Topic: aNother leaking head! -- The 750

[Pecantree]

So I've got about 2000 miles on the bike after the engine rebuild + the crash and front end rebuild.
This is all K6 except for the engine case itself which is a K3
ALL rubber o-rings, seals and gasket sets were new from cycle-x.
It has Ape HD cylinder studs.
The top end had "The Leak" starting about 2 or 300 miles in. In the last 500 or so miles it's been getting much worse.
The engine was leaking from the left side.
So Monday decided to pull the engine and fix it.

I like the pipe method, once everything is unbolted it only takes about  5 minuets to pull the engine.

Didn't picture the cover gasket but it looked good and dry all around.
Screws were all tight.
This is a down shot of #3 and #2 sparkplug wells.  1 & 2 were both oily, 3 & 4 were dry and clean.


Here are 3 pictures of front of cylinders 4,3 - 3,2 - 2,1.






A little better picture of the cylinder fins.


Top of the head.
The 6 pucks were dry in the middle when I pulled cam carriers off and they were the good ones from Cycle-x.
I had installed these with the non hardening sealant per Mark's book.
The four cam tower studs have not been removed.
All 16  nuts holding the head down were tight
The first two 6mm bolts  indicated by the red arrows were loose, only finger tight.
The third one was tighter but not full torque. The 4th was full torque.
At the top left you can see a screw that holds on the #2 exhaust spigot. It was loose and this screw was bent.
Bad, but that wouldn't cause an oil leak.


The oil jet o-rings by 2 & 3 intake valves were abraded as shown like this picture.

The outer o-rings were fine.

Just for grins here is the underside of the head 1&2, 3&4.



After cleaning gasket off the head I measured with a straight edge and could not get a .003 in.
Stev-0 looked at everything and suggested I post with pictures. (ask him about his tank!)
There is some oil on the front of #4 at the engine/cylinder joint. You can see some of it in the third picture.
I've got a very leaky right side fork seal and think some of this oil is from that.
Here's a shot straight down the cylinders.

This bike has run well since the rebuild but I've never got good mileage from it. Averages about 32.
I've ordered new gaskets and rubbers from cycle-x and new nuts,washers and the 4 6mm bolts for the head.
During the rebuild i reused the old bolts.
I hope the leak was from the loose 6mm head bolts. I'm not sure why the 0-rings for the oil jets were so chewed up,
But I'm glad I caught it.
What do y'all think.
Thanks
Steve

And here's a wolf chasing a motorcyclist in BC.

[HondaMan]

It appears the O-rings for the oil jets are too big! I don't think I've seen that problem before. Honda's spec is 1.9 x 5.9 mm there, and the 2x6 works OK as well. Check your depth in the groove: around the oil jet itself it should be 1.6 to 1.8mm deep. I have seen them at 1.4 and 1.5mm deep, usually on the post-1976 engines like the F0/1 and K7: on those I use the 1.9 x 5.9 O-rings for a little less bulk. Maybe yours are shallow, and the O-rings are 2x6? That would let some material get squeezed too far out and pinched, giving it the abraded look.

The head seals in the holes between the cylinders and head: there are some out there that are tapered in a sharp angle, instead of being flat on the ends like Honda's (or Vesrah's) were/are. I have not had any good luck with those sealing, at all.

Another thing: the head gaskets we are getting today do not have any of the OEM seal 'stuff' that used to be painted on the surface, and impregnated around, the 8 oil passages and the 2 oil feed passages. This causes leaks. At the time of my book, Honda still sold their head gasket and the Vesrah ones in the kit(s) shown in the book all had this sealant: I have not seen it now in about 3 years since. I have been adding either Hondabond or a paint-on sealant in those areas lately, to preclude leaks.

The worst leakers today: Cometic head gaskets. If you have one of those, seal everywhere with Permatex non-hardening sealant.

[Wobbly]

Another thing though: you need to re-torque after 500-600 miles. Unfortunately, this means that the engine needs to be pulled again. If you don’t, it’s a gamble. Then, at least, let the engine sit for a day or two and then re-torque before putting it back into the frame.

