Author Topic: Stev-o's K4 "Big Bang Theory"!  (Read 34361 times)

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Offline Stev-o

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Stev-o's K4 "Big Bang Theory"!
« on: April 29, 2017, 07:16:25 AM »
Looks like I'm going to be building a motor for my K4. A little back story:

Took the day off work yesterday, was to be a great day to ride the Texas Hill Country.  Rolled the K4 out of the garage, did the usual checks, aired the tires up, oil level was fine, tightened a loose turn signal on the R rear.

I had charged the battery the night before in preparation and the bike started right up and sounded fine, just as always since I've owned it 5+ years....


 


So I gear up and take off, heading west around 10:30am with Llano TX as my lunch destination, about 70 miles of scenic twisty roads in the Hill Country.

I'm on Ranch Road 1431 traveling around 65 [speed limit 55] and am approaching a car in front traveling slower. There are only a few safe places to pass on this road and one is coming up, the Cow Creek Road bridge.
So I down shift into 3rd and accelerate full throttle, pass the car and am doing no more than 90 and all of a sudden I hear a knocking sound and the oil light comes on...WTF?!!  I've done this a thousand times with this bike, it always ran great, not a single issue since I've owned it.

There is a narrow shoulder on the road at this area so I pull over to a safe place asap, the motor is still running but sounds horrible, a puff of smoke leaves the motor area when I shut it down.  Park the bike and look over the motor, could not believe it, there is a frickin hole in the case!!
I call my riding buddy [who should have been with me] he's at least an hour away but is busy on a work project. He suggests calling another buddy, but I didnt want to wait, so I get stuck out my thumb to get a ride the 7 miles I have just traveled.

There are quite a few cars on this road, I was hopeful a friendly rancher would stop and help the stranded biker. It wasn't 5 minutes and a guy in a Mercedes AMG stopped to pick me up!  Super friendly guy, said he had a Matchbox CB750 when he was a kid and it was his favorite.
The car was Awesome!!!!


  steve meriggi


He drops me off at the intersection near my home, I didnt want him to go out of his way, I walk home get my truck and retrieve the K4. The motor started right up which makes it easy to load by myself.




steve meriggi



Get the bike home and immediately start pulling parts off so I can get a better look at it. There is a HUGE frikken hole in my case!! EDIT: turns out the rod bolt nuts vibrated loose.  WTF?!


 


 



I'll be pulling the motor in the next week or so, so this is how she sits now...








Not wanting the day to be a total loss, I jump on my trusty GPz550 for a spirited ride followed by a pitcher of stiff Margaritas!!!





I'm really not depressed or anything, I have a spare motor or two, so no biggie.
This was a great running, reliable 836 and I just want the same. I'm hoping to salvage and reuse the head, cam and pistons.
« Last Edit: October 18, 2022, 12:03:28 PM by Stev-o »
'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline calj737

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #1 on: April 29, 2017, 07:27:04 AM »
Sorry for your luck, Stev-o  :'( Although, there is a shiny side; when stuff lets go internally at speed, there is always a chance of getting thrown off as the motor locks up. So it appears the Saints above had their eye on you.  :)

Will this be the Steve Austin Rebuild? The bionic K4, better, stronger, faster than before!  :D
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Offline riverfever

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #2 on: April 29, 2017, 07:27:22 AM »
Really sorry to hear about the motor Steve. Glad you were able to get it pulled over and stopped without getting hurt.
http://forums.sohc4.net/index.php?topic=127186.0

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Offline joeyvans

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #3 on: April 29, 2017, 07:37:07 AM »
The 'ol "rapid disassembly without the aid of hand tools" trick. Really sucks, man.


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Offline evinrude7

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #4 on: April 29, 2017, 07:48:10 AM »
nice tile work.  i put that same stuff on a fireplace last year.  forgiving tile.  easy to install. 
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Offline flatlander

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #5 on: April 29, 2017, 09:22:03 AM »
ouch. glad it's only the motor that got hurt.
never a better time for margaritas. i will empty a glass to your luck!

Offline Davez134

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #6 on: April 29, 2017, 09:31:02 AM »
Damn, sorry to hear that. I'm sure you'll have it back up in no time. At least nobody tried to steal it while parked on the side of the road! ;) ;D

Offline goldarrow

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #7 on: April 29, 2017, 09:41:52 AM »
Sad to see the hole in the case, but now good opportunity to turn in into 1150cc!
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Offline Stev-o

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #8 on: April 29, 2017, 10:22:03 AM »
Thanks guys, yes it will be better, stronger, faster than before!
'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline BomberMann650

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #9 on: April 29, 2017, 10:55:42 AM »
Damn garage gnomes!  You have a cat don't ya Stev-o?

Offline ekpent

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #10 on: April 29, 2017, 11:12:21 AM »
Little dab of JB and it should polish right out !!  :)   Sorry Steve couldn't resist. Sounds like a hell of a day but glad to see you got right back up on another horse !  Hopefully that whole top end should slide right over to another block, been there done that before  ;)
« Last Edit: April 29, 2017, 11:14:15 AM by ekpent »

Offline Stev-o

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #11 on: April 29, 2017, 11:40:37 AM »
Damn garage gnomes!  You have a cat don't ya Stev-o?

