Author Topic: Leaky CB750K4 after 836 rebuild (Read 7303 times)

andy750 · « **on:** July 17, 2018, 03:27:37 AM »

This engine has been rebuilt more than once. This time an 836cc kit was installed and I have about 500 miles on the engine, However I have noticed oil pressure (as measured by Joker Machine gauge is sometimes low: 30 psi at 65 mph and other times its fine 60 psi @ 65 mph. This past weekend I was riding to VT when I noticed all the oil on the cylinder fins - both sides - however it was on the lower fins as well and coating the airbox. Not obvious to me where its coming from as front of engine appears dry. Any suggestions on where to look? I realise pucks are the obvious answer but since front is dry....

thanks for any suggestions. Very disappointed at this point.
cheers
Andy

calj737 · « **Reply #1 on:** July 17, 2018, 05:16:19 AM »

First, clean and degrease the engine. Then, gently spread some talcum powder along the suspected surfaces. When oil leaks it will be immediately noticeable.

Second, when you rebuilt the motor, did you re-torque the studs after 24hr or any heat cycles? And, was the head and deck milled flat and true?

I’d focus on a re-torque personally. Release all the studs in reverse order, then step the studs back in to their spec with 2 stages, not a single full pass. This insures a nice even squish and a quality torque spec.

andy750 · « **Reply #2 on:** July 19, 2018, 11:03:07 AM »

Thanks Cal for the reply. I am going to have Mike take a look at it and see if its as simple as a re-torque.

PeWe · « **Reply #3 on:** July 19, 2018, 02:23:42 PM »

Except leaking head gasket..
Any oil inside the spark plug cavities?
Feel with finger when engine is cold, rubber pucks or cam studs leaking visible here, from the ceiling.

Or an o-ring that jumped out of its position when mounting the head.
Or too long knock pins that hit head-cyl before gasket is fully compressed.

andy750 · « **Reply #4 on:** July 19, 2018, 06:16:58 PM »

Ah good idea PeWe on the spark plug cavities Ill take a look this weekend.

PeWe · « **Reply #5 on:** July 20, 2018, 10:44:34 AM »

I fully understand the feeling. Work hard, spend money and it will leak oil. I'm sure that all of us CB guys have been there or are there.
Feel the smell of warm oil after a ride on a fresh restored bike can cause allergy. Motul oils smells extra much, not raspberry as the old Vance & Hines oil.

Mooshie · « **Reply #6 on:** July 20, 2018, 12:23:26 PM »

Quote from: PeWe on July 20, 2018, 10:44:34 AM

I fully understand the feeling. Work hard, spend money and it will leak oil. I'm sure that all of us CB guys have been there or are there.
Feel the smell of warm oil after a ride on a fresh restored bike can cause allergy. Motul oils smells extra much, not raspberry as the old Vance & Hines oil.

CB girls have the same dilemma

. Andy I feel your pain. I did the top end and it is a work of art however the darned thing is leaking from the head gasket. The good part is that my spark plug cavities are clean as a whistle now. My solution? Sending it to Hondaman next week--I figure if anyone can sort out my sweet Dash it is Mark

Good luck. I think once your oil leak is solved we should go on a ride!

andy750 · « **Reply #7 on:** July 20, 2018, 05:37:03 PM »

Oh I have been in leaky engine hell before with the K2

And Mike R was the engine builder

But he eventually figured it out after the third time of pulling the engine and lots of time...hair thin crack in head caused it to leak - super rare event. Mikes patience paid off as the K2 is now a dream to ride and it puts a smile on my face every time. When MikeR heard the K4 was leaking he immediately offered to help - i am super lucky to know Mike!! Very lucky!

So in time I know it will get fixed but I was hoping for some super long rides this summer and so far its not happened - my VStrom DL1000 is out with a friend stator that is in now in bits waiting for the part. The K2 is going to get put into service instead

Cant wait to ride with you Mooshie! Someday! We can invite PeWe over and Ill give him the K4

Stay tuned for updates...
cheers
Andy

PeWe · « **Reply #8 on:** July 22, 2018, 12:30:09 AM »

I heard about an old CB750 K0 in really good shape (like new) except for an oil leak. After some replacements of head gasket the problem was found, a really fine crack in the cylinder block.

andy750 · « **Reply #9 on:** July 22, 2018, 06:25:10 PM »

I dont know how it happens but thats what I had in my K2 head....fine crack...leaked every time after ~10 miles. It came from a "free" engine.

andy750 · « **Reply #10 on:** August 24, 2018, 03:32:49 PM »

Ok its been a while but progress has been made on the leaky 836cc engine....here is a reminder of the problem...rebuilt lower end due to 4th gear skipping...decided at same time to fit a 836cc kit (cruizimage)....after ~500 miles...oil leaking profusely across engine fins and secondary leaks out of the bottom of the engine.

andy750 · « **Reply #11 on:** August 24, 2018, 03:35:46 PM »

The solution...MikeR offered to look at it for me...thank you Mike!!! Even though MikeR was not the engine builder he stepped in when issues arose and saved this bike..... And so began my top end engine class education....

