Incredible Pit Bike Engine Build || CRF70 / CRF50 / XR70 / XR50 / CT70 / Z50

[@818Rico]

You’re the Man Brian 💪. The world needs you 🦸🏼‍♂️

[@brian.d.mobley]

Very kind of you Rico! Thanks.

[@AviatorAriana]

You did good job Brian 👌🏻 You explain well and you cover all details which is unique.

[@brian.d.mobley]

Thanks! You are always so kind with your comments.

[@be007]

i like your special torc wrenches 🙂

[@Xatos1337]

Wow. My chain came off and broke the exact parts that you mentioned on the stator plate!. Did not expect that at all. You saved the day for me! Thank you!!! Great video and thanks for the time stamps!

[@brian.d.mobley]

Thanks Xatos! Always nice to know one of your videos helped someone! Thanks for watching and for the good vibes!

[@silkcustoms520]

I live 10 minutes from TBolt. Vince and Jr are friggn Awesome

[@brian.d.mobley]

Hey Silk Customs! I could not agree more! They are fantastic. Smart, friendly, hard working and incredibly helpful. They’ve become good friends!

[@redlitemeatandpizza]

Great video, just got my engine apart, this is probably one of the most detailed videos out there 👍 hard to find these kind of videos

[@brian.d.mobley]

Thanks Redlite! I tried hard to keep it straight to the point and in order. I don’t think I missed anything because I went over it with a few other expert friends before I published it. Hope it helps! Thanks for watching.

[@redlitemeatandpizza]

When mating the crank case halves did you run into them being stubborn going back together?

[@brian.d.mobley]

@@redlitemeatandpizza Hey! I haven’t. And usually when you experience that, it’s because something isn’t installed or aligned quite right. Check you transmission shafts carefully to make sure they are fully seated and lining up with the corresponding machined holes in the opposite case half. Usually it’s something very simple. Don’t force anything back together or you’ll be shedding some tears! Take your time and check all your installations. You’ll find it!

[@redlitemeatandpizza]

@@brian.d.mobley Thanks for the reply, so the new kick start shaft diameter was a tad bit thicker than the old one, which was causing the Ring washer not to fall down to the snap ring, which caused the cases to not fully go down. Good thing for a dremel! Opened it slightly more and it fell down 👍

[@brian.d.mobley]

@@redlitemeatandpizza Thats great!! You figured it out on your own! Feels good to figure things like that out, right!?

[@cletussurfsalot7190]

At 20:40 the copper washer is on the bottom LT, then at 22:28 its on the bottom RT. Either way very useful video. THX..

[@brian.d.mobley]

As I recall, I put the washer in the wrong place at one point and had to re-film the clip with it in the correct position. Re-filming everything for a corrected mistake is not easy or time efficient, but I think you'll find the washer in the correct position finally. Thank you.

[@memedeck6026]

Love your videos they are very detailed

[@brian.d.mobley]

@@memedeck6026 So nice of you! Glad you find them useful!

[@forreststrong797]

You don't need to tighten the oil pump drive gear, it turns in the direction that tightens it. I always just snug it slightly. One thing I've noticed when rebuilding these engines is the timing chain tensioner tends to be worn out half the time, there's specs in the service manual to measure the rod. It works very similar to a hydraulic lifter in a car, if the rod is worn it won't pump up as well. Awesome video very thorough!

[@brian.d.mobley]

Thank Forrest. Good insights! Thanks for sharing. The manual was no help regarding that oil pump drive gear so I tried to just tighten it up to about the same resistance that it gave me when removing it. And for some insurance, I added the LocTite. Thanks for the insight on the tensioner rod too!

[@davelowets]

If there's dirt in the rod assembly, it wont pump up correctly either. If you press your finger on the rod with the cover off, and oil squirts out of the relief valve, you have a dirt issue. Remove and clean the assembly, and change your oil.

[@owenlachat1620]

Great Video. Keep the XR bike videos coming!

