81' CM400 engine rebuild

Drey6

Over 1,000 Posts
So I have a friend that has rebuilt a few car engines and replaced a few parts on his CB750 coming over to give a hand in rebuilding my top end. I have a full gasket set, and am on the hunt for piston rings. Curious as to what else I should do while she is open? I purchased a hone, valve spring compressor and intend to inspect the valves to spec and check the condition along with the guides and rocker arm. Other than this what do you recommend I also do, and are piston rings such as these : http://bit.ly/PtHsYv okay? I should also mention I have attempted to replace the head gasket twice and both times had leaks afterwards so in a 3rd and final attempt I might as well do a full rebuild while I'm at it.

Trust me, I know a 3rd time sounds ridiculous. I feel pretty stupid as it is and have had nightmares over how I can't seem to get this right.

As always, thanks.
 
Re: 81' CM400 top end rebuild

If you are getting leaks the head might be warped. If you have feelers check it per the manual and if not a machine shop should be able to help you out.
 
81' CM400 top end rebuild

(Forgot to mention a valve inspection and a valve lap is in order as well)

As far as the head goes, I have feelers and I intended to check that as well. Will make a trip to the shop to double check anyways. Sound like I'm missing anything else? Other than the head, can the cylinder head have a warp as well?
 
81' CM400 top end rebuild

Alrighty, I guess I'll do a write up as I go along so when some other dumbass (only insulting myself) is going back or doing this for the first time they have something to follow along with the factory service manual. Also, If I may not that this can all be done while the engine is in the frame. My bike just happens to be a drive away where it is stored so it's easier to bring it back so I can take my time and piece at it wherever I want.

CRITIQUES AND INPUT WELCOME.

Here is a link to a FREE Factory service manual (FSM)

http://www.mediafire.com/?cnkmdznfjgz

I started off by draining all of the oil and removing the oil filter ( filter was replaced recently, but for $7.00 I'll replace it while I'm doing all this) after I put the drain bolt back in and also the oil filter case .

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Next, remove the two valve cover bolts. ( bad picture, sorry)

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Then turn the flywheel to "T" which is top dead center to align the cam sprocket bolts horizontally once the rocker arms are removed.

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Now remove the 8 head bolts and remove the 2 rocker arm assemblies.
**be sure to not misplace or lose the dowel sleeves **

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Proceed in removing the first cam sprocket bolt; rotate 180 degrees with flywheel and remove the other.

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Now wiggle, ever so gently on the sprocket forward away from the mount and from here you will slowly remove the cam. Now remove the sprocket and slide a piece of wire to hold the chain up and to keep it from dropping in the case. (All should and will be inspected upon reassembly)

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Next to the back of the head to remove the tensioner adjust nut and washer and also the adjuster screw and washer.

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Remove the head, head gasket and place the head somewhere safe on a shelf or anywhere where it won't be dropped. At this point the cam chain guide (exhaust side can be removed)

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Stuff a shop towel in the center of the head and remove the cotter key from the rear tensioner and pin.
Remove tensioner hardware.

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Now I got stuck here for a moment because the cylinder head wouldn't simply pull free like the manual displays. Longdistancerider on hondatwins pointed out the ridges under the bottom to use for gently prying. Below is a pic that he took for someone on another thread. He is pointing it out for you.

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Now with the head free, gently remove it from the pistons and be sure to keep ahold of the cam chain. Set the cylinder head somewhere safe. Stuff rags around the rods to avoid foreign objects from entering the engine. I removed the top and middle piston rings and called it quits for today. Cylinder walls look good and will only need a hone from what I can see.(no pitting and no catching when I checked for smoothness).

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So here are a few questions. My shotty' paint job is even worse now from the oil leak and am wondering if this part is going smoothly, should I do a full disassemble and have all the cases and heads soda blasted for a clean rebuild? Cause frankly I'm done with paint.

Also, thanks for reading. Hopefully when this thread is complete. It will help some others out someday.
 
81' CM400 top end rebuild

Piston rings came in. Below are the oil ring and the two that surround it.

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But can't identify which of these is the top and the which is the second from top. Both say top and identify the top of each ring but the one on the left is shiny and smooth and the one on the right is black with a shiny edge and is more course feeling and is dark. Anyone know which is first, forgot to check the top two when I removed mine.