First - lucky I had a frame kit! After years of removing engines from both my K2 and K4 I fitted a frame kit to both bikes for moments like this...on MikesR lift ready for diagnosis...

andy750 · « **Reply #12 on:** August 24, 2018, 03:42:53 PM »

MikeR is an excellent teacher and his knowledge of engines (any bike) is just amazing! The stud nuts were not very tight when we came to remove them....and the head gasket (Vesrah) was leaking oil all over the place...NEVER use VESRAH head gasket!!!!!!

andy750 · « **Reply #13 on:** August 24, 2018, 03:45:14 PM »

Engine waiting for a new triple layer gasket.....the paste on the gasket is Hondabond

andy750 · « **Reply #14 on:** August 24, 2018, 03:47:09 PM »

Mike sanded down the head before installation...and check out those OEM clamps - the only ones to use!!!

andy750 · « **Reply #15 on:** August 24, 2018, 03:49:19 PM »

The gear shift cover was leaking so that came off and since I had to replace the starter motor (coincedence) the alt cover came off as well revealing Anders alt upgrade....great for easy starting and running heated gear

andy750 · « **Reply #16 on:** August 24, 2018, 03:54:26 PM »

Head back on...all torqued down....3 times going through the sequence....leave overnight and check the next day...MikeRs attention to detail is just amazing...all the while he is working on the Sorcerer engines....which look absolutely amazing!

calj737 · « **Reply #17 on:** August 24, 2018, 04:09:42 PM »

Quote from: andy750 on August 24, 2018, 03:42:53 PM

The stud nuts were not very tight when we came to remove them....

Called that one straight out of the gate

As much of a hassle as it is to pull down a motor, a simple “maintenance fix” is a great relief. And having the chance to learn anything under Mikes tutelage is a major boon. Heck, I might just tear up a motor to have him tear it down

andy750 · « **Reply #18 on:** August 24, 2018, 04:19:46 PM »

Yes you did Cal and I was very surprised as engine builder is a very good mechanic/machinist.

I am very much relieved to be in the MikeR garage and to be learning. There is no hurry on this K4 rebuild as the K2 (810cc) MikeR did for me years ago satisfies the CB750 needs...every time I ride it I get a smile on my face.

calj737 · « **Reply #19 on:** August 24, 2018, 04:45:20 PM »

Quote from: andy750 on August 24, 2018, 04:19:46 PM

I was very surprised as engine builder is a very good mechanic/machinist.

I wouldn't blame the builder for a second about the head nuts coming loose. Thats more a function of the gasket compressing overnight than builder "quality". He may have said something to you, that you missed, or may not have said anything assuming you knew better.

It doesn't matter in the end, as its settled now and the original builder and your new one are both responsible for putting those "miles of smiles" on your face

andy750 · « **Reply #20 on:** August 24, 2018, 05:23:01 PM »

Totally agree Cal and well said. All that matters at this point is getting my 87,000 mile CB750K4 back on the road. For the last 50,000 miles with me it has been a great ride and I look forward to at least 50,000 miles more! With MikeR at the helm I am sure this is possible!

cheers
Andy

MRieck · « **Reply #21 on:** September 13, 2018, 10:23:37 AM »

Quote from: calj737 on August 24, 2018, 04:45:20 PM

Quote from: andy750 on August 24, 2018, 04:19:46 PM
I was very surprised as engine builder is a very good mechanic/machinist.
I wouldn't blame the builder for a second about the head nuts coming loose. Thats more a function of the gasket compressing overnight than builder "quality". He may have said something to you, that you missed, or may not have said anything assuming you knew better.

It doesn't matter in the end, as its settled now and the original builder and your new one are both responsible for putting those "miles of smiles" on your face

I agree Cal. Andy was over last night and we are going over the bike attacking potential problems too. It is working out well. I'll let Andy give the details.

andy750 · « **Reply #22 on:** September 14, 2018, 05:59:29 PM »

This past Wednesday we made some great progress...and as always you find more issues the more you look...oil lines were kinked which may have contributed to low oil pressure...lucky I had some new ones ordered a while back from forum member Edwardmorris (of K2 rebuild fame). Here they are installed

It was a tight fit

And new overflow hoses as old ones rock hard after 87,000 miles

Sent from my iPhone using Tapatalk

andy750 · « **Reply #23 on:** September 14, 2018, 06:03:51 PM »

There had been a lot of oil coming out right side of engine underneath and so taking no chances replaced oil pan gasket with a no-leak Cycle-X one - these gaskets look great and MikeR recommends them so...drop the oil pan

New Cycle-X gasket perfect fit

And all buttoned up.

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andy750 · « **Reply #24 on:** September 14, 2018, 06:07:54 PM »

New Webcam and sprocket!!

New pucks of course

Cam towers installed

The patient is ready...

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Author Topic: Leaky CB750K4 after 836 rebuild (Read 7303 times)