Author Topic: very bad day (Read 3044 times)

KRONUS0100 · « **on:** April 18, 2010, 04:44:08 PM »

just got home and in from barn. Decided to take my 76 CB750 F for a decent maiden voyage since the motor rebuild. She came home on a trailer after 83 miles. Good news...Rings are broken in and properly seated. Bad news.............upper end failure..either cam is broke in 1/2 or the brand spankin new Tsubaki cam chain is broken. I pulled the tensioner and its working properly....chain is still wrapped around crank and cam...tried to pull it thru tensioner hole....it wont move but a fraction of an inch. Motor spins and cam dont move at all. Finish pulling it tommorrow and try and get pics up on imageshack. VERY BAD DAY.....and naturally of all the bikes I have done motor work on...ITS MY BIKE THAT BREAKS!!!!! WAAAAAAAAHHHHHHHHHHHHHHHHHH!!!!!

HondaMan · « **Reply #1 on:** April 18, 2010, 04:50:43 PM »

Uh, oh. I hope you didn't forget the 4 tiny O-rings under the cam towers that seal the oil passages....

MCRider · « **Reply #2 on:** April 18, 2010, 05:06:29 PM »

Neither side of the cam turns? Like 1-2 but not 3-4, or vice verasa?

I've never seen a cam seize both sides and break out the sprocket in the middle. Let us know what happened.

KRONUS0100 · « **Reply #3 on:** April 18, 2010, 05:12:06 PM »

no..I didnt forget those tiny little o rings.............its possible that the sprocket bolts sheared off...but i dont have a clue as to why..............I even put a dab of blue loctite on them because I have had them back out before.........seems funny though...the motor just quit like it was shut off...no loss of power...no major noise or locking up the drivetrain....very wierd. Like I said..motor will be on workbench tommorrow afternoon and i will get pictures posted to image shack.

MCRider · « **Reply #4 on:** April 18, 2010, 05:18:34 PM »

The problem of lack of oil pressure to the cam towers is most likely clogged passageways and not the lack of ORings. Been there.

At first i thought you may have broken the cam in two places leaving the center free to spin, assunimg it still had some contact in the bearing journals.

But your statement of broken sprocket bolts makes more sense. The cam could have seized both sides and rather than break the shaft, it broke the sprocket bolts. Gotta admit though, those things are pretty tough buggers. But nothings tougher than a seized bearing.

Anyway we know something broke. I feel your pain. Good luck.

Hush · « **Reply #5 on:** April 18, 2010, 05:28:32 PM »

Like McRider said...we feel your pain mate.

sparty · « **Reply #6 on:** April 18, 2010, 05:58:17 PM »

I am gonna follow this thread.

Sparty

KRONUS0100 · « **Reply #7 on:** April 19, 2010, 07:35:49 AM »

ok folks...final tally of damage....4 bent valves from minimal contact to tops of 3 and 4 pistons.....1 head gasket......valve cover gasket.......cam gear is trashed...may have to replace the cam if i cant run a tap thru the holes.......Tsubaki cam chain is in 1 piece and no damage visible. It would appear that the bolts for the cam gear backed out...even with the locktite applied. So...to the p[arts motor I go...just hope I got a decent spare cam...anyone know what a cam from ape or dynoman runs?

thanks. Matt

KRONUS0100 · « **Reply #8 on:** April 19, 2010, 07:36:26 AM »

oops...forgot...uploading pics to imageshack here in a few moments.

KRONUS0100 · « **Reply #9 on:** April 19, 2010, 08:06:44 AM »

oops again..pics are at image shack...under name of mbrizfam590......not sure how to get them here though....having a wee bit of trouble with that concept

KRONUS0100 · « **Reply #10 on:** April 19, 2010, 08:09:47 AM »

[img=http://img404.imageshack.us/img404/4826/betterviewofbolts.th.jpg]
[img=http://img263.imageshack.us/img263/6493/uhohcontactwithvalveson.th.jpg]
[img=http://img263.imageshack.us/img263/9513/viewofvalveson3and4uhoh.th.jpg]
[img=http://img145.imageshack.us/img145/6084/valvecoveroffcamgearbol.th.jpg]
[img=http://img228.imageshack.us/img228/2153/insidevalvecoverdamager.th.jpg]
[img=http://img263.imageshack.us/img263/6905/myblue1976hondacb750f.th.jpg]

MCRider · « **Reply #11 on:** April 19, 2010, 08:11:37 AM »

Sorry about that. Sprocket bolts backing out kinda weird but stranger things have happened.

