Honda C90 engine teardown - Part 1 

Brings back many happy memories Matt. First bike at 17 in 197?. First bike I ever worked on properly - because it had to work well enough to get me to work. First bike I ever tuned - with a lot of advice from my Dad. He was brilliant with all types of engines, even ones he'd never seen before. Following my Dad's advice to the letter, I polished the inlets, outlets, combustion chamber and piston crown. Then I reseated the valves. And just as I was ready to put the bugger back together, my Dad asked how much slack there was in the cam chain tensioner. He said he was concerned I might have reduced the compression ratio a bit. We both knew he was joking. At the strip down stage we had already established there was a ton of clearance between the open valves and the piston crown - by putting little lumps of plastacene on the piston. This was the beginning of turning my 1968 C50 into a Fizzer beater. We set off first to the glass wholesaler to get a few squares of thick float glass. Then to the panel beaters and paint spray suppliers to get a few grades of Emery cloth and coarse wet and dry. The plan of course was to remove 1mm from the head. Not an easy task to do accurately using this method, but it had worked on a pushrod Velocette several decades before, we saw no reason why it shouldn't work now. A few hours later it was done. I washed the head in paraffin and petrol to get rid of all traces of grit. The rebuild began on the Sunday morning. The adjustments to the timing were done by lunch, and the engine was back in and re-lubed by tea time. The baffle came out of the back of the silencer, and the brakes were looked at. Oh and I played with the carb settings a bit to get it to run just right. Result? Slightly harder to start, from cold smoother running, Much improved acceleration, a healthier noise and about 5-6mph on the top end. Depending upon who's speedo you believed, after downward adjustment, this meant 55-58mph! I had mates with YDS7, Suzi 250d, BSA Starfire, and all the mopeds of the day from Honda SS50s and Yam FS1Es, to Puch the more exotic Gileras and Fantic etc. They called me a gay old man for riding a Honda step through. But I beat nearly all of them. The Gilera was very quick though, as was another Italian or Spanish thing I can't recall the name of. Morbidelli? That was essentially a race bike. Best engine ever made. And yes, of course the fucking points go in there! Have you never worked on a '70s Honda before? Build it into a lightweight frame and race the bugger ;)))

When i was about 12, I had an old C90 we used to rag around fields etc, it was permanently stuck on full throttle (didnt know how to fix carbs back then lol) so we just used the key to control it. One day my mate was on it, flat out across a field with a big ditch at the end, just before meeting a road. The key popped out of the ignition as he was doing about 50 towards the ditch, he bailed off and Ghostied the bike into the ditch, it hit the other side so hard it snapped in half and the engine flew about 15 feet in the air. Always had more fun on banged up old mopeds than anything else.

Many many years ago, (the 80's) when boys were still tort mechanical design and engineering in high school as a matter of course, are teacher told us that the Honda Cub engine was the greatest peace of engine design ever. He then when on for the hole two hour lesson to tell us, in minute detail, exactly why as he dismantled one. As, at the time, I was a teenager who was constantly devising new and interesting ways to get a detention on the same day as D.E., I didn't listen to a word of it. Why did I want detention? Miss Chan and the chance to glimpse a stocking top. Thursday's detention was always very popular with the boys!

thanks Matt! great video, a fun project, looking forward to the next installments!

I've got a late '69 engine out of a ct90 I ended up replacing with a ATC125 engine. That cover on the head is for the points/cdi pick up on later models.

Hey Matt, here's a story for ya. As a newbie biker of only 2 years experience it has dawned on me that my YZF (that has been active all year round and lives in the rain,) is falling apart faster than I can afford to fix it. Cue youtube to the rescue and after an intense 3 days of binge watching I took my first steps in bike mechanical maintenance... I bought tools. I cleaned my brake calipers, followed by bleeding the brakes. I gave myself a hearty slap on the back for a job well done and being all manly and shit. Then I found your channel, did more research and realised that Tomorrow I'll be taking those calipers off again to remove the copper grease. Cheers Del. Seriously though Matt. Thanks for clearing that up. The Legend of copper grease runs deep. Everywhere tells you to use it.

