Author Topic: 750 top end oil leak (Read 3893 times)

Thousandson · « **on:** May 19, 2015, 05:40:41 PM »

Cb750f 78'

I had an oil leak last year, I knew exactly where it was. I figured it was the six rubber pucks, and the four o rings. I replaced all of those, and I still have the exact same leak.

I am looking for answers. Does the super sport engine have these problems? Is the 78'ss and the standard 78' share the same engine? Is their a common leak problem in this year?

When I first rebuilt the engine, i used a little casket crinch under the pucks to prevent leaks. This time I used some form a gasket sealant, under the pucks and still seams to be leaking. Am I missing a leak problem?

Jerry Rxman Griffin aka MuthaF'er · « **Reply #1 on:** May 19, 2015, 06:19:37 PM »

Perhaps the cam tower studs. If you took them out and didn't use a sealer/thread lock this could be your problem.

Any of 750's can do this.

flybox1 · « **Reply #2 on:** May 19, 2015, 09:18:52 PM »

The copper crush washers (under the acorn nuts) did you anneal them, or use new ones?

evanphi · « **Reply #3 on:** May 21, 2015, 07:23:03 AM »

Quote from: Jerry Rxman Griffin aka MuthaF'er on May 19, 2015, 06:19:37 PM

Perhaps the cam tower studs. If you took them out and didn't use a sealer/thread lock this could be your problem.

Any of 750's can do this.

The holes for the bolts are also blind, so they aren't SUPPOSED to go through to the underside of the head... but if they do the oil might be leaking through.

AintNoEasyWay · « **Reply #4 on:** May 21, 2015, 08:11:18 AM »

Any photos of it? Where exactly is the link? HondaMan states in the books that our 77's & 78's run hotter & are thus more prone to leaks. Jerry has a good point: did you you remove the cam tower studs? I actually just posted about this in my build thread, because this popular thread (http://forums.sohc4.net/index.php?topic=107040.0) recommends removing the cam studs & putting Loctite on them.

Also, I think the 78k's & 78f's share slightly different engine in that there are minor differences such as number of dowels between the crankcase & jugs, etc.

flybox1 · « **Reply #5 on:** May 21, 2015, 08:18:46 AM »

Quote from: AintNoEasyWay on May 21, 2015, 08:11:18 AM

Any photos of it? Where exactly is the link? HondaMan states in the books that our 77's & 78's run hotter & are thus more prone to leaks. Jerry has a good point: did you you remove the cam tower studs? I actually just posted about this in my build thread, because this popular thread (http://forums.sohc4.net/index.php?topic=107040.0) recommends removing the cam studs & putting Loctite on them.

Also, I think the 78k's & 78f's share slightly different engine in that there are minor differences such as number of dowels between the crankcase & jugs, etc.

locktite will not prevent leaks on the cam tower studs. thread sealer should be used.

AintNoEasyWay · « **Reply #6 on:** May 21, 2015, 08:24:20 AM »

Ah yea, good catch Flybox!

PeWe · « **Reply #7 on:** May 21, 2015, 11:34:34 AM »

The cam tower studs threads in head might be bad as well. Good idea to install Time-Sert inserts. Locked with Loctite 272, stud threads get Permatex teflon high temp sealer or similar. The other threads migh be bad too.
Do not tighten bolts, nuts too much, I did 10Nm (7.4 ft lb) max last time on all M6 on cam towers, caps. I have stripped threads before when tighten max. Manual seems to be too positive about the torque. Important with reliable tools tighten correct.

Thousandson · « **Reply #8 on:** May 24, 2015, 12:40:47 PM »

I will take a picture and circle exactly where it is dripping from. On top of the #3 cylinder, #2 is perfectly fine. I have to pull it, I will check with my mechanic. Thanks guys, this really sucks but thank you for getting back to me. I cant wait to get her back up and running the way she should be.

Thousandson · « **Reply #9 on:** May 24, 2015, 12:47:26 PM »

FYI, I did not take the cam tower studs out. Might be a good idea to order more, replace them, and use thread sealer.

I also used the old copper washers. I will get news ones. If its just 4 washers I can deal with that.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #10 on:** May 24, 2015, 11:30:18 PM »

Good luck finding NEW cam tower studs. Shouldn't be necessary.