[@brian.d.mobley]

Thank you. I’ve gotten side tracked a little bit lately working on my Private Pilots License. I had no idea how all encompassing it would be! Thanks for watching.

[@eg4757]

Excellent video! Super helpful, no bullshit info in the way. Awesome job!

[@brian.d.mobley]

Thanks EG! Glad you liked it!

[@SpeakerKevin]

Wow, someone finally addressed the cylinder head arrow, that it needs to point downward. Also, place the gasket on the head cover to make sure the holes line up correctly as there's only a one in 4 chance you will get it right.

[@brian.d.mobley]

Good tips!

[@volkov6460]

Hi there mate, would there ever be a sort of this video for a 125cc pitbike engine? its the most common one and i really need help with mine

[@brian.d.mobley]

Hi Volkov. Which 125 motor are you referencing?

[@volkov6460]

@@brian.d.mobley The chinese 125cc engines , the ones that come with the standard pitbikes (thumpstar , stomp etc)

[@brian.d.mobley]

@@volkov6460 I would consider doing some videos on one of someone wanted to sponsor the build. I don’t have a bike to put that in, so I don’t see myself buying one.

[@volkov6460]

@@brian.d.mobley ​ @Brian D. Mobley I see, also do you have an explanation of how a clutch works on pitbikes? I dont understand how the little lipped cylinder can push the clutch plates out as it doesnt have anywhere to push on . If you do not understand what im refering to go to the timestamp 13:19 on this video "kzbin.info/www/bejne/f2aZfWijdrSnjKM" You see that black cylinder shaped thing? i do not understand how that works in engagement/disengagement Thanks!

[@rynophiliac]

you did a great job on this video. if you're looking for content ideas you could do some videos on specific bikes with specific problems and help diagnose the issues. for example 400ex has no spark - what to check and how to fix it. thanks for all the time that went into this video!

[@brian.d.mobley]

That’s a good idea. Troubleshooting videos. I’ve never done anything like that. Good tip! Thanks. And thanks for the kind words!

[@jentsevanmiltenburg8577]

This is awesome, very clear and comprehensive. Thank you so much. If anything I might add, maybe a list of tools needed 🤔 😁 Otherwise, awesome value. 👌

[@brian.d.mobley]

Hi Jentse! Thanks for the kind words. All of the special tools are listed in the description with links so you can buy them easily. Thanks for watching!

[@southtownloc_beats_4277]

Hello! Today I thought I broke my crank in my 2017 Apollo with a 124cc 154fmi motor. I tried to tighten my selector bolt but I overtightened it and broke it off 😔 alas I will do my best to extract the broken bolt and I’m stoked to have found this video, hoping it can aid me in my quest to rebuild my bikes engine.

[@brian.d.mobley]

Hi Olympic! What a bummer! I hope you can fix that broken bolt. Not sure if this video will help much, but I hope so! We’ve all dealt with setbacks like that, so just stick with it! You’ll get it fixed!

[@heydonray]

OUTSTANDING !

[@brian.d.mobley]

Thank you!

[@troyfred45]

Very well done video thanks Brian!

[@brian.d.mobley]

Hi Troy! Im so glad you found it useful! Thanks for watching.

[@nofunfilms8755]

Nice video man, doing an 01’ xr70 right now and this helps a ton

[@brian.d.mobley]

Thanks NoFun! Few things in life make me happier than knowing I was able to help someone with one of my videos! Thanks so much for watching and taking the time to leave s nice comment like this. You made my day!

[@bobwhite4344]

great vid. very professional.

[@brian.d.mobley]

That’s so nice of you! Thanks Bob. 🙏🏻

[@feasternate]

Very informative, thank you

[@brian.d.mobley]

Glad it helped you! Thanks for watching!

[@roblesjesse]

This video GREAT!! Thankyou very much my friend!!