Thank fuck for RU-vid I have just bought a c90 so your videos will be great for me to watch, cheers pal.

thanks for the informative video and colorful commentary !

Electronic ignition sits on the end of the cam shaft. Little pin holds it in place nut and washer holds it in place. It used to be points

Brilliant! I almost felt like I was doing it myself! All the cussing and swearing went very well with the beer I was having while watching this!

Yeah boy awesome video mate, those Honda 90 and 110cc engines are great. Can't wait for part two. Id love to see you tear down and rebuild a Yamaha YZF/WRF 400/426/450 engine, I love that Yamaha five valve engine.

When your rebuilding don't forget to use copper grease on the crank bearings and cylinder walls to stop squeals!!

Hope this tear down continues, I have 4 of these (2x125’s & 2x90’s) for my grandsons speedway bikes, albeit Chinese clones, of which there are probably more of than there are Honda’s

i love this little lump i have a honda msx125 it can trace its roots back to this i believe? looking forward to the next part mat

Please do a video on the clutch. It's quite an interesting and clever design.

I'm currently restoring one, Thanks for the information.

In this installment, matt tries to wrestle an inanimate object... and loses

that copper washer in the front is standart matt ;)

quick question about boxer engines or engines laying over like this. does one side (bottom side closest to the ground) of the piston/rings wear out a bit faster?

Amazing intro!;) ....I hate regular screws on engines. Had an engine once, and I wanted to take the clutch cover off... all screws were destroyed (before I got it). I need a hammer impact screwdriver thingy.. I want hex stuff on an engine. Everywhere.

4:07 and 15:22 That stud does feed oil to the top end. It originally had the domed nut at the top along with the copper washer to seal the oil. The missing part in the section you removed before getting to the cam chain is the automatic timing advance mechanism.

this take's me back first bike engine i had apart. first ever mod was fit a RD 50 M K&N to it LOL

I've got a 1964 Cub C100 (50cc, pushrod) in the garage. It's a little jewel. 6v electrics, happily starts with a flat battery. I must take it for an MOT and then ride it around just to make me smile.

I have a 1964 50 cc motor you can have mate how do I get in touch to send it to you?

Nice stuff. Loving the greasy bits. Seeing those marks on your cam makes me a bit sad. When I did the rebuild on an m20b20 engine some dickhead also previously worked on the rocker shafts with a wrench. Those shafts and rockers were an absolute pain to remove because of the scoring.

Quick question, is my Honda C70 engine supposed to turn freely backwards when I turn the magneto counterclockwise?

A few mates had them, C70s and 50s too. I had an H100S.

They put these engines in so many different frames, I rode a CT70 and then an ST90, both had basically that engine, just with different displacement and gearing. They're as bulletproof as the early XL/XR engines, my friends and I ran the CT, ST, and an 83' XL124s hard for years and they never gave us problems like the newer bikes we got later. Honda used to make some seriously hard to break stuff.

workshop matt just about master of the zoom

I have a 1969 Honda s90, that's why I'm watching this video, I'm trying to learn how to fix it

When rebuilding make sure you get the right piston. Honda have many different shaped domes/heads for those c90 engines. I have been caught out before with a ct90 when running the piston was slightly hitting the head.

What could it mean if i can’t feel any air displacement from the spark plug hole whilst kicking it? I’m thinking about getting this cub working but Not sure how much work it is

nice to see a tare down hope you complete it please

bulletproof design, and the C50 was the first bike I popped a wheelie on ! (and the first bike i was pulled over on..."Barry Sheene are we....In a hurry are we sir....")

Back in 1995 my best mate brought a crunch 90 off another mate for 10 Lambert and butler and a teenth!! ....oh to be 15 again with contraband as currency!