[Stev-o]

Pecan - I didn't notice the chewed up o rings, that is odd.

Mark has given you some great info, so sealant may be the answer.

Mark - what is your take on re torquing  the head?


Thanks.

[70CB750]

Subscribed

[Black 750K8]

Another thing though: you need to re-torque after 500-600 miles. Unfortunately, this means that the engine needs to be pulled again. If you don’t, it’s a gamble. Then, at least, let the engine sit for a day or two and then re-torque before putting it back into the frame.

If this has to be done I don't know how in the world an engine builder could back up his work. He could never hope for a leak free engine and then the customer would be very ill.

[CycleRanger]

Bummer about the leak. Great pix though! 

[Pecantree]

It appears the O-rings for the oil jets are too big! I don't think I've seen that problem before. Honda's spec is 1.9 x 5.9 mm there, and the 2x6

That's what I thought but they were from the kit. I'll measure depth when I get home.

Another thing: the head gaskets we are getting today do not have any of the OEM seal 'stuff' that used to be painted on the surface, and impregnated around, the 8 oil passages and the 2 oil feed passages. This causes leaks. At the time of my book, Honda still sold their head gasket and the Vesrah ones in the kit(s) shown in the book all had this sealant: I have not seen it now in about 3 years since. I have been adding either Hondabond or a paint-on sealant in those areas lately, to preclude leaks.

A local builder recommended to copper spray the gaskets. 3 coats drying, between each coat. I did this.

Another thing though: you need to re-torque after 500-600 miles. Unfortunately, this means that the engine needs to be pulled again. If you don’t, it’s a gamble. Then, at least, let the engine sit for a day or two and then re-torque before putting it back into the frame.

During first rebuild I torqued the head down and then left it for a day. Came back the next day checked the torque/re-torqued.
I've since heard that after a day you loosen the head and then re-torque.
What is correct?

Thanks for the input!
Steve

[Jerry Rxman Griffin aka MuthaF'er]

Retorqueing is theory and good theory but impractical. How many new owners took their bike back to the dealer for an engine removal and retorqueing! Letting them sit for a day then retorqueing has become commonplace. Plus I think you mentioned HD studs? 22Lbs torque? That gets the head pretty tight!

I haven't seen a gasket set that is labeled with useage locations but I have seen sets with 2 sizes of little orings. Did you perhaps use orings that fit another location like the advancer shaft etc?

[evanphi]

I have a leak that sits on my top fins. I'm keeping an eye on this thread!

[Wobbly]

I do not want to start a debate. It's like religion: believe what you want.
This is my experience, yours might differ:
30 plus years ago, every Honda dealership that I knew--and I knew a lot--would ask their customers to come back after 500 miles to have the head re-torqued after the head gasket was replaced. This was the Honda shop procedure back then--at least in my part of the world. It was not just for Hondas or CB 750s in particular. Back then, it was common standard to re-torque an engine after headwork was done. Usually, it's not a problem. Only with the 750, it is such a big deal because in order to re-torque, the valve cover has to come off--which means the engine must come out again. Naturally, a lot of people didn't bother. No warranty from Honda though for their work, if you didn't come back to re-torque. Perhaps there is more than just a correlation between the many, many CB 750s that have sweating head gaskets and the fact, that re-torqueing is so difficult and thus not done.
Others would simply over-torque. How successful that is, or, if engines got damaged that way, I don't know. I would not do this. What I and others have observed, is that if you let the engine sit for a couple of days, it seems to settle. Or, at least, re-torqueing would show, that some nuts had loosened up a little bit just sitting.
I have seen it more than once, that simply re-torqueing an engine, would stop a gasket from sweating. Finally, modern day engines apparently do not need re-torqueing. Back in the 70s, it was common practice for engines--not just motorcycle engines. And, no, my memory does not fail me.
But, again, do whatever you believe. Not re-torqueing might work fine. Drunk driving might also work. But just because it does works once or twice, does not mean that it is generally a good idea or proves anything.
As a side note: this has been discussed previously in this forum more than once.
Finally, I ride my K7 for 36 years now. Before that, I had an F1. That does not make me a mechanic, but gives me some degree of experience regarding CB 750s. And, experience, I am trying to share. That's all.