[@brian.d.mobley]

Thank you! Wait until you see the final product. This bike is going to be hot!

[@BB-nn9en]

excellent video! Thanks

[@brian.d.mobley]

Thanks BB!

[@brotherkhan2885]

Great, very informative and very well detailed. Just what i needed.

[@brian.d.mobley]

Hey BrotherR! I’m so glad it helped. That was a big video to make. Lots to stuff in there so it was hard to make it a reasonable length. Thanks for watching!!

[@brotherkhan2885]

@@brian.d.mobley No problem buddy, i build these engines myself here in England and its pretty hard to find the torque specs for the bolts also it was very helpful that you mentioned the gear shift drum, was always something i had trouble with until watching the video.

[@brian.d.mobley]

@@brotherkhan2885 Thanks for the feedback! Im always curious to know if something in a video is of value to the viewer. I try to make them in such a way that it would be in an order and style that I could follow, but its not easy to make a video. Especially a big one like this with tons of info and not make it 45 minutes long!

[@brotherkhan2885]

@@brian.d.mobley Personally for me the longer the better, but then again you can always go back and fourth if you’ve missed anything. And whats happening with that Cr125 ?

[@brian.d.mobley]

@@brotherkhan2885 People can get bored, so I try to keep videos moving along briskly while not skipping any steps. It’s not easy! As for my 125, that is a shifter kart motor. I do have an 07 125, but the motor in that bike is still fresh. I’d love to do a good rebuild video on a 125 using my newer camera and lighting. And editing! I’m better at that now.

[@mikewalton5469]

very good video! thanks for sharing the information.

[@brian.d.mobley]

Thanks Mike! Glad it helped. Sorry I didn’t reply sooner. Somehow I missed your comment. Thanks for watching!

[@stephaniekane7276]

Great video

[@brian.d.mobley]

Thanks Stephanie! Glad to read that the fairer sex is putting the content to good use! Keep wrenching!!

[@stephaniekane7276]

85% of my knowledge come from KZbin when it comes to engines and such if I don’t have the manual or specs, On my first bike I actually did accidentally unbolt the tensioner, luckily it went back in no problem

[@brian.d.mobley]

@@stephaniekane7276 That is such an easy mistake to make! Glad it all went back together without issue!

[@stephaniekane7276]

Do you have an email address? I have a few issues with my pit bike engine I’d like your opinion on

[@brian.d.mobley]

@@stephaniekane7276 You can message me through Instagram. I'll try to help, but I've kind of given up diagnosing problems on bikes that I dont have in front of me. Instagram link is on the "homepage" of my KZbin channel. Or, search brian.d.mobley

[@brianseadoo8307]

Hi Brian , the sprocket I’m talking about is below stator plate, I would like to know how yow put this on crankshaft in the proper position, it is pressed on the crankshaft. The bike I bought had this removed. With no marks or scribes were it originally was. The crankshaft chain I believe is driven by this sprocket.

[@oniramos8187]

love your videos!

[@brian.d.mobley]

Thanks Oni! I have a few new ones coming out soon!

[@tomdalman5863]

I really appreciate your videos. I have searched all over the web and KZbin for an answer without success…. I have a Honda CRF50. When shifting from 1st to 2nd it really hits hard when the gear grabs. I’ve adjusted the clutch but it still really hits hard. Is this just how these bikes are or is there something else I should be looking into? The bike is fairly new with zero signs of abuse from the previous owner. Thanks for your help!

[@brian.d.mobley]

HI Tom. I have dealt with that issue on these Honda OHV engines also. The most common reasons for this are an overly tight shift drum bolt. (You can access this fairly easily under the ignition cover on the left side of the motor), bent shift forks (harder to get to!) and the shift fork pins (even harder to get to!). The good news is; the overly tight shift drum bolt is the most common reason and the easiest to access and fix. Thanks for the kind words and for watching!

[@tomdalman5863]

Thank you very much for the help. I’ll head out to the garage and work on it today!

