Cafe Racer Forum banner

CB900 Cafe Racer project

91K views 493 replies 43 participants last post by  tjurek51 
#1 · (Edited)
Post 1: Land vehicle Vehicle Motorcycle Motor vehicle Automotive tire


This is a 1982 Honda cb900c and is the base of this project. while skeptical at first of the 9200 miles on the odometer, given the grime and stiffness, i think this is accurate. I chose the C platform for a couple of reasons, but primarily because of the longer frame. i'm 6'7" and want to extend the size to fit me wherever possible. However, this bike is friggin heavy. So, here's the plan; strip it down to the frame, literally. throw away those parts that are just too old, sell the parts i won't need (anyone interested, just let me know. i'll give you a great deal). replace the tranny with single stage, racing gears (no hi/lo, just straight shifting). replace the front fork, stainless brake lines, and of course the handle bars, fiberglass, etc. as for the back end; to cut weight, i was considering having a new swing arm fabricated to move the back wheel back and allow for a single rear shock v. the current dual air shock set up. anyone done this before? if so, i'd love to see pictures. i may also have the seat area lifted to, again, give me a little more room.

Folks, i know this will be a lot of work and a bunch of you will be tempted to say "scrap it" and "don't bother..." i'm new to a project like this, but have the time and money to make this a fun build. i look forward to asking your guidance through this journey and appreciate all the help i anticipate receiving from you far more experienced individuals.
 
See less See more
1
#66 ·
Those gator grip sockets are used to get wheel locks off where the owner lost the key. We used to call them the wheel theives master key.

Don't be shy, post up exactly what you spend on parts now that you have torn everything down. Either you are going to reuse 99% of it and wasted the effort just to do gaskets or you are doing a full tilt refresh and it's gonna cost. Let's see how much.

i can tell you you are at least going to have to buy new block studs because those are one time use only and if you don't replace them it will be harder to get the head and block to seal.
 
This post has been deleted
#67 ·
Help me understand the block stud comment? I've not found anywhere, even in the manuals or elsewhere online that these need to be replaced. If they're in good shape, as these appear to be, why replace them? what makes them a one time use? just trying to learn.

I do plan to post the parts list and cost. so far, only had to get a complete gasket and seal set, Primary counter shaft, replacement bolts set, handle bar and grips, carb rebuild kit, chemicals and rearset. not 99% but 90%.

- - - Updated - - -

mad skills. just sayin.
 
#68 ·
never mind on the stud question. after some searching I found this thread. http://forums.sohc4.net/index.php?topic=77878.0 . bottom line, the materials used on these studs are soft and once torqued and loosened loses it's tensile strength. this thread was very helpful so I post it here to help anyone else. off to buy new block studs. thanks Geeto67 for pointing me in the right direction. I need more of this type of help, so thanks again.
 
#77 ·
Fuck me Louise.... high school must have been really different east of the Ontario border. Anything useful must have been saved for the 13th year which we didn't have. You also must of had some edumicators and administrators with an IQ greater than their hat size.
 
#70 · (Edited)
Technically they are called Torque to Yield bolts, and almost every motorcycle engine uses them to secure the cylinder block to the head. They are used in high frequency high load situations where fatigue would otherwise be an issue.

Honda used to produce a general service manual or a tools service manual in addition to the model specific ones. They are much rarer but they cover things like theories behind how a carb mixes fuel and the various types of fasteners you find in an engine and how to use some of the special tools.

It's called the Honda Common Service manual:
http://www.motorcycles123.com/mc123_images/honda_common_service_manual_1.pdf

By the way, I believe the model specific service manual also covers the block studs being torque to yield so if you were reading your service manual you should have seen it. Other Torque to yield bolts are the connecting rod cap bolts so....proceed with caution. remember caps and rods are not interchangeable so if you take the rod off the crank make sure you mark the orientation and rod it goes to.

By the way, in terms of making it worth your while - in my mind you now need to at least replace the piston rings, hone the block, and replace the crank and cam bearings (if the crank and cam themselves are showing no serious wear). And you will have to "break the engine" in again.