How to differentiate between 12v and 6v system on this hondas

How many engines can run in this state ? Made In Japan

You could get a pitbike roller cheap to bolt the motor in to. I use to have a road legal 120 pitbike did about 50mph flat out good fun on the back roads

I'm liking this

The most fun you can have on 2 wheels period

The engine that made Honda

As subtle with tools as the Yorkshire ripper.

I’m hooked 👍

Good one.

That copper washer on the head bolt is there for a reason. Not a mistake by a previous owner. If you know, you know 😉

I thought this was going to go on a little longer when it just ends. You bloody tease!

My very first bike as an 8yr old learnt loads from striping down a c90 engine. Not the cub mine was a 1973.

My c90 has sat idle in my garage since 1989

Those marks on the camshaft may have been from someone trying to hold it with a pipe wrench while trying to crack the timing chain gear bolts loose. Pro tip, use the impact gun for those bolts. They'll back right out without trying to rotate the cam gear.

Those engines were almost bullet proof, one of the first bikes I road was an early 70's CL70. we had a shop full of the mid to late 60's and early 70's of those style of engines ranging from 60cc up to 70cc. Bunch of kids I knew had the old trail 70cc and 90cc bikes.

That looks like a pretty big combustion chamber for 90cc. Now I'm quite curious what the static comp-ratio is on these, maybe one of the key reliability features is that hemi along with a rather low compression ratio.

Mines a 1983 C90G, one of the very 1st 12v models and the very last exported ones made in Japan. Just thought I'd throw out a bit of what i know about these engines for anyone whos interested. -The C90E designation is just an iteration and doesn't mean economy. Also the letters aren't done in any particular order. -All the engines originally have one copper washer in the bottom left cylinder stud while the rest are steel (not sure why). -Some engines had the points on the side of the cylinder head but as far as I know a lot more of them had them in the left hand stator area. -Later model camshafts for the 12v ones used ballbearings instead of plain bearings.

Proof that event matt doesn't now everything

Sir may ask something, how to convert 90cc platino to cdi? Thanks

I thought everyone into motorcycles have or had one. I had many. My 1969 trail 90 blew the plug out of the head on a long trail ride and i hammered a block of wood in between the head and plug. It survived for a year that way until (I as a poor 11-12 year old who had to pay my own way) could rebuild the engine. I bet it would of lasted longer hahaha.

Something was there is an 'ignition' timing device.

Classy 😎

great!

finally . back to some real work

The points, or CDI trigger in the case of the Xl185 I had which had a similar head) shoud've been under that cover, someone's removed it & not put it back.

I need to get one of these old footballs to monkey around with. Looks like so much fun.

Properly running when run off a dock, reminds me of early days. someone tried hard at it with not a clue in the world.

One of the most reliable motorcycle engine designs out there! Me and my old man rebuilt a Honda Mini-trail 50cc engine because it was tired and low on power (it still ran) and on inspection we found that the oil pump had seized and the timing chain had worn away half the oil pump drive sprocket!!! We couldn't afford genuine gaskets so we cut out some gaskets from a cereal box and they worked fine for the rest of the time I had the bike with no leaks and we even took the bike around Australia for 4 months with us when I was a kid :) That bike has been through multiple generations of kids and adults and is still probably running to this day :) Such amazing reliable engines and if you've ever had one or worked on one I'm sure you'd agree :) P.S. Under that cover was the points plate and behind that a mechanical ignition advance cam runs on the camshaft with weights that throw out as the engine increases revs and it changes the cam position which in turn changes when the points open and close advancing the ignition timing.

As a nipper i was told that the corroded alloy comes apart easier if you have a hot steaming piss over it.

what bit was on the impact? Got some simmulair fucked screws on the sprocket cover of the GS500 i recently bought, wanna try to get them out decently before going to drilling them out. Cause that bit seems to work magic! Also looking forward to the other parts!

