Topic: sad first start after rebuild...WHats this new leak?

[MCRider]

the timeserts were used for the 4 cam tower bolts...

Wow, you're not following my expecations. Yes, each bearing has a stud in front and a bolt in back. If your studs have never been out, that really reduces the suspicion that's where the oil is coming from.

So I'll have to say I have no recommendation.

[Elan]

hehehe we had a good run there

[MCRider]

hehehe we had a good run there

It could still be those studs. Its just a lot less likely, seems to me.

Good luck. Good thing is, its not rocket surgery, only so many things it can be, process of elimination.

[Kevin D]

Just a shot here Elan: under the cam bearings, there are supposed to be some tiny orings, four total, two at the rear of each bearing. The inside pair sit on the oil jets, and the outside pair sit at whats supposed to be a blocked off/dead end passage. Do ya have 'em all?

It's item 16 in this fiche, 4 required but only two pictured:

http://www.babbittsonline.com/honda-motorcycle-parts#/Honda/CB750K2_A__MOTORCYCLE%2c_JPN%2c_VIN%23_CB750-2000001/CYLINDER_HEAD_%2b_INSULATOR/CB750K2-JPN-A/2Y143410E14341004B

[MCRider]

Just a shot here Elan: under the cam bearings, there are supposed to be some tiny orings, four total, two at the rear of each bearing. The inside pair sit on the oil jets, and the outside pair sit at whats supposed to be a blocked off/dead end passage. Do ya have 'em all?

It's item 16 in this fiche, 4 required but only two pictured:

http://www.babbittsonline.com/honda-motorcycle-parts#/Honda/CB750K2_A__MOTORCYCLE%2c_JPN%2c_VIN%23_CB750-2000001/CYLINDER_HEAD_%2b_INSULATOR/CB750K2-JPN-A/2Y143410E14341004B

Gotta ask the question. But analytically, those hold the pressure side of the system. Them not being there would cause a loss of pressure to the cam bearings causing a seizing of the cam in the bearings. But no leak.

Edit: Not being there could also cause the oil to force feed under the cam bearings and out the rubber biscuits. So maybe you've got something.

[Ernest T]

What are the "pucks"?

[crazypj]

I would check engine breather, if it's trapped anywhere the crankcases pressurise and oil blows out of easiest place (usually seals, but you may have gotten 'lucky'  )

[MCRider]

What are the "pucks"?

There are 6 round rubber pucks, biscuits, seals whatever, about the size of a quarter, 3 under each cam bearing, which seal access holes cut in the top of the head.

[Elan]

Just a shot here Elan: under the cam bearings, there are supposed to be some tiny orings, four total, two at the rear of each bearing. The inside pair sit on the oil jets, and the outside pair sit at whats supposed to be a blocked off/dead end passage. Do ya have 'em all?

It's item 16 in this fiche, 4 required but only two pictured:

http://www.babbittsonline.com/honda-motorcycle-parts#/Honda/CB750K2_A__MOTORCYCLE%2c_JPN%2c_VIN%23_CB750-2000001/CYLINDER_HEAD_%2b_INSULATOR/CB750K2-JPN-A/2Y143410E14341004B

I have just 2, the ones on the oil jets. I'll definately make sure i put 2 more in, but I still dont think thats the problem.... the 2 that i was missing dont appear to "seal" anything..

[Elan]

I would check engine breather, if it's trapped anywhere the crankcases pressurise and oil blows out of easiest place (usually seals, but you may have gotten 'lucky'  )

Interesting.. I have a hose connected from the back of the crankcase to the bottom nipple on the oil tank, and a hose from the valve cover to the nipple on the top of the oil tank. Is that correct?

[Elan]

SO i have the cam towers out. Is it possible oil could be travelling UP with the stud pointed out below??


WIth the engine closed up, this stud is still "exposed". Here is a view looking infront of the engine, between the exhaust ports....


ANd here is looking at the stud from through the "puck hole". Notice the large GAP between the stud and the hole the stud travels through.