One of the main points of my "Patina flip" thread was to show people that if you have a honda four that isn't showing signs of damage it's better to get it running and evaluate than take it apart. These bikes were way overbuilt so anybody who says "it's a smart idea to take the engine apart just because it is old and has been sitting" doesn't know what he is talking about.
 
#71 ·
thanks Geeto67, and you're correct, I don't know what i'm doing (thought that was clear, lol). I have the Clymer manual. it discusses the torque of the various bolts and how to inspect them, but that's about it. so I appreciate the additional manual. plan is to replace rings, for sure. cylinders are smooth and appear in good shape, but beyond visual inspection, not sure how to determine if they need to be honed. there's literally no burns, carbon or rust on them, nor any scratches or grooves beyond what (I believe) you'd expect to see. also, I wasn't going pull the rods off the Crank.

As for paying attention in HS, you all assume my HS had a teacher worth paying attention to.
 
#73 ·
thanks Geeto67, and you're correct, I don't know what i'm doing (thought that was clear, lol).
well we all have to start somewhere.

I have the Clymer manual. it discusses the torque of the various bolts and how to inspect them, but that's about it. so I appreciate the additional manual.
Even seasoned guys will sometimes tell you one manual is not enough when you are trying to learn. Get a haynes and also an original service manual. I think the original service manuals are available for download off cb1100f.net if you are a member.

plan is to replace rings, for sure. cylinders are smooth and appear in good shape, but beyond visual inspection, not sure how to determine if they need to be honed. there's literally no burns, carbon or rust on them, nor any scratches or grooves beyond what (I believe) you'd expect to see. also, I wasn't going pull the rods off the Crank.
as engines run in, the rings smooth the cylinder walls and that is how they seal. Sometimes they form a glaze as well. If you are replacing rings then the cylinders need a hone to scuff them up so the rings will wear in and seal. If you just put on new rings and don't scuff the cylinders the rings will never seal. A honed cylinder ready for rings looks like this:
Pipe Muffler Metal Auto part Cylinder

Get yourself a ball hone (a thing that attached to the end of a drill) and make a few passes each in the cylinders to scuff them up. 320 grit, about 2.5" should do it and use plenty of lube. Start spinning it before you put it in the bore and don't stop until after you have taken it out. you just need to scuff up the walls so make three plunges in and out and then evaluate. you can get overzealous and accidentally bore the hole bigger which you don't want to do. these are what ball hones look like:
Toilet brush Brush
 
#72 ·
Alright, after soaking the parts for a day, I got them mostly cleaned. however, there was a lot of carbon on the valves, as you can imagine. I wanted them clean to see how much of an edge I have on them and wanted to make sure I had a good surface for lapping, so I decided to get them clean to the metal. Someone suggested rust remover. as I didn't have that, nor wanted to make the trip into town to get it, AND having worked with Vinegar to remove rust in the past, I soaked them in Vinegar for 24+ or so hours. Here's what I got;
Wood Metal


Using a dremel tool to remove the carbon, it came off easily; like a cloud of dust. Auto part Tool


looking up close, I think I have a pretty good edge. a good lapping will hone and seal these good, I think. Metal


Until next time...
 
#76 · (Edited)
You'll notice in the photo of the cylinder that the hone marks run at about 45 degrees, which is what you want. In order to do this at home, your best bet is a strong variable speed drill that has an adjustment on the trigger to limit speed. To get the proper 45 degree cross hatch, you need to go slowly.... very slowly. I prefer rigid type hones, but that's another story. The ball hone will follow any out of round, taper, and tend to smooth out the edge of any ridge. You can use solvent as a lubricant, but be aware that it cuts faster. Whatever you do, clean the cylinders when you finish and when you think you have them clean... clean them again. Rub a clean dry paper towel in there and when it comes out perfectly clean, you are almost done. Might be an idea to pick up a knackered cylinder and practice first before you set out on a new adventure. Lack of deglazing (when its necessary), or doing it incorrectly can cause heartache.
 
#75 ·
Do you know if it will actually bolt into your cases? (what?) found a primary counter shaft and lined up to the rear sprocket in my existent rear wheel on a modified swingarm (see other posts). swing arm pivot is 3" back from the chain drive bike (as you see my 750 chain drive in my picture, I have a point of reference). according to the manuals, clutches are identical on both styles, as the only way the shaft drive works is with the addition of the sub transmission. all other gearing is identical, requiring identical clutch. clutch discs look clean and in good shape (from my limited knowledge and comparative pictures). only question I have now is what happens when I install a longer chain on this bike?
 