Yes, the wife has two, keeps the mice at bay!

Hopefully that whole top end should slide right over to another block, been there done that before  ;)

The cylinders have always had a couple of damaged fins, although minor,  I prolly will just have my spare jugs bored out by my friendly local machinist. 
I do plan to use the head, maybe a little porting too?  Very curious to see what cam and pistons were put in there by the PO.  He was supposedly a Honda bike tech...
'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline seanbarney41

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #12 on: April 29, 2017, 01:36:26 PM »
Wow, pretty spectacular carnage!   Makes me think twice about all the big bore with stock bottom end engines I had planned.  Please keep us updated on any autopsy discoveries.  I know you know that the ride is worth the risk and worth fixin' 'em when they break so you can risk breakin' 'em again.
« Last Edit: April 29, 2017, 01:48:01 PM by seanbarney41 »
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Offline palepainter

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #13 on: April 29, 2017, 01:41:23 PM »
Damn, sorry to hear about the breakdown.  At least you were able to handled the bike as it traveled over it's own oil slick.  :)

Offline PeWe

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #14 on: April 29, 2017, 01:46:34 PM »
It will be interesting to see more of the carnage.
Rod did not jump out and piston in pieces?
 "Only" rod cap that fell off and squeezed between crank and cases which broke by the pressure?
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Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
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http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
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Offline Terry in Australia

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #15 on: April 29, 2017, 05:40:46 PM »
That is one big hole. I wouldn't think that something the PO did 5 years ago would have caused that though, especially since you've said that you've ridden it a lot Steve? Might have just been bad luck. Cheers, Terry. ;D
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Offline ChromeDreams

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #16 on: April 29, 2017, 07:12:06 PM »
bummer but sounds like you're taking it all in stride, I'm working my way through some margs right now...

Curious who you use for machining/boring services in the area, I was planning on sending out to Ape when the time comes but would love to keep it local-ish if possible.

Offline CycleRanger

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #17 on: April 29, 2017, 08:28:42 PM »
Bummmer!  :o :o >:( :( :P

You might be able to figure out why it failed after you get it apart.
« Last Edit: April 29, 2017, 08:30:35 PM by CycleRanger »
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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #18 on: April 29, 2017, 11:57:40 PM »
Huge bummer. I guess you'll find out soon what was the culprit.
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Offline PeWe

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #19 on: April 30, 2017, 12:29:24 AM »
F2 bolts and nuts are often recommended to avoid a hole like this. Std K bolts used here?
Maybe time to contact Jay at APE, He mentioned new rod coming this summer.
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline ekpent

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #20 on: April 30, 2017, 04:59:25 AM »
 Be interesting to see if the valves and the piston crown got mashed. Were those Wiseco or high compression pistons or the Cruze kit ?

Offline Stev-o

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #21 on: April 30, 2017, 06:56:17 AM »
Be interesting to see if the valves and the piston crown got mashed. Were those Wiseco or high compression pistons or the Cruze kit ?

Yeah, I'm very curious to see the extent of the damage too. Again, it was still running after it blew the hole in the case!
 My guess is they are Wiseco pistons, if it was bored out out at all.  (Can you ever believe a PO?)
It was a great runner and has pulled away from a stock 750....
'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline seanbarney41

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #22 on: April 30, 2017, 07:12:44 AM »
Be interesting to see if the valves and the piston crown got mashed. Were those Wiseco or high compression pistons or the Cruze kit ?

Yeah, I'm very curious to see the extent of the damage too. Again, it was still running after it blew the hole in the case!
 My guess is they are Wiseco pistons, if it was bored out out at all.  (Can you ever believe a PO?)
It was a great runner and has pulled away from a stock 750....
just an interesting and not necessarily related fyi...my vf500 still started and ran too after dropping an exhaust valve and totally obliterating the piston to the point that all that was left of it was the pin boss
If it works good, it looks good...

Offline ekpent

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #23 on: April 30, 2017, 08:47:38 AM »
Be interesting to see if the valves and the piston crown got mashed. Were those Wiseco or high compression pistons or the Cruze kit ?

Yeah, I'm very curious to see the extent of the damage too. Again, it was still running after it blew the hole in the case!
 My guess is they are Wiseco pistons, if it was bored out out at all.  (Can you ever believe a PO?)
It was a great runner and has pulled away from a stock 750....
just an interesting and not necessarily related fyi...my vf500 still started and ran too after dropping an exhaust valve and totally obliterating the piston to the point that all that was left of it was the pin boss
At least you both can say you  owned a running Honda Triple for just a little bit, very rare bikes !!  ;D

Offline Joseph Mills

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Re: Stev-o's K4 "Big Bang Theory"!
« Reply #24 on: April 30, 2017, 11:57:48 AM »
Sorry to hear about your catastrophic engine failure! But as others have said, it's fortunate you came out unscathed.
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