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Re: 81' CM400 top end rebuild

Wow, you are posting this just in time for me! I had a ring break on my cm and planned on doing a whole rebuild. Having never done one these pictures are sure going to come in handy. I have already ordered the gasket set off and Clymer just because I am one of those people likes a book in hand verses a pdf on my phone or tablet. Keep up the awesome work!
 
81' CM400 top end rebuild

Clymers are good but people have found discrepancies so double check torque specs.

I'll do more this week as all parts and tools have arrived. I may split the cases to inspect bearings and the transmission, maybe replace clutch plates too.
 
81' CM400 top end rebuild

I decided I'm going to split the cases and have them blasted and either powdered, just plain aluminum or maybe paint just the heads.

Started by removing the pistons from the rod. Used pliers to pull 1 clip out of each piston.

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Pushed the pin the out the same side of the removed clip and took out the other clip off of the piston while it was removed from rod.

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Next I moved to the flywheel. 18 mm bolt I believe (can't remember). Normal thread pattern and I used the clutch/flywheel tool (glorified vice grips) to keep the flywheel from turning the engine.

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Used the normal thread flywheel puller, glorified vice grips and a 21mm? socket to remove the reverse threaded flywheel. Was a little tough but be sure to use penetrating oil on the both sets of threads before use.

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Next I used the (little) handy impact drill to remove the three Phillips head screws that hold the stator plate. Not even possible by hand with a screw driver without ruining the heads.

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Next the two screws holding the ignition pick up and the Phillips screw above the sprocket that holds the wire clamp

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That's all for now, I'm late for work :)
 
81' CM400 top end rebuild

Now to the other side.

Removed the clutch side case cover. 13 bolts

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Remove the boot that covers the bolt holding the wire to the oil pressure sending switch.

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Remove the 4 bolts that hold that hold the lifter plate. Manual says in a criss-cross pattern. I used the clutch holding tool here as well.

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There is a lock nut and then the lockwasher behind that holding the basket in place.

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Basket is free. Also a bushing and the thrust washer behind that.

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I'm going to go through the clutch later to inspect the plates and springs to spec so for now I removed it all as one.
 
81' CM400 top end rebuild

Loosen the bolt holding the detent arm by 4 turns or so. Flip that arm (pawl) off of the cam plate and disengage the spring.
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Now if you haven't removed your shift lever from the other side yet, do so now. Push that through and pull the assembly out of the clutch side.

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Next remove the bolt holding the cam plate.

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Now remove the bolt holding the final drive gear, remove the gear and the chain.

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Now below that remove the snap ring (clip) that holds the gear to the shaft and remove the the gear. Then the 4 screws with an impact gun, again.

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The manual states to also remove the old gasket but mine wasn't there. However, I do have a few in my gasket kits when I reassemble.
 
I also split the cases the other day and I must say I am pleased with how well the bearings and gears look. Still replacing the bearings anyway with the mindset that I "might as well" since she is opened up.

So here is my next inexperienced write up on how this went.

Since the cam tensioner blade is held captive in the cases you will have to remove the case bolts in the way it is pictured.
**Older models and possibly some newer (like the SC series 450's) may have the blade in a position to remove through the top, but this model isn't set up that way.**

Anywho, you will have to remove the case bolts (16 bolts, I believe) and the starter to split the cases.

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Relatively clean aside from some old murky oil siting at the bottom of the case. The two large bearings on the input and output transmission drives are bearing #6305 and are available from Honda still for around $30 a piece... But through bothering Longdistancerider (the CM Guru) on Hondatwins a lot these past few days and reading up on bearings (truly riveting research ;) ), I guess these bearings aren't all Honda specific and the two mentioned above are available from the original manufacturer Honda used and many others would work fine in this application for about $10 a piece. Now the main bearings and the smaller transmission shaft bearings are only available from Honda and some discontinued parts are available from
http://www.davidsilverspares.com

Here are the large bearings I am referring to

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And the two smaller bearings

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I also forgot to mention that I am attempting to get my hands on a 78/79' 400 kicker shaft, assembly and the right case cover. So if I can get all that I can install a kickstarter since the crankcase is still set up internally for one.
Here is a write up on the swap from Hondatwins
http://www.hondatwins.net/forums/62-engine-discussion/19065-kick-starters-how-add-one.html
 
So I've scored the whole kick assembly from eBay and a case that is in decent shape. All I need now is a kicker arm and that can be had after I put her back together.