PeWe · « **Reply #11 on:** May 25, 2015, 01:11:08 AM »

You can check with your finger if the studs are leaking. Remove spark plug so your finger can enter and you can feel the upper side of the head. It should be possible to check with lamp and mirror to verify its wet of oil or not.

Bailgang · « **Reply #12 on:** May 25, 2015, 06:14:01 AM »

I recently dealt with a top end leak on my 77 F2, I had rebuilt the top end last year using an aftermarket gasket set however I pitched all the o-rings that came with the kit and used viton o-rings instead. I did use the rubber pucks that came with the kit and initially the engine was leak free however late last year it started leaking so this spring I pulled the cam out to retorque the cyl head and in the process found my leak was coming from the rubber pucks but like a chump rather than replace them I just put sealant on them and bolted it all back up. The sealant didn't do squat and it leaked even worse afterwards so a few weeks ago I ordered a set of genuine Honda rubber pucks rather than aftermarket ones and this time used permatex hylomar HPF on them and as recommended above I removed the studs and reinstalled them with thread sealant. It's too early to say whether this took care of the leak on a long term basis but as it stands right now it doesn't leak anymore and what made life easier for me is that I have a frame kit from member 754 so I can pull the top end apart with the engine still in the frame.

The only thing I can add to what's already been mentioned is that while you have the cam towers out you might as well take some time to retorque the cyl head while you're at it.

Thousandson · « **Reply #13 on:** May 26, 2015, 04:05:45 PM »

I forgot to take a picture, but I found the best one I could online. The red circle shows the exact oil leak location. right next to my exhaust port.

After reading all of your replies, its looking like the pucks, or one of the cam bots. I am buying thread sealant right now.

AintNoEasyWay · « **Reply #14 on:** May 26, 2015, 06:02:54 PM »

That's exactly where my leak was. I haven't got my engine back in the frame yet, but I went ahead & did a top end rebuild, replacing most parts. Maybe someone else can chime in & confirm that it's likely to be pucks.

MCRider · « **Reply #15 on:** May 26, 2015, 06:17:30 PM »

Quote from: AintNoEasyWay on May 26, 2015, 06:02:54 PM

That's exactly where my leak was. I haven't got my engine back in the frame yet, but I went ahead & did a top end rebuild, replacing most parts. Maybe someone else can chime in & confirm that it's likely to be pucks.

If tis old, then the pucks might be hard and leaky.

The studs rarely leak unless they have been removed, disturbing the factory seal. Requiring renewed sealing.

hondaron · « **Reply #16 on:** May 26, 2015, 07:52:14 PM »

FYI I've had a similar issue years ago

My issue was caused by heli coiling stripped out threads in the head.

They were not flush with the head surface and were causing a leak under the cam towers.

So if you did any heli coil or time sert repairs you might make sure this isn't causing your issue

Restoration Fan · « **Reply #17 on:** May 27, 2015, 04:43:46 AM »

On the 77's and 78's, the F model head is slightly different from the K model head according to what Bill Benton told me. The F head has slightly larger valves and are considered the primo desired heads for the big bore guys doing the drag racing.

As far as that photo, if that's where your leak is...I'd still bet money on the leak coming from the pucks even if you replaced them. It's not hard at all for those suckers to get turned or moved if you're not super careful when you're putting the cam towers onto them and tightening them down.

MCRider · « **Reply #18 on:** May 27, 2015, 05:58:04 AM »

Quote from: Restoration Fan on May 27, 2015, 04:43:46 AM

On the 77's and 78's, the F model head is slightly different from the K model head according to what Bill Benton told me. The F head has slightly larger valves and are considered the primo desired heads for the big bore guys doing the drag racing.

As far as that photo, if that's where your leak is...I'd still bet money on the leak coming from the pucks even if you replaced them. It's not hard at all for those suckers to get turned or moved if you're not super careful when you're putting the cam towers onto them and tightening them down.

I think it was HondaMan who pointed out that some aftermarket pucks are not full thickness and will leak when new. Best to use OEM or know the thickness and measure yours before using them.

evanphi · « **Reply #19 on:** May 27, 2015, 07:53:17 AM »

Quote from: MCRider on May 27, 2015, 05:58:04 AM

Quote from: Restoration Fan on May 27, 2015, 04:43:46 AM
On the 77's and 78's, the F model head is slightly different from the K model head according to what Bill Benton told me. The F head has slightly larger valves and are considered the primo desired heads for the big bore guys doing the drag racing.