My question..
When the engine was running,  it looked like oil was coming up from this gap between the stud and the head. It was bubbling. But, it could have just been pouring downward into it and bubbles coming up, not sure.  IS it possible oil could be coming up from it? like if I forgot an o ring somewhere below the cylinders??

What ive ruled out so far...

--The pucks looked good, I pulled them out, and the backs were totally dry. they were sealed with gasket sealant.

---I'm fairly confident it is not the cam bearing studs, as I never touched them and they are in a different spot than where the leak seems to be coming from. ANd I think the flow was just too fast to be leaking through threads.

--- cam tower bolts. I put time serts in them, and sealant on the bolts. The oil seems to be coming out too fast for it to be these.

[Elan]

one more thing, in the video, when I turn off the engine, you can actually hear the oil bubbling out

[HondaMan]

I might try some 'generic' questions, here, as MC has covered most of the common ones already:
1. Do you have the copper sealing washers under EVERY head nut? I can't tell from the pictures. These washers deform to seal closed the holes.
2. There's an awful lot of oil in those hollow square recesses under the cam towers. That's probably coming from not having the second O-ring in place for each tower, which will pressure-feed oil under the tower (MC pointed this out earlier, I think). Good thing the engine leaked, or you would now have junk bearings and cam...
3. The HD studs question: if using the flat-topped 836cc pistons, the compression rise is only about 9.5:1 and the stock studs are usually OK if no leaks appear at the cylinder base gasket from the stretch upward of the larger torque. however, if the pistons are Wiseco with their [advertised] 10.5:1 compression (closer to 11:1 unless the head chambers are modified) then the HD studs are the best way to keep leaks from happening at the head gasket and base gasket, both. The Wiseco pistons require more torque on the head nuts, hence the need for the HD studs.

You mentioned Keenserts in the cam hold-down bolts: if these are through the head, they will leak (like MC pointed out), as the Keenserts cutting threads are serrated. In this case, the missing O-ring is also pressurizing the casting hollows under the towers, making this even worse.  I've stopped some (non-pressurized) leaks like these with JB Weld over the open end(s) of the thread hole(s), and some of them have lasted many years.

[Elan]

I might try some 'generic' questions, here, as MC has covered most of the common ones already:

1. Do you have the copper sealing washers under EVERY head nut? I can't tell from the pictures. These washers deform to seal closed the holes.
I do have washers under every bolt, but they dont look copper to me. THere was headwork done before me, maybe there was a switchout?

2. There's an awful lot of oil in those hollow square recesses under the cam towers. That's probably coming from not having the second O-ring in place for each tower, which will pressure-feed oil under the tower (MC pointed this out earlier, I think). Good thing the engine leaked, or you would now have junk bearings and cam...

The square recesses were definately full of oil. When I lifted the cam tower, a flow of oil exited.  I now understand the o-ring function a little better.

3. The HD studs question: if using the flat-topped 836cc pistons, the compression rise is only about 9.5:1 and the stock studs are usually OK if no leaks appear at the cylinder base gasket from the stretch upward of the larger torque. however, if the pistons are Wiseco with their [advertised] 10.5:1 compression (closer to 11:1 unless the head chambers are modified) then the HD studs are the best way to keep leaks from happening at the head gasket and base gasket, both. The Wiseco pistons require more torque on the head nuts, hence the need for the HD studs.

Yes, they are flat topped pistons, and there doesnt appear to be any leaking from the base or head gasket.

You mentioned Keenserts in the cam hold-down bolts: if these are through the head, they will leak (like MC pointed out), as the Keenserts cutting threads are serrated. In this case, the missing O-ring is also pressurizing the casting hollows under the towers, making this even worse.  I've stopped some (non-pressurized) leaks like these with JB Weld over the open end(s) of the thread hole(s), and some of them have lasted many years.

I used time-serts, which I guess are generally the same thing..



SO, The Idea now is that the lack of o-rings caused enough pressure under the cam towers to push oil through the time-sert threaded tower bolts? And also the washers need to be replaced with copper ones?