[@JasonBohl]

What kit does tbolt sell that has the oil seals that go between the cylinder and trans And the cylinder to head? I've looked on their site and I'm not sure where to. Find them. You put them on at about 17:38 and 19:45. Also I have the 146 bbk and was wondering if the second seal you put on on the left side is necessary for my kit? It doesn't quite fit in the head gasket hole. The seals got crushed when I put the top end together and need to buy them separately but don't know the part number.

[@brian.d.mobley]

Hey Jason! Id recommend contact TBoltUSA directly and ask them. They know much more about parts availability than I do. And I’m not familiar with the 146 you reference. Again, the guys at TBoltUSA would probably be a better source of knowledge. Sorry I am not able to help more than that. Thank you for watching!

[@Bikebros27]

My lifan 110cc seems to slip on the kickstart press down on the kickstart. You can feel something slipped inside the engine. What do you think this could be many thanks

[@brian.d.mobley]

Maybe the clutch springs are overly preloaded. I’ve never worked on a Lifan, so I’m not really sure.

[@βασιληςκοντοπριας]

Excellent video!! Can you help me with one problem that i have ?? I have correct timing and when i turn the engine with hand i see from air valve that when go to close exhaust valve go to open!!so for same second are the both open!! Who can i solve this problem ??

[@brian.d.mobley]

HI! Unless you have changed your cam to some very unusual profile, this should not happen. The valves open and close in rapid succession, but both should not be open at the same time. This is highly unlikely. I go over the valve actuation in my most recent video on the subject of valve adjustment. Look for it; “2 Ways to Adjust Your Honda OHV Engine Valves.” Thank for watching!

[@davelowets]

This is called valve "Overlap", and almost all modern cam profiles have some. A performance cam WILL have a larger amount of overlap than a stock cam, but yes, they all have some. It's completely normal.

[@βασιληςκοντοπριας]

@@davelowets i find the problem and the problem is that the exhaust valve dont close well!!i must replace it with new one!!the engine is super cub 90 honda with 3 gears!!so its old one

[@davelowets]

@@βασιληςκοντοπριας Check your valve guides before you put a new valve in it.

[@connellhuilcapi3369]

Awesome video man!!! You have yourself a subscriber!

[@brian.d.mobley]

Thanks Connel! Glad you enjoy my work. Thanks for watching and subscribing!!

[@wranglermiguel6347]

What is the correct assembly of the crank case bolts being that their are 7 bolts and 3 different sizes?? I got the carb breather bolt 😂

[@brian.d.mobley]

It’s really hard to describe to which hole each bolt goes through. I have a picture I can email to you if you can’t figure it out.

[@bikemancody2752]

Very nice.

[@brian.d.mobley]

Thanks Bike Man!

[@k30mtb78]

Did your crank case gasket have a waxy feeling to it? I was debating whether to put assembly oil or oil in general on it before installing it

[@brian.d.mobley]

Hey K30! Gosh! I don’t recall any waxy feel, but I’m not sure. I doubt it would hurt regardless to rub the gasket with some assembly lube. It makes it easier to split the cases in the future if that becomes necessary. Thanks for watching.

[@wadelomas4543]

Back in the day....Powroll made titanium weights for the automatic clutch. Pretty cool. Higher rpm engagement and also acted like a lightened flywheel. Had this setup on an XR 70 my son flattracked as a kid.

[@Drain09]

What jetting did you use with a 88cc kit and uni air filter open system.

[@baileyteg1]

I think that depends where you live, elevation above sea level

[@brian.d.mobley]

Hey Jacob! So sorry buddy! I just dont recall. and I dont want to dig into the carb to go find out. But, if you need advice on jetting, contact TBoltUSA. They have more experience with that than anyone.

[@davelowets]

@@baileyteg1 Exactly correct... I never recommend using someone else's jet combo on a different machine. Too many variables involved.. Do it the right way, and do a plug chop, pull it, and read the plug. Jet it until the plug looks correct. Takes time, but it's the only sure-fire way to get it right.

