79 engine rebuild

Hey, what projects are you planning or preparing for? CBX, other motos, workshop, WHATEVAH!
Post Reply
User avatar
wyly
ICOA Member
ICOA Member
Posts: 1727
Joined: Tue Oct 30, 2007 4:20 pm
Location: calgary alberta canada
Location: Calgary Canada

79 engine rebuild

Post by wyly »

It was one of those "that'll never happen to my bike" disasters that we've all seen pictures of, broken rod, hole in crankcase, cylinder head that looks like hamburger...then it happened to me :( ...why it happened I'll probably never know, it's very possible the previous engine re-builder may have played a part, discovering an un-torqued cam holder isn't something I expected. A leak down test indicated something was wrong with #4 but I stupidly thought it would be okay until fall I never anticipated a valve to drop into the cylinder,very hard lesson learned :oops: .

Regardless of cause a rebuild needs to be done so I might as well be positive and look at this as an opportunity, if anyone wants to share their cbx knowledge I'll take it all in. Whether it's a performance upgrade or just a reliability improvement I'll consider all suggestions. I may not be able follow all the advice I have a limited budget due to being forced into early retirement from sports/work injuries. Coincidentally the engine rebuild that'll begin this September will coincide with my first knee rebuild in October, if successful it will allow me to be working and riding again by april/march of 2018...

Here's the starting point in pictures.
7281
7277
7283
7284
7285
and the largest debris I found, clearly there are more to be found in the lower case...
7282

first replacement part a piston is on it's way, Wiseco overbore from a CB900
I've never opened the lower case on my own before, it's intimidating but to reduce costs I need do as much as I can on my own before I hand it over to a very skilled mechanic...
CBX a work in progress, still improving...GS1150EFE completed and awaiting modifications.....RD350, remnants in boxes scattered throughout the garage

User avatar
FalldownPhil
ICOA Member
ICOA Member
Posts: 929
Joined: Fri Feb 10, 2006 11:25 pm
Location: Marina Del Rey, CA. USA
Contact:

Re: 79 engine rebuild

Post by FalldownPhil »

There could be a clue in these photos. Was the shim still in the bucket of that buggered cam lobe??
Best,
Phil
When you are up to your ass in alligators it is sometimes difficult
to remember that your objective was to drain the swamp !!

User avatar
wyly
ICOA Member
ICOA Member
Posts: 1727
Joined: Tue Oct 30, 2007 4:20 pm
Location: calgary alberta canada
Location: Calgary Canada

Re: 79 engine rebuild

Post by wyly »

FalldownPhil wrote:There could be a clue in these photos. Was the shim still in the bucket of that buggered cam lobe??
Best,
Phil
nope it was on top of the head...when I changed the the shims i rotated the engine a few times by hand to make sure they were all seated...the damage on the cam lobe is reflective of that on the bucket...
CBX a work in progress, still improving...GS1150EFE completed and awaiting modifications.....RD350, remnants in boxes scattered throughout the garage

User avatar
FalldownPhil
ICOA Member
ICOA Member
Posts: 929
Joined: Fri Feb 10, 2006 11:25 pm
Location: Marina Del Rey, CA. USA
Contact:

Re: 79 engine rebuild

Post by FalldownPhil »

Me thinks that your CBX spit a shim. As the shim was coming out it pushed the valve open too far and the rest is history.
The chips on the cam are indicative of the cam running on a bucket with no shim. I think it may have been the shim
first and the rest cascaded from there. Then again :think: Truly a shame that it is so complicated (expensive) to get
a head to you.
Very Best,
Phil
When you are up to your ass in alligators it is sometimes difficult
to remember that your objective was to drain the swamp !!

daves79x
ICOA Technical Director
ICOA Technical Director
Posts: 4736
Joined: Sun Oct 01, 2006 8:05 am
Location: Knox, PA
Location: Knox, PA

Re: 79 engine rebuild

Post by daves79x »

You got it Phil - my thoughts exactly! Very, very unusual for a CBX to spit a shim. Did you use any 'cut down' shims made to fit, or were they all standard Honda? Too bad that little bugger caused all this expensive damage!

Again, let us know the parts you need as you go along.

Dave

jnnngs
ICOA Member
ICOA Member
Posts: 420
Joined: Tue Feb 10, 2015 2:05 pm
Location: Hants/UK
Location: Hants/UK

Re: 79 engine rebuild

Post by jnnngs »

Hi,

So would this explain the original symptoms?

If a shim wasn't seated properly then the valve wouldn't close properly - which is probably what was showing up in the leak down test.

Paul.

User avatar
FalldownPhil
ICOA Member
ICOA Member
Posts: 929
Joined: Fri Feb 10, 2006 11:25 pm
Location: Marina Del Rey, CA. USA
Contact:

Re: 79 engine rebuild

Post by FalldownPhil »

Paul,
In a word "YES".
Phil
When you are up to your ass in alligators it is sometimes difficult
to remember that your objective was to drain the swamp !!

