timing mark alinement. Its easer to jump timing teeth on the lower sprocket. If your off a tooth or two. And yes, the chain must have all the slack out of it. The guide will take care of it after installing the cylinder timing adjuster, to verify the timing marks are aliened.

Hopy this helps

Good luck with your first 4t:thumbsup:

[lazylarry]

THANKS FOR THE INFO, BIG HELP. wHEN YOu talk about checking ring gap, is there a chance there could be a problem. I mean if Im buying the kit shouldnt everything be already checked. I thought you just put the rings on the piston, squeezed them togetjher and put the cylinder on.

[gman255]

Your Welcome!

Most likely, there won't be any issues with the ring gap or piston to wall clearances. For my self, this out of habit, and for apiece of mind... It, only takes a minute to check the clearances.

Over the years I found what is easer for me... I always install the prepped piston with the rings, and one C-clip, in the cylinder on the bench. Then install the piston and cylinder on the rod. But, to each their own. Whatever works for you.?

[lazylarry]

thanks for the help. this project basically started out as getting a free xr 100 'running' that had been used and abused, but after i got it started i realized why it was free.......she smoked very bad so i figured by the shape of the piston cam and cylinder that the bbr kit was actually the cheapest way out. the bike probably should have been parted out but now im in this deep, im going to make it nice, im just a little nervous because i didnt intend to get quite so much money into it. i didnt realize the carb was a 22 mm. im going to se this onejust for money reasons right now...starting to feel this economy crunch a little here. im hoping the cam chain is o.k. how do i check ring end gap. there isnt any real science to installing rings is there ?

[gman255]

Engine Assembly, and acceptable tolerances are all stated in the service manual. The BBR kit assembles the same as a stock replacement.

Please feel free to PM me, If you have any other Q's.

There is a XR 100 Top End Rebuild thread started on this page (if you haven't see it) that may give you some more in site.

All the best

[Cslong324]

Hey! Yall seem to know a lot about your 100 BBK this is what I've just completed. A 2006 crf100 with the 120 wiseco 12:1cr. And a hot cams cam shaft. Big gun rev box and stock carb. What jetting fuel screw settings do you recommend? I also have a 200x 26 mikuni as well. What recommendations on that? Which setup do you think I should use? I just want to try to give my brothers bike for the race season to be as peppy as it can be.

[socalxr]

That post is 6 years old.