[@chris117ize]

I've got a 92 z50 ,I have to split the case on. Are the internals the same?

[@chris117ize]

I realize the title says z50 just making sure

[@brian.d.mobley]

Hey Chris! Essentially, yes. The cylinder is smaller and the head is slightly different and the transmission is slightly different. But the differences are so small that it won’t affect the disassembly. Thanks for watching.

[@chris117ize]

@@brian.d.mobley thank you

[@richiecooke8866]

Hi there i think your video is brilliant I've got a problem with my gear selector drum bolt when I tighten it up i lose the gears but if I leave it lose I get them back any ideas please

[@brian.d.mobley]

Hey Richie! Honestly, I have had the same problem. That bolt is tricky. The way I have handled it is to start with the recommended torque spec and then just adjust the bolt tension based on how the gear selecting works. Usually a torque spec lower than recommended works better. Hope that helps.

[@richiecooke8866]

@@brian.d.mobley ok mate il try that thank you for your help much appreciated

[@zachdavis2641]

When setting the timing, my flywheel moves ever so slightly off of T when letting go of flywheel. Is that a problem? Piston stays at tdc when it does.

[@brian.d.mobley]

Hi Zach. That is totally normal and usually due to cylinder pressure. Good question!

[@zachdavis2641]

@@brian.d.mobley thanks for quick reply

[@brian.d.mobley]

@@zachdavis2641 My pleasure!

[@zachdavis2641]

@@brian.d.mobley another quick question. Should have asked with original question. Do I need to hold the flywheel at T while timing? Or just let the flywheel settle out of t position then set cam gear?

[@bradjenkins4319]

Damn I got a 1974 CT-70, can I send in the motor and have T Bolt rebuild it?

[@brian.d.mobley]

I don’t think they rebuild motors. Look up SoCalMinitrail on Instagram. They may be able to help.

[@christopherprice55]

Hi guys, is there anything I can use to flush out a stomp 140 engine please ???

[@brian.d.mobley]

Hi Chris. I don’t know what you mean by flush out. And I’m not familiar with a stomp engine. I wish I could help more.

[@christopherprice55]

@@brian.d.mobley flush the engine oil out ??

[@brian.d.mobley]

@@christopherprice55 Genrrally there is no need to do more than drain the oil. The drain plug is on the bottom of the motor.

[@MichelBakhos]

What’s easier putting a 4 speed or a manual clutch ? Thinking of putting a 4 speed to compliment my recently installed manual clutch but a little intimidated by the process ..

[@brian.d.mobley]

Honestly, I kind of said that wrong in the video. What I should have said was “manual” not “4 speed,” but I didn’t want to have to re record that whole intro. But, manual is (I think) better than centrifugal. But 4sp doesn’t make much difference. The 1st gear on a four speed is just a granny gear and 4th is similar to 3rd on a 3sp in terms of gear reduction.

[@gear1755]

Everytime i torque the transmission bolts it freezes up the transmission and wont let it shift, what am i doing wrong?

[@sethpetras6641]

Hey Brian loved the video I’m having an issue with my timing it’s either a tiny bit too high or a tiny bit too low even if I move it one tooth I already wrecked a set of valves because they were hitting the Wiesco forged piston I got for it which brings up the compression ratio by having a higher piston dome but it’s supposed to be compatible any chance you can give me some tips

[@brian.d.mobley]

Hey Seth. Its funny. People seem to only ask me the craziest and hardest to answer questions!! This is one for sure. Logically, I cant think of why this would happen. But, a few reasons why it may are: Somehow the keyway in the ignition is not lining up with the woodruff key or the woodruff key is missing. Someone tinkered with the cam wheel and bored out the mounting holes resulting in misalignment. The flywheel you are using is not made for your motor. The cam chain is worn out. The guide sprocket or guide roller is worn out. The cam chain tensioner is stuck and is not providing adequate tension to keep the chain from jumping a tooth on the crank. The piston is installed upside down (COMMON!!!). The wrong thickness head gasket was used. Thats about all I can think of....