Mouse
ICOA Member
ICOA Member
Posts: 569
Joined: Fri Jun 12, 2015 9:56 am
Location: Canmore Alberta Canada
Location: Canmore Alberta Canada

Re: 79 engine rebuild

Post by Mouse »

:shock:
That a piece so small as a shim could cause so much damage when it fails. :no
Canadian Amateur Radio Call sign VE6 VES

User avatar
wyly
ICOA Member
ICOA Member
Posts: 1727
Joined: Tue Oct 30, 2007 4:20 pm
Location: calgary alberta canada
Location: Calgary Canada

Re: 79 engine rebuild

Post by wyly »

I spoke with local engine specialist he doesn't think it was the shim...from my limited compression of his technical explanation his thoughts centered on the failed leak down test and where the leaky valve broke(right at the head)...something was up with that particular valve, he suspects either the valve was already bent on install or installed incorrectly(something about not being seated properly.)..he suspects the shim was snapped by the impact from below driving it into the cam lobe...
Last edited by wyly on Wed Jul 05, 2017 8:22 pm, edited 1 time in total.
CBX a work in progress, still improving...GS1150EFE completed and awaiting modifications.....RD350, remnants in boxes scattered throughout the garage

User avatar
wyly
ICOA Member
ICOA Member
Posts: 1727
Joined: Tue Oct 30, 2007 4:20 pm
Location: calgary alberta canada
Location: Calgary Canada

Re: 79 engine rebuild

Post by wyly »

daves79x wrote:You got it Phil - my thoughts exactly! Very, very unusual for a CBX to spit a shim. Did you use any 'cut down' shims made to fit, or were they all standard Honda? Too bad that little bugger caused all this expensive damage!

Again, let us know the parts you need as you go along.

Dave
standard Honda shim...leak down test was done twice on that cylinder with different shims same result both times , I made sure it was seated by rotating through the firing order, all good and tight..

I'll keep you informed on parts required...Tims has the cylinder sleeve I need and I was referred to a shop that has the technical capability to install it.
CBX a work in progress, still improving...GS1150EFE completed and awaiting modifications.....RD350, remnants in boxes scattered throughout the garage

User avatar
wyly
ICOA Member
ICOA Member
Posts: 1727
Joined: Tue Oct 30, 2007 4:20 pm
Location: calgary alberta canada
Location: Calgary Canada

Re: 79 engine rebuild

Post by wyly »

I got a recommendation for a one man shop to re-sleeve my cylinder, I called him told what happened he was curious as to the cause and asked me to bring in the broken parts for examination... verdict ...faulty valve install

he told me an engine with upper end rebuild with only 10km/6k miles shouldn't have valves in the condition that he was seeing ...there were a number of other valves not seated/concentric, it was just a matter of time until one failed...he said seating valves properly is very critical work and very few shops have the training or the quality of equipment to do it with the precision required...

I felt better hearing that it wasn't my fault but then he spoiled it by adding to growing list of parts, new cam chains even thought the old ones look fine, exhaust cam possibly cam couplers, maybe the cam guides ...and potentially more when the bottom cases are opened it's gonna be expensive, again :(

very impressive operation, I've never seen motorcycle shop that clean or well equipped, a machine shop wouldn't be better equipped, all work is done in house...
CBX a work in progress, still improving...GS1150EFE completed and awaiting modifications.....RD350, remnants in boxes scattered throughout the garage

User avatar
FalldownPhil
ICOA Member
ICOA Member
Posts: 929
Joined: Fri Feb 10, 2006 11:25 pm
Location: Marina Del Rey, CA. USA
Contact:

Re: 79 engine rebuild

Post by FalldownPhil »

Speaking from experience, it will be cheaper to take a good engine and put all
the parts in your cases if you want to preserve the VIN numbers.
Best,
Phil
When you are up to your ass in alligators it is sometimes difficult
to remember that your objective was to drain the swamp !!

User avatar
wyly
ICOA Member
ICOA Member
Posts: 1727
Joined: Tue Oct 30, 2007 4:20 pm
Location: calgary alberta canada
Location: Calgary Canada

Re: 79 engine rebuild

Post by wyly »

FalldownPhil wrote:Speaking from experience, it will be cheaper to take a good engine and put all
the parts in your cases if you want to preserve the VIN numbers.
Best,
Phil
that's a good point Phil but how will "I" know it's a good engine, I don't have the experience that you Dave or Herdy Gerdy do... I asked the the re-builder a similar question about buying a used cylinder head , "It's a gamble you won't know until I look it over " ...I've been offered two complete engines (79 and 81)but the owner admits he has no idea what condition either is in...

the guy with the CBX hoard who lives not far away called me up an hour ago, I thought maybe he'd soften on his sales tactic and was offering to break up his hoard...but no, it's still $12K for the head and he'll throw in the rest of his hoard as a bonus... refuses to sell his spares separately...

my next task is to locate/buy a clutch tool so I can progress the damage investigation into the bottom end.
CBX a work in progress, still improving...GS1150EFE completed and awaiting modifications.....RD350, remnants in boxes scattered throughout the garage

User avatar
FalldownPhil
ICOA Member
ICOA Member
Posts: 929
Joined: Fri Feb 10, 2006 11:25 pm
Location: Marina Del Rey, CA. USA
Contact:

Re: 79 engine rebuild

Post by FalldownPhil »

You will know it is a good engine after doing a couple of tests on it just like you did with your present engine.
Then it will come apart to wrap it in the old cases.
Best,
Phil
When you are up to your ass in alligators it is sometimes difficult
to remember that your objective was to drain the swamp !!

daves79x
ICOA Technical Director
ICOA Technical Director
Posts: 4736
Joined: Sun Oct 01, 2006 8:05 am
Location: Knox, PA
Location: Knox, PA

Re: 79 engine rebuild

Post by daves79x »

Wyly, also from experience, seating and lapping valves is not rocket science as your man might have implied. If each of your valves would have been simply hand-lapped, a bent valve that was not seating would have been very obvious. And a simple kerosine leak test on the finished head would have shown which valves still were not seating. Now, replacing and reaming guides is a whole other matter. Bottom line is someone didn't do a very good job of a fairly straightforward procedure.

Now if you decide that you trust this guy you found, you'll have to go the whole way with his recommendations. You are correct, it will be expensive.

Again, I'll help you with any parts I can.

Post Reply

Return to “Project Threads”