Seems plausible, just hard to believe that could cause the oil could come out so fast...

Should I ebay a new head?

[Elan]

geez I think I might have a F head! the top fin has 410 stamped on it... but I guess that wouldnt matter too much..

[Jerry Rxman Griffin aka MuthaF'er]

You don't have a "F" head, you have a F2/F3 head. Remember, F's were made from 1/75 until the end of the 1978 production run and the 75/76 F used a 392 head with K cylinders then the 77/78 F used the 410 head and matching cylinders.

My question is (without reading the whole thread): are you using the exact same setup that you had before you tore it down and if so did it leak like that before the tear down?

F2/F3 410 heads do NOT work with K cylinders but I can not give the exact reason without searching. Something about different/less/blocked, etc oil returns.

Do you remember seeing a recent thread about using the wrong taller length cylinder to head dowels?

[Elan]

You don't have a "F" head, you have a F2/F3 head. Remember, F's were made from 1/75 until the end of the 1978 production run and the 75/76 F used a 392 head with K cylinders then the 77/78 F used the 410 head and matching cylinders.

My question is (without reading the whole thread): are you using the exact same setup that you had before you tore it down and if so did it leak like that before the tear down?

Do you remember seeing a recent thread about using the wrong taller length cylinder to head dowels?

The bike was running crappy when I got it. Cylinders 1 and 2 werent firing.  I saw it run for a minute, and didnt notice any leaking.  Im doing the same setup except i added 836cc pistons.

Ill search for the thread you are speaking of.

[Elan]

You don't have a "F" head, you have a F2/F3 head. Remember, F's were made from 1/75 until the end of the 1978 production run and the 75/76 F used a 392 head with K cylinders then the 77/78 F used the 410 head and matching cylinders.

My question is (without reading the whole thread): are you using the exact same setup that you had before you tore it down and if so did it leak like that before the tear down?

Do you remember seeing a recent thread about using the wrong taller length cylinder to head dowels?

SO i guess i have an f2/f3 head,  and 72 or 73k crankcase.  Not sure what the cylinders are.  I did buy K gaskets...

[HondaMan]

You don't have a "F" head, you have a F2/F3 head. Remember, F's were made from 1/75 until the end of the 1978 production run and the 75/76 F used a 392 head with K cylinders then the 77/78 F used the 410 head and matching cylinders.

My question is (without reading the whole thread): are you using the exact same setup that you had before you tore it down and if so did it leak like that before the tear down?

Do you remember seeing a recent thread about using the wrong taller length cylinder to head dowels?

SO i guess i have an f2/f3 head,  and 72 or 73k crankcase.  Not sure what the cylinders are.  I did buy K gaskets...

Did your "K" head gasket have the bigger ( holes that fit the rubber seals around the head dowels? The early "K" head gaskets don't have these dowels, and the holes in the head gasket (also on many 836 head gaskets) are too small. The small holes cause the head gasket to interfere with the sealing of the rubber dowels, and in at least one case it also prevented the head from seating all the way down onto those dowels.

I recently wrote to Cometic and Wiseco about this problem, as they sell head gaskets with their 836 kits that DO NOT have the larger holes (14mm) for the 8 dowel/seal arrangement on the post-K3 heads. I have always had to punch them out with a 5/8" punch, myself. Wiseco is asking Cometic to consider making the proper gasket available: if you have the opposite arrangement (the later head gasket with the earlier cylinders and head) then you can just drop a 1.5mm thick x 12mm O-ring in the gasket to seal it up.

About 4 weeks ago I tore down an 836 that was suffering massive oil leaks around the head from this very problem. He got the new head gasket from Cometic, but it was like his first one from Wiseco: the holes were small. I think I have a post here somewhere about punching those holes out as I did it? What happens is this: the rubber seals get trapped underneath the head gasket when the holes are too small, and the gasket is not designed to seal oil around those holes very well. It usually takes some added sealant (Permatex non-hardening is OK here) to seal those holes on these non-saturated 836 gaskets. By comparison, the Vesrah and Honda head gaskets are permeated with a waxy sealant that melts out and seals small gaps after the engine heats up a time or two.