I think some of the earliest c90 engines had a pushrods instead of OHC.

I had a mustard/beige 90 and a blue 70, i used to go for miles on my 70, my first road bike was a Honda ss50 when i was 16, have you seen the street cub builds?

The points and back plate is missing out of that cover on the head Matt

I love. The. Honda motor own a early 60s S90. I beleive the engine is listed in World records as the Worlds most produced small engine of all time mine is actually on the original motorcycle. That has been stored indoors since the sixties as my Dad bought the bike but did not ride it as he intended to ?

finally a proper motor

Mine stopped running im gonna have to send it to a shop to get it running I'm sad tho I love riding my 68

Honda has built over 100 Million CK-90 or Cub motorbikes There is a Man from the UK has RU-vid channel CK-90 Adventure has ridden CK-90's all over the World rebuilds them on the side of the road. I took a 1972 Honda SL 125 motor .. bored & stroked to 160 CC's Powroll ported the head reground cam shaft .. I used the 24 MM Mikuni off from my GYT Kit Yamaha 80 then I put that motor into a 1977 Honda CR 125 frame .. about two years after I build my 4 stoke Dirt Bike Honda came out with the XR-200 4 valve head shorter stroke bigger bore more high rpm motor .. My points ignition has no spark .. I am looking for a CDI for it .. I had to run a battery as it is now ..

did you get that from delboy ?

Tough? We wired one wide open in neutral and left it, it stopped after 45 minutes but only because the wiring to the ignition melted, we stripped it down and mechanically it was still golden.

Good practice to place a cloth under the engine so screws dont bounce on the floor. Stuck gaskets: use a razor blade to cut the paper at least 1/2 way round then tap a thin screwdriver in to separate the cap. Use magnetic trays to keep track of parts.

What happened to the shit Chinese engine teardown with Isaac

Fuck all those screws, they look like they could turn things into a fucking nightmare real quick..

My 1971 C90 is smoking like an absolute bastard when it revs, fancy having a look at it for us?

left a shitty comment last week matt i apologies great video this one 👍

Damn didn't expect those screws to go out that easy. What Ryobi impact screwdriver is that? any other recommendations?

Fuckin' love the cub. First "real" motorbike I ever had, passed my test on it. Remember going to the MCN bash in Peterborough back in the 80s, they had a competition to win - umm - fucked if I can remember, some sportbike or other, but the competition involved a cub with all the oil drained out of it, you got 10 minutes thrashing the thing round a field and the one who melted it won the prize. It lasted 2 days of fat cunts running it flat out with no oil. Mine broke down on the A4 once, I got towed 40 miles by a madman on a Z900. Rope on the bars, hang on for dear life. Fastest the damn thing ever went, but not an experience I want to relive.

old used philips screws suck so much

Two questions. 1. What's a torque gun? It sounds different to an impact driver / wrench. 2. What kind of bit did you use in it? Or was it just an Easy Out type thing?

Can we see the primary chain & synchros pleases ? :P

I was making food for a vegetarian friend of mine yesterday and when cooking instead of thinking "wait, vegetarian or vegan?" while reaching for butter, my brain went "is butter meat?"

I have a c90 with an inspection sticker from 1968. It ran and would drive but after about 2-3 minutes it would get hot as hell and start knockin like hell. I have taken it to a few people and they dont know whats up with it. I am planning to tear it down and rebuild it. Im using your video as reference. Would be happen to share pics with you to compare as you mentioned in this video

hemi? PERK!!! LOL, I pulled one of these apart for a coworker in the late 70's, who bought it from a guy who assured him it ran, when he dropped it off and told him the thing was seized he asked me to do what i can, well when I pulled the cylinder off, the piston came off with it, the rod had snapped at the wrist pin when the piston was at tdc and totally wrecked the case, looked as if it had never seen a drop of oil (oiling hole was never drilled in the piston rod) I think we paid like $25? for a replacement used engine/w wrecked bike included ;-) from a local junker, that thing got him to work for years! almost 30 miles a day

Those "Phillips" screws aren't actually "Phillips" rather JIS screws. JIS is the Japanese version of screws and drivers. Over years of people mistakenly using Phillip's head tools on them...they strip.