[@sethpetras6641]

@@brian.d.mobley thanks for the tips I’m gonna check my cam chain and get the right bolts for the cam sprocket i used different ones but I installed the piston with the arrow pointing to the bottom/exhaust valve and I went but how the service manual told me to set the timing which is the same way you did it the woodruff key is fine And so it the tensioner

[@brian.d.mobley]

@@sethpetras6641 A friend of mine (Pete Andleman) who is brilliant about engines commented to me that your issue may be that your piston may not be compatible with your cam. Cutouts in the piston must be sized so that they are compatible with the cam being used.

[@sethpetras6641]

@@brian.d.mobley I would be surprised concerning that it’s the oem cam and it says it’s totally compatible

[@brian.d.mobley]

@@sethpetras6641 OK. I didn’t realize that about the cam. Just trying to think of anything you might look in to.

[@VINRAVY-z7o]

❤❤❤

[@brian.d.mobley]

Thanks!

[@sethpetras6641]

Hey when I tried rotating the Kickstarter spindle the crankshaft wouldn’t turn

[@davelowets]

Anti-seize..... Keep your fingers off is RIGHT! If you get a tiny little bit on your fingers when you use it, it WILL end up all OVER everything... I swear, I could paint an entire house with ONE little tube of the stuff. 😕

[@brian.d.mobley]

You are so right! I treat it like im handling plutonium or something every time I use it. The bummer thing is that its hands down one of the best substrate choices for so many applications that I find I need to use it regularly!

[@davelowets]

@@brian.d.mobley 😆 🍻

[@diyleather8126]

可惜我们国内没有老车文化！

[@brian.d.mobley]

Pity indeed!

[@NshsShdh-jx9ob]

👍👍👍👍♥️🥰

[@brian.d.mobley]

Thanks NSHS!

[@drmoose7233]

this is just great so clear with the explanation +1. good job man

[@brian.d.mobley]

Thanks DrMoose! Glad you found it useful. Thanks for taking the time to share the nice comment.

[@UserUser14880]

Is tbolt Parts Made in China?

[@brian.d.mobley]

I’m not sure.

[@NshsShdh-jx9ob]

🥰🥰🥰🥰♥️♥️♥️👍👍👍👍

[@brian.d.mobley]

Thanks

[@charlesdavidson7324]

👍🏽👍🏽

[@brian.d.mobley]

Thank you Charles! That was a hard video to make! Lots more coming so stay tuned!

[@charlesdavidson7324]

@@brian.d.mobley I most definitely will be staying tuned! I’m currently doing 3 builds at the moment. I just got a GoPro so I can start uploading content but I’m realizing editing is harder than it seems.

[@brian.d.mobley]

@@charlesdavidson7324 Editing is incredibly difficult. And, the more filming you do, the higher you tend to raise your expectations. Lighting and audio start to bug you if they aren’t perfect. On this engine video I probably have 60 hours of filming, script writing, editing and promotion. Its very hard to do it well and its never as good as you want. I recently made a 1:37 video showing the “After” of this bike build. That 1:37 clip took me 9 hours just to edit. The filming was probably another 3. I have a lot more respect for film makers nowadays!

[@kraigvanderwyk1153]

No mention of ring separation. 😒

[@brian.d.mobley]

17:09.

[@sharktooth99]

The ads make this video completely unwatchable

[@brian.d.mobley]

I just let KZbin decide where and when to put the ads, but they more than normal on this one. Not sure why. But I went in and manually removed two of them. Maybe since it is a new video they added more advertising than normal.

[@atcquad]

If you pay for the premium KZbin membership, you don’t get the adds!!!worth every penny!!!