As far as that photo, if that's where your leak is...I'd still bet money on the leak coming from the pucks even if you replaced them. It's not hard at all for those suckers to get turned or moved if you're not super careful when you're putting the cam towers onto them and tightening them down.
I think it was HondaMan who pointed out that some aftermarket pucks are not full thickness and will leak when new. Best to use OEM or know the thickness and measure yours before using them.

YES. You should have 0.030" of compression. Make a shim, if necessary.

Quote from: HondaMan on September 07, 2013, 09:07:14 PM

Installed the head seals after the retorque today. Pix below: with the crop of too-thin head seals we keep seeing, here is a way you can check the ones you got in your gasket kit (or elsewhere, like PartsNmore or CB750Supply, etc.).

First, check the step depth of the head hole. Then, check the thickness of your seal. You need at LEAST .030" compression, .040" is better. The too-thin ones are only about .005" thicker, which won't seal when the head heats up and the hole becomes deeper.

Then I spread the non-hardening sealer around the edges of the seals (messy!) and twist them into their holes to seat them and their goo.

Quote from: evanphi on April 11, 2015, 03:49:11 PM

Finally got everything all buttoned up!

The blank canvas...

Permatex FormAGasket 2 goes in the recesses, then the 0.030" shims.

Then the pucks had a bit more Permatex put on their edges, and sat down into the recesses. Pressed them down as much as I could to force out any excess, then cleaned up.

flybox1 · « **Reply #20 on:** May 27, 2015, 08:37:10 AM »

Quote from: Thousandson on May 24, 2015, 12:47:26 PM

FYI, I did not take the cam tower studs out. Might be a good idea to order more, replace them, and use thread sealer.

I also used the old copper washers. I will get news ones. If its just 4 washers I can deal with that.

BINGO!

your copper washers were 'crushed' the first time by whomever assembled the head.
if you did not anneal them, or use NEW ones, they have no more pliability, will not compress, and will be a leak point.
get new ones.

AintNoEasyWay · « **Reply #21 on:** May 27, 2015, 09:08:32 AM »

Quote from: flybox1 on May 27, 2015, 08:37:10 AM

Quote from: Thousandson on May 24, 2015, 12:47:26 PM
FYI, I did not take the cam tower studs out. Might be a good idea to order more, replace them, and use thread sealer.

I also used the old copper washers. I will get news ones. If its just 4 washers I can deal with that.
BINGO!

your copper washers were 'crushed' the first time by whomever assembled the head.
if you did not anneal them, or use NEW ones, they have no more pliability, will not compress, and will be a leak point.
get new ones.

Are you guys referring to the copper washers that go around the exhaust ports?

flybox1 · « **Reply #22 on:** May 27, 2015, 09:20:18 AM »

Quote from: AintNoEasyWay on May 27, 2015, 09:08:32 AM

Quote from: flybox1 on May 27, 2015, 08:37:10 AM
Quote from: Thousandson on May 24, 2015, 12:47:26 PM
FYI, I did not take the cam tower studs out. Might be a good idea to order more, replace them, and use thread sealer.

I also used the old copper washers. I will get news ones. If its just 4 washers I can deal with that.
BINGO!

your copper washers were 'crushed' the first time by whomever assembled the head.
if you did not anneal them, or use NEW ones, they have no more pliability, will not compress, and will be a leak point.
get new ones.

Are you guys referring to the copper washers that go around the exhaust ports?

No.....i am referring to the 4 copper crush washers in the head, under the acorn nuts.

HONDA brand crush washers are $2 or more EACH

I found a 10pk of 5/16"X11/16" SAE Copper Sealing Washer (1/16" thick) for $.70

locally.
They worked perfectly.

Elan · « **Reply #23 on:** May 27, 2015, 10:15:53 AM »

Just to add for reference to anyone else with a leak like this... I had the same leak after a rebuild and discovered I had an f head on a k engine. The oil passages are different and oil was spilling out of that exact spot.

AintNoEasyWay · « **Reply #24 on:** May 27, 2015, 10:45:42 AM »

Are you guys referring to #14 in this diagram?: http://www.hondachopper.com/engine/fiche_pages/K7/K7-Head.pdf

Never realized these were potential problems.

News:

Author Topic: 750 top end oil leak (Read 3893 times)