But right now, I am leaning toward MC's suggestion that the timeserts and/or pucks could not hold back against the higher pressure oil that was escaping from the cam bearing's feed hole...

[Elan]

Ok, so I guess ill try:

adding the 2 missing o-rings
gob some sealant over the time-serts
get new pucks since they are covered in dried sealant
lots of thread sealant on the 4 cam tower bolts
replace stud washers with copper ones (will I need a new head gasket if I do this?)
Should I check the dowels/rubber at the head/base gasket? or are they not a concern since the gaskets arent leaking?
Should I get a new head?

I'd rather play it on the safe side than risk pulling the engine a fourth time!

[Jerry Rxman Griffin aka MuthaF'er]

Find the thread(s) about matching the F2/F3 cylinders and head to be sure you have the proper cylinders.

[Elan]

Find the thread(s) about matching the F2/F3 cylinders and head to be sure you have the proper cylinders.

Got it.  I'll need to identify what my cylinders are...

[Kevin D]

Im no expert on any of this stuff, but I've read a few things from the manuals here that might be helpful, about the oil returns.

 From the Technical page, I've added a photo showing cap nuts on studs 5-6-7-8 for a 750F head.http://www.sohc4.net/?p=249
 From the F2 supplement, page 30 of 40, it shows dowels and stud bolt packings only at studs 9-10-11-12. http://data.sohc4.net/HSMCB750F.pdf
This info is telling me that the F gravity oil returns are on studs 9-10-11-12 only, and not  5-6-7-8-9-10-11-12 like the earlier bikes.

I have a hose connected from the back of the crankcase to the bottom nipple on the oil tank. Is that correct?

Yes

I have a hose connected from the valve cover to the nipple on the top of the oil tank. Is that correct?

I don't think so - my engine vent hose goes down towards the swing arm, as does the top oil tank vent hose.


So..... I'm thinking maybe the oil thats returning down studs 9-10-11-12 is getting blown back up and out studs 5-6-7-8 because of mismatched pieces and incorrect breather.
Did you have the cap on the oil tank when you made the video?

[Elan]

Im no expert on any of this stuff, but I've read a few things from the manuals here that might be helpful, about the oil returns.

 From the Technical page, I've added a photo showing cap nuts on studs 5-6-7-8 for a 750F head.http://www.sohc4.net/?p=249
 From the F2 supplement, page 30 of 40, it shows dowels and stud bolt packings only at studs 9-10-11-12. http://data.sohc4.net/HSMCB750F.pdf
This info is telling me that the F gravity oil returns are on studs 9-10-11-12 only, and not  5-6-7-8-9-10-11-12 like the earlier bikes.

I have a hose connected from the back of the crankcase to the bottom nipple on the oil tank. Is that correct?

Yes

I have a hose connected from the valve cover to the nipple on the top of the oil tank. Is that correct?

I don't think so - my engine vent hose goes down towards the swing arm, as does the top oil tank vent hose.


So..... I'm thinking maybe the oil thats returning down studs 9-10-11-12 is getting blown back up and out studs 5-6-7-8 because of mismatched pieces and incorrect breather.
Did you have the cap on the oil tank when you made the video?

So the valve breather goes to nothing, and the top oil nipple goes to nothing too?  I think this might be the eureka moment.

The oil cap was on in the video.

I feel like the mismatched head isnt the issue (but could be wrong) because the previous owner said he had been riding the bike all summer and never did any work, until it stopped working hehe.

It sure did look like oil was blowing up studs 5 and 7... So that theory is possible? because it definately seems logical...

[MCRider]

Just to confirm the breather routing, and nothing else. Yes, the breather from the valve cover and from the top of the tank, both hang together at the back of the engine, not connectred to anything else. On the earlier 750s. Later they are run into the airbox for EPA compliance. You'd know if that was which you have. And if you don't have an airbox, its moot, revert to the old routing.