So now I need to disassemble the rest. Clean all the parts, take the cases,case covers, head and valve cover to be soda blasted. I think I'm going to polish the case covers and valve cover. Then paint the head black (possibly powder coat) and either leave the fins painted or have them sanded back to the aluminum.

Then install new bearings and o-rings on the bottom end and get this bitch back in the frame to break her in.
 
Alrighty then. My newly purchased 750 wa being a dick having a good amount of charging issues but that's all been worked out so back to this.

Back to the bottom end.
Remove the two bolts holding the oil strainer in place.

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Remove the 7 bolts securing the main bearing cap assembly.

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Remove the pin that holds the rear balancer and pull out the crankshaft assembly.

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What seems to be a part of a chain guard(don't know the exact name) need to be removed so the main shaft can be removed

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Next you can remove the tensioner that has been held captive.

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Next remove the pin and spring on the front counter balance shaft. Then the two nuts securing the shaft, balancer and gear in place.

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Now down to the gearshift drum and forks. Remove the bolt holding the detent arm and the 3 screws holding the bearing plate in place. Ended up using a impact on the screw.

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Remove the gear,forks and arm.

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I forgot to remove the oil pressure switch and found that removing it with a faucet wrench was the easiest.

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Also, remove the oil control orfices before blasting the cases. If you are just reassembling then just be sure that carb cleaner/brake cleaner makes it through with no problem before hitting the parts washer and reassembling.
 
Used my valve spring compressor for the first time and it is pretty self explanatory. It works great too.

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Removed the stem seals starting with the rings and removed those gently with a pick. Then removed the seal with a pair of wide lineman pliers. They came of with little pressure.

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An exhaust stud broke off so I am going to have a machine shop tackle that for me and I need to tap the cylinder two spark plug threads. A few are buggered up at the top. Then I can finally get everything blasted, new bearings pressed on and can move forward with this.
 
Finally getting back to this.

Since my last post forever ago, I had everything soda blasted. For paint removal, it was brilliant, when it came to taping threads...
Thank God I have a large utility sink, it made post-soda cleaning manageable.

Soda blaster dude and his set up. Also my little set-up for the past few months.

A shot of what I used to get old Hondabond off. Also a picture of me tapping 1 of what felt like 1,000 threads...did not have time to count each individual thread for accuracy.
 

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Figured now that the head is clean I'd check for any possible warping. Followed this pattern, here are a few pic's.
Used a feeler gauge (specs in the manual) and an el cheapo iGaging straight edge from eBay. Came in a nice soft case and is true (I compared it to another).
 

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Most recently started taping/ filling holes to prep for paint. Most likely will have to wait till Wednesday when humidity/temperature goes down... Maybe even Thursday. She will get an acetone rub down and an air compressor treatment before rattle can bonanza begins.
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Humidity was right at 60(max on the can instructions) today and I've put this off long enough.... So I said, "Fuck it" and finally spray bombed the cases. Cleaned with acetone before. Let that dry for about 10-15 minutes.

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Then sprayed 2 light coats with Dupli-color's gloss black engine enamel. Followed by 4 more medium coats of the same stuff and called it a day. Not too shabby for $7.50.

Top half turned out best of the two pieces.
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Bottom half showing some orange peel between the fins and the aluminum imperfections became more obvious after paint(on the top of the photo below motor mount, to the right).
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I'm okay with it overall. As long as it's coated and what's visible doesn't look horrendous, then I'm fine with that.
I know, setting the bar real high...
I plan to leave it be for a few days/week before I remove the tape... ever so gently!

I leave for vacation in 3 weeks, so I'll be attempting to make as much dough as I can and will get back to this if I have time. If not, it'll be here when I return.
 
To avoid any more future frustrations with leaking head gaskets (were they leaking oil pressure?), after inspecting for any small scrapes or surface irregularities aside from checking for warpage, try using permatex copper coat type head gasket spray. Mask off the cylinder bore, painted portions of block & head, mask off combustion chamber, hang head gasket from a wire/string/coat hanger overhead, and follow the instructions - 2 light coats per surface with 15 minutes in between. Do this right before assembly.

And I only ever really trust OEM head & base gaskets for the most part, as well as block oil passage o-ring and cam chain tunnel o-rings.
 
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