This post has been deleted
This post has been deleted
#79 ·
Pretty amazing that even when you may be right you still come across as a dick. I bet I have bored and honed eleventy billion cylinders so I know what I am doing too. Bottom line for me is that any reasonable crosshatch will work fine if you do a careful break-in of the engine. I have a little bit of experience building race engines and then racing them. I also have had a little experience checking race engines after racing them with diagnostics such as leak downs and such. Any reasonable crosshatch will do the job.

Now, to throw you a little bone, because I don't know for sure. I have never checked to see whether the angle of the crosshatch has an effect on HP, since I have not tried a variety of crosshatch angles abd tested it on a dyno. A certain angle may actually be better for theoretical HP. I suspect that it would only be significant on some of the more modern engines like an R^ or GSXR, where the quality of build for a legal Supersport engine makes a difference for a top level racer. I am pretty sure that it does not matter on an old aircooled bike for the street.
 
This post has been deleted
#80 ·
True enough, you do get politeness points for the "thanks" and I am sure he will see your input. I wonder how he will take it?
The whole break-in question a real shitstorm waiting to happen, cause nobody can agree on what is right or wrong. I sure don't break in a street motor the way I break in a race motor, but I have checked race motors after a 6hr endurance race on a fresh topend and break-in consisting of the practice sessions and had less than 2% leakage. Not how I would treat a fresh street motor, but we could get 20 endurance race hours and a bunch of practices and sprints before it needed rings and a valve job with a CBR600F and GSX600F motors.
 
  • Like
Reactions: pwalo and DohcBikes
#81 ·
If you follow the honing procedure that Cyorg posted, from Hastings mfg, you'll be fine. Do get a used cylinder to practice on, you want to take the minimum amount of material off the cylinder possible but still end with proper crosshatch. See if you can't find a Honda factory service manual for your bike, maybe on ebay.
 
#85 ·
320 or even up to 400. 220 is too aggressive for a newbie and makes it easier to screw it up. Maybe once you have honed a few try the 220 or a flat stone.


here is the 900c/900f suppliment to the factory service manual for 1981 cb750s. It won't have everything but it will have some things:
https://www.manualslib.com/manual/910149/Honda-Cb900c.html#manual

here is the 1980 900c full manual:
https://www.manualslib.com/manual/1002848/Honda-1980-Cb900c.html


Rings seat between 500 and 1500 miles. For the first time starting it, make sure you take it to operating temperature and ride it (don't just let it idle). Don't use more than 3/4 throttle. Take it up on the highway and accelerate to 70mph and then back to 55 then up to 70 and back to 55, don't let it just loaf along at a set rpm. Let the engine overrun, don't pull in the clutch when slowing down.
 
#83 ·
to answer the question, I pay attention to all of you. up front in this thread I mentioned I don't really care the tone as long as; a) it's useful; and b) I learn something (i.e. in the midst of you lighting me up, you actually articulate said "useful" point in a way I can understand.

I also openly admit I don't know what i'm doing. if that insults those who have done this a million times, I do give a $hit. i'm having a good time and sincerely appreciate all the input. having said that, is there a formula for breaking in the engine I need to follow. not a racing engine of course, and will use on the street. appreciate any direction on this one. thanks.
 
This post has been deleted
#87 ·
70 mph? That's not even the measurement of reference you should be using. Break in is about RPM, not MPH.
no, but it's an easy frame of reference for a newbie to remember. It's pretty easy to for someone to remember put the bike in top gear and accelerate up and then drop back, esp if they are conditioned to look at the speedo. Consider it a colloquial short cut that captures the spirit of the right way.

Rings are broken in WAY before 500 miles.
eh...some times. My Pontiac v8 took 1500 miles but I used moly rings in it. So did my 400ci chevy. For bikes, yeah they tend to seat faster because they run at higher rpm and have less surface area, but I usually do break ins to 1000 miles minimum just to be safe. Then again the last engine i broke in was in 2007 so maybe things have gotten better in 10 years.
 