[HondaMan]

Pecan - I didn't notice the chewed up o rings, that is odd.

Mark has given you some great info, so sealant may be the answer.

Mark - what is your take on re torquing  the head?


Thanks.

The re-torque is something I always do (unless it was a hasty racing job or something, which is a different world).

The things I have noticed in the last 5 or 6 years with the gaskets has made me try to think on things to do to help keep the seal, as Honda never had heads re-torqued on these bikes (nor did Kawi, Suzy, or BMW, can't speak much to Yamahas), and few of them leaked. BUT - their gaskets were ALL coated, both sides, with sealant that resembled rubber cement and/or paraffin. This goo really grips the metals, too, as many of us have discovered. When I just disassembled my engine this summer, it was 6 years since I last had the head off to look things over inside. The head slid off as if it was never torqued. It shows the beginnings of weep around the holes that drain to the case (mine does not have those superior rubber seals, just the gasket seal), and I did not add sealant to this gasket: it was a Vesrah gasket I had at the time, has no integral goo.

What I DID notice when I disassembled it: the inner 6mm bolts required 2 fingers on the T-wrench to loosen. That's also where the weeping passages were starting. The outer ones and the front/back ones were still fully 90 in-lbs tight, and dry there.

My new(er) thoughts on these goes back now to the days when we made copper head gaskets for the real high compression engines. They sealed not hardly...so, we used the non-hardening goo around the oil ports and would torque the head, wait 24 hours (or at least overnight if in a hurry), then, in reverse sequence, loosen all the bolts, starting with the 6mm bolts, about 1/2 to 3/4 turn, then re-torque in order again. The 6mm go tight last, starting from the front-back ones, then the inner, then the outer. I started doing this routine again on standard head gaskets, beginning in 2007. So far, I haven't seen nor heard of any leaks except one: it was (is, as it is coming back next month) a year-old 836 kit with a Cometic head gasket.

I should also say here: I have installed 4 Cometic head gaskets on 836 engines in the last 4 years. All 4 have now leaked: this one was the last one, so it's 100%. All the others leaked right away during the initial engine startup on my test jig, so they didn't leave my hands intact. I have been using the head gaskets from Cruisinimage for the 836 engines, regardless of compression: so far so good. They strongly resemble Vesrah parts. I am therefore not a fan of Cometic's 836 head gaskets in these engines.

[lucky]

I would like to add to make sure you check the height of the locating dowels(cylinders)
because if they are too tall, the head will not bolt down properly.

I believe that Cycle-x lets their engines sit and then re torque. But check their TECH TIPS section.

[Wobbly]

Honda never had heads re-torqued on these bikes (nor did Kawi, Suzy, or BMW, can't speak much to Yamahas

That is contrary to my own experience and thus simply not true. One ought to be careful with terms like "always" or "never."
As for BMWs: the BMW shop manual of a R 1100 S / R 850/1200 C / R 1150 GS, page 5, explicitly states that you have to re-torque after 1000 km (600 miles). And that just happened to be the first manual I looked at.

[Adam_F]

Definitely watching this one!

[CycleRanger]

Definitely watching this one!

I predict the retorque or not retorque debate will ultimately eclipse the original subject of this thread..   

[Jerry Rxman Griffin aka MuthaF'er]

No doubt whatsoever that retorqueing is good! Let's take a poll though of ORIGINAL OWNERS that were told to bring their NEW bikes back for body removal, exhaust removal, electrical removal, engine removal, top end tear down, cam removal, and cam towers removal in order to retorque a new unopened factory engine then reassemble everything.

NOT ME and I am an original owner. I fully agree with Hondaman who was one of those Honda mechanics that has verified this.