Gonzowerke · « **Reply #12 on:** April 19, 2010, 08:47:41 AM »

I was told back in the day by an old Honda Mechanic at Pete's Cycle in Md., that a good habit to get into was to peen the tip of the bolt against the cam flange with a center punch. Like you do on the wheels for the bearing retainers, where you hit the seam to deform the metal and lock the two together to prevent rotation. Whether or not this is true, I don't know. I have never done it, but then I have only ever done 2 rebuilds.

Hannibal Smith · « **Reply #13 on:** April 19, 2010, 10:42:54 AM »

Sorry to hear that!

I guess now it is only a quessing game. I have a paint marker, and put a mark on every bolt that just got torqued. All those cats have to do is become a teensy weensy bit loose, and it's curtains. Properly torqued, and if the fastener itself checks out they should not come loose.

If memory serves me right, you have the 2 cam sprocket fasteners and the starter gear shaft retainer 6mm fastener that can come loose and grenade the mill once she is buttoned up. I used a serrated belleville washer beneath my starter gear shaft fastener and loctited that mother.

I will be buttoning up my top-end pretty soon and will be on those cam sprocket fasteners like a hawk.......................thanks for the reminder, even though it came at your expense, truly sorry!

Old75_ratafe · « **Reply #14 on:** April 23, 2010, 12:49:45 AM »

::looks at pics.. cringes::

dave500 · « **Reply #15 on:** April 23, 2010, 01:06:15 AM »

i had the same on an xr 600,,im sure i tightened those bolts??rattle rattle stop,bent valves and snapped chain!ive built plenty of motors,ford windsor v8s,holden sixes and v8s,two stroke dirt bikes,,,i double check as i go twice.even the big aircraft factories have failures.

faux fiddy · « **Reply #16 on:** April 23, 2010, 01:18:35 AM »

Quote from: KRONUS0100 on April 19, 2010, 07:35:49 AM

ok folks...final tally of damage....4 bent valves from minimal contact to tops of 3 and 4 pistons.....

thanks. Matt

Bent valves? Bend them back. What I know, it's done on a bridgeport. Some say it can't be done, but it can. I will ask for a better description of what he did. It goes something like this:

Put it in a v-block, clamp it in and tink on it with a hammer. Use the milling machine to measure it precisely. Tink it back into shape. Roll it around and measure. Partner did it with a couple timing belt catastrophy cars.

I've installed them in the cars we worked on and they caused no problem,ran normal,lapped in, seated fine, good compression.

I'll ask for details, and post more.

dave500 · « **Reply #17 on:** April 23, 2010, 03:20:04 AM »

yeah boi,,that can be done,,we call it bush mechanics here in australia,and weve all fixed stuff with wire etc,the head gasket on my 500 has been used three times and still going,pistons can also be turned out of redgum(a local hardwood,very hard)these motors turn a lot faster than car ones,and once bent and straightend the strength of the stem is less than what it was,a car you might get away with,,but as you hit 9000rpm,itll be in the back of your mind if this valve is going to drop,replace any bent valves.,check the holes in that cam sprocket havent elongated,and all the bolts bits add up to a complete bolt,change the oil and filter and try again.

KRONUS0100 · « **Reply #18 on:** April 23, 2010, 05:50:46 AM »

got new used cam sprocket and bolts out of parts motor. gonna use red loctite this time..not blu...making sure i shake the piss out of the bottle beofre i use it. Cam chain is fine..already had it looked at. parts motor also yielding the 4 valves when i get that far. waiting on the new head gasket as we speak. the other new one i had just installed separated on dissassembly.

HondaMan · « **Reply #19 on:** April 23, 2010, 05:58:49 PM »

Quote from: KRONUS0100 on April 23, 2010, 05:50:46 AM

got new used cam sprocket and bolts out of parts motor. gonna use red loctite this time..not blu...making sure i shake the piss out of the bottle beofre i use it. Cam chain is fine..already had it looked at. parts motor also yielding the 4 valves when i get that far. waiting on the new head gasket as we speak. the other new one i had just installed separated on dissassembly.

Matt:
Torque those 6mm fine-thread bolts to 100 in-lbs.

News:

Author Topic: very bad day (Read 3044 times)