More of these kind of videos (where you tear shit open) m8 they're interesting as fuck!

Clutch isn't centrifugal, it's operated by the gear shift, as the gear shift linkage moves, it engages/disengages the clutch Copper washer is on one head bolt, as it's to seal the oil gallery from the oil pump to the head That's a 6v engine so it's has points on the head. Later 12v engines have CDI ignition with a trigger coil on the flywheel. Are you using a JIS screwdriver bit? Honda use JIS not Philips, Philips/Posidrive cam out in JIS fasteners. That's not the cam chain tensioner, it's the guide sprocket, the tensioner is next to the oil drain on engines with the hydraulic tensioner. Fin rot on the bottom of the cylinder is normal, doesn't mean water has got in the engine, it's caused be road muck spraying on the bottom of the cylinder.

yeah!!! i need to repair one is detroyed and abondoned sooo thanks and dont dare left the serie video whithout finish! sorry mi englhis still a really crap state.

I tell ya what mate if you use a bigger ratchet it might be a bit easier to undo them 10mm bolts lol

One of these tried to kill me back in the 70's.the engine maybe brilliant but the bikes they put them in weren't,the Honda trail 90 I was riding(not my bike)has no real suspension in front despite the word trail on the bike.i tried to jump over a small ditch at say 40mph.worst beating i ever took.the bike was fine though LOL.

I like C90's clutch with steel balls 😂

JIS screws are always destroyed as 99% used Philips or even pozi drivers back in the day and they always cammed out rather than turn the screw.

Nem bírtam végignézni! A gumikalapácsos, csavarhúzóval feszegetős résznél besokalltam! :-(

yeah my hemi does 115 mpg...

Someone's nicked your ignition. There should be points, points cam etc under that left hand cover on the head. Get a socket adapter for your rattle gun. It would have made short work of those timing sprocket bolts. At one point I had about half a dozen 50s and 70s. Over time the auto clutches wear and start sticking. One I had was pretty bad so I ended up converting it to a normal hand clutch with mostly just basic workshop tools, apart from the release fork I made up which I had to weld. It worked rather well. The only issue was a bit of an oil leak as I didn't have a proper oil seal where the release pivot came out through the clutch cover.

Did you know that Jawa took Honda to court in 1966 because Honda had exactly copied and produced the automatic clutch / gear (Blatant patent infringement)?? In 1966 the world's biggest motorcycle manufacturer with Honda then second so it was the big boys going head to head in court. The case created a legal precedent and is referred to as "The Case of the Clutch - Jawa versus Honda" in law books. In the end Honda apologised and settled out of court agreeing to pay royalties to Jawa for every motor Honda sold with the Jawa system installed. Since then Honda and Jawa have become friendly and their engineers have collaborated on various research projects. One example is the Honda DN01 automatic cruiser motorcycle that saw the Czech engineers who created the Babetta 50cc 2 speed fully automatic self shifting gearbox working for Honda R&D. (Something for the Workshop to explain, though the Del Boy version would have more comedy value.....) I've rebuilt Honda Cub motors in the past and they're quite mechanic friendly. With a friend, we designed a sliding camshaft tapered cam lobed variable valve timing prototype on a Honda C90 engine back in 2004, approached General Motors and were told in a letter that, "GM can see no requirement or future in variable valve timing 4 cycle engines". When Suzuki announced a very close but inferior system 2 years later we gave up. Ours was better though as it used a cyclic rack instead of a second shaft and guide forks.

The Camshaft CAMe out dairly easily XD