I THINK if you talk with Kenny at CycleX you would be told that he test runs his engine builds on a test stand which provides an OPPORTUNITY to retorque prior to OWNER INSTALLATION. Perhaps he does not retorque?

Retorqueing is best accomplished after the engine has had miles and heat cycles done but letting them sit and retorque later is better than nothing.

[MRieck]

Use MLS head gaskets and steel base gaskets and you do not have to think about re torquing anything. They crush and stay that way. Copper is the same way. Unfortunately copper seals combustion gases very well but not as well with oil.

[Don R]

I was going to ask Mark about the Cometic gaskets. I have a new MLS Cometic for my 836 still in the wrapper about to go on. I was hoping he wasn't referring to those.

[Bootlegger56]

Not too jump in and display my ignorance but having been in the process of evaluating a MLS head gasket replacement on a Toyota I read a significant amount of discussion about the required Ra of the gasket sealing surfaces.  I noted that most MLS gasket manufacturers specify very low finish specs for aluminum mating surfaces especially when an aluminum to steel application is involved.  I would be interested in hearing comments about the necessary surface finish for our bike applications so that I might store it away for my future reference.  I think it might be something to keep in mind if a resurface of both the block and head are not planned or if access to a shop that can meet those requirements is not available.  Or......is this a null issue?

[HondaMan]

I was going to ask Mark about the Cometic gaskets. I have a new MLS Cometic for my 836 still in the wrapper about to go on. I was hoping he wasn't referring to those.

I am not sure what the MLS gasket is?
The Cometics I used came with the Wiseco kits, or were purchased separately. They have small holes (like the pre-1973 head gaskets), which requires an expensive punch to enlarge them to the 14mm holes size, or else you must forgo the dowels and rubber seals in the post-1972 engines. If you attempt to install the gasket with the small holes on top of those dowels and seals, the head will not sit flush and cannot be torqued closed.

Three of the 4 I used were punched to the 14mm size. Two of those leaked right away during the test run. The third one was a K2 engine, so it went in as-is: it also leaked during the test run. The 3rd one was in a friend's bike: he assembled it himself, but didn't have the HD studs, so he brought the engine to me to have those put in. The dowels were holding the head open and had sort of started the punched holes the hard way: I finished them with the punch. The head gasket had not been compressed yet because of the dowels, so it was re-used, so to speak. This engine has a milled head (.040" removed) and lowered cylinders (.020") as it is a K5 or K6 block, so the dowels stood pretty tall and had to be shortened a little to fit right. This one went about 6000 miles before the leak became a big issue, but it let go all the way across the front of the engine at once.

[70CB750]

MLS = Multi Layer Steel. like here:

http://www.cyclexchange.net/High%20Performance.htm

[Wobbly]

I've since heard that after a day you loosen the head and then re-torque.
What is correct?

According to BMW manuals, you loosen one nut at a time and re-torque.

[MCRider]

The early CB750s pretty much all leaked. I was working in shops back then, in the parts dept, and we warranted MANY CB750 head gaskets. I was out of the game by K2 so don't know how long this situation lasted. I think the factory improved it to at least get the engine out of warranty period dry.

I bot my K1 new from the dealer where I worked, the Head Cheese began leaking right away. The mechanic talked me into just re torquing it which required removal but not full disassembly. He got paid for the full job. I got a leak free engine. Re torquing it worked.

Since then I built a few 750 and 836 and one 888 engines. None leaked or needed re torquing. All had HD studs and non hardening gasket sealer on the gasket.

Fast Forward to last year, my current project leaked upon start up. With a frame kit it was easy to re torque and that stopped it. Unfortunately I've had other problems causing it to smoke and I've had to disassemble it.

Don't know if this was addressed. IF the 4 6mm cam tower hold down studs have been removed and reinstalled, that is an invitation to leak out the stud holes which open to the atmosphere in the spark plug cavity, about halfway up the fins. This causes the most mysterious leak source which took me quite some time to figure out.

Could this be your source of leak?

[Bootlegger56]

Mark;  Is CruisinImage the same source you have been using for the inexpensive big bore kits?