#86 · (Edited)
Most OEM's and ring manufactures recommend a 45 degree crosshatch. It's a stock CB900 "C" , so there is a fairly good chance that 45 will be ok. 45 is roughly middle of the pack, but it's not a racing engine and it's not a Harley Davidson. You could also take into consideration that it came from the factory that way and they still use 45, when instructing at the Honda service schools (at least last time I checked anyway) albeit they are an OEM instructing techs to repair stock engines. However you approach it, take a look at the bottom of the liners and you will see some of the original factory cross hatch (assuming nobody was in there before you) and try to replicate that. Those fellows from Hamamatsu know what they are doing when it come to engine building. Try to keep it consistent. No stacking on the top or bottom.

As far as break-in, if you are just going to re-ring, then all you are really doing is bedding in the rings and not worrying about cams and bearings. Personally on a street bike, I don't really fret too much about it. Just follow what Geeto said. Keep in mind that the first thing that happened when it was new.... it was driven off the assembly line onto a set of rollers and nailed to the pin and run through the gears like it was stolen.
 
This post has been deleted
This post has been deleted
This post has been deleted
#100 ·
Just can't stop being a dick, can you? Why are you trying so hard to get everybody to believe you know what you are talking about, but it is all secret and you won't share? Dick moves all around. I think they are missing you at Do the Ton.
 
#92 ·
OP.. if you are foolish enough to still be around, once you've deglazed the cylinders, read up on piston ring installation. There is a few things you need to know, like after you set the end gap , some of the rings have to be installed right side up (look for the T or dot, etc depending on whose rings you buy. You don't want them shovelling all the oil into the combustion chambers; it makes a lot of smoke when that happens. The end gaps have to be staggered when they are installed on the piston. I won't get into how many degrees apart they have to be cause I wouldn't want this thread to turn into a shit show. Just keep them away from the thrust side. When you go to reassemble this thing, assuming you do, get some help. Reinstalling the cylinders is simple after you've done it a few times. You might also want to make sure there aren't any signs of oil leaking up the rear cylinder studs. The studs come close to the main oil gallery and some of the cases were a bit porous in that area, which allowed oil up the stud which in turn made people think the base gasket was leaking. If suspect, you can pull the rear studs, clean the threads (studs and case) with contact cleaner and reinstall with Loctite thread sealer. Don't remember the number, but it's white and smells bad.... and god forbid you have to remove a stud in the future,,, you can.

You would be wise to read the entire shop manual and if it's a Honda factory manual keep in mind it doesn't cover everything. The fellows that wrote it assume you already know your ass from a wooden spoon.
 
#93 ·
OP? hmmm. and curious, why do you all say "assuming [I'll] be around" in your posts. none of this frightens me. nor do the comments scare me off. actually, kinda funny to read, though not sure what the new ZX6 or the Old timers ride has anything to do with my project (cool bike by the way. too bad when I get on one of those it looks like a bear riding a circus bike). As for the staggering rings, and T's/dots, the Clymers manual discusses that in detail, so I appreciate you reinforcing it. stock studs had some white sealant in it, so I assumed i'd need some Loctite and sealant as well on the new studs I just received.

when I get some time to get back at it, i'll post some pictures and updates. thanks all.
 
#94 ·
OP= original poster...you. Assuming you'll be around, because most newbies are horrified and leave when the natives rush in to give you a "virtual" Brooklyn stomp and try to extrude you through the cafe racer.net sewer grate. I'm also assuming you actually get this thing running because it's easy to get in over your head and realize a CB900 C is not worth the aggravation. I'm not up to date on your plans with the final drive, but I recommend you stick with the stock setup and focus on getting this thing running and back on the road. The upside to this is if you do fuck it up, it's only a CB900 C and you can just call the knackers and have them haul it away.... no harm done and you've learned a bunch in the process.

As for the studs.. I recommended the Loctite thread sealant. Not Loctite and thread sealant. They just need the sealant where they go into the case and it's only needed on the rear ones.
I do have a question though.. Why are you replacing the studs (and for christ sake don't tell me to go back and read this fucking thread)?
 
This post has been deleted
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top