Topic: Needing some opinions...APE/HD cyl head studs, leaking head gasket CB750

[Eydugstr]

Been dealing with a persistent oil leak issue on a '72 CB750, with about 400 miles after a rebuild, stock pistons & cam.  Awhile back, it develop a leak coming from the cam cover, narrowed it down to being the rubber pucks, and shimmed them as per Hondaman's recommendation.

Went to fire it up...No leaks from the cam cover, but now leaking from the head gasket  .  When I had rebuilt it, used a Cycle X (non MLS) head gasket & permatex copper spray (as per their website), and used the stock studs, washers & nuts.  Didn't know about the cylinder head retorque until afterwards (Hondaman's book, nor the Haynes or Clymer make any mention of re-torqueing!)

So my questions would be...I've noticed APE & HD studs on a lot of sites, are they meant for leak prone engines, or are they mainly intended for bored out/high performance motors?  If your bike has a frame adapter, can they be changed out with the motor in the frame?

Also, found a "re-torque" sequence with the thread seach - http://forums.sohc4.net/index.php?topic=41730.msg430782#msg430782 Noticed they've got a top rating of 22 ft-lbs of torque, where all the books I've got are stating 15.2 ft-lbs tops.  Is the 22 meant for the HD studs?

Because Honda discontinued their head gasket, what's everyone recommending now?

[flybox1]

where on the head gasket is it leaking?

[flybox1]

I used the head gasket that came in the vesrah kit, nothing special, and coated it with copper spray.
HD Studs & nuts.
3 step torque sequence to 22ftlbs, overnight rest, loosen, and then another 3 step torque, up to 22ftlbs, and no leaks.....

[Wobbly]

Same problem with the Cycle X MLS gasket a few hundred miles after rebuilding. I now opted for the original Honda gasket which is still available from the usual NOS places (not cheap though).

[iron_worker]

I also have a leaking MLS gasket ... my parts and install sequence:

-APE studs
-surfaced head and cylinders
-MLS gasket from Cycle X
-Torqued to 18ft*lb (had one stud with a questionable thread so I wasn't sure about going any tighter)
-Let sit overnight and then loosened and retorqued each nut one at a time in sequence

So I know by not going to the high torque rating I may have somewhat defeated the purpose of having the stronger studs so I'm not sure if that's what is causing my leak or something else.

I'm also suspect of my torque wrench since it's a cheapy so if I do it again I'll be either testing mine or buying a higher quality one.

One other thing I guess I probably screwed up was that I ended up having to tear the head off once after I had already torqued it all up (had to repair one thread). Ken at Cycle X says so long as you haven't heat cycled it then you should be OK so I re-used that gasket.

So I'm not too sure where I failed but looks like I'll probably be trying again. I'd like to hear of guys' success stories with MLS gaskets if they are out there. Not sure if I should go back to it or not.

Another thought I had was maybe next time I would set up some type of "oven" using a cardboard box and a heat gun to heat cycle the engine a few times artificially so I can then retorque the head without having to take the engine out of the bike.

IW

[Eydugstr]

Okay, TY.  Was wondering if people were running into the same problems with the MLS gaskets, too.  Will be on the hunt for an NOS Honda head gasket (preferably one that isn't bent like the last one I found!)

Next question....When using the Honda head gasket, do you still have to re-torque?  If so, is it just to the 15 ft-lbs, in steps?

[Old Scrambler]

Did you seal the threads on the cam-tower cap-bolts?  I did not do mine and it LOOKS likes a minor gasket leak. Teflon or BLUE lok-tite will do the job.  My recommendation is stay with the stock studs.............but change the nuts to the HD units (extra thread but 13mm wrench) from Cycle-X..........and final torque to 17-lbs. If they fail you will know you need the APE units. 

Torquing involves stretching the threads on the studs. When the motor is going through a heat cycle, the studs are meant to stretch, which is what the stock units are designed for. When you took your motor apart, was it slightly warped? Hopefully you had your head skimmed to make it level before you put your motor back together. If not, some of the torqued studs are trying to pull the head straight and may not be properly sealing the head gasket.   

[Eydugstr]

This time around the leak came from underneath the head, so I'm pretty sure it's the gasket.  Will also do a compression test and see if that shows me anything.  The cam cover stayed dry this time, so hopefully the rubber puck shims were the cure there.   Last time I used blue loctite on the cam tower bolts.  Will also pick up a set of the Cycle X HD nuts, seem pricey but hey if it fixes the problem without having to risk removing or breaking off part of a stud, I'm all for it.

Yes, both the cylinder head and cylinder block were machined flat by a local machine shop.  Once I get the head off will double check it again.

[Bailgang]

I had no leaks at all when using CycleX MLS head gasket on my 550 but we're talking 750's here. On my current 750 F2 I used NE brand gaskets on it, a bit of copper spray on the head gasket, pitched the nitrile o-rings that came with the kit and used viton o-rings instead. I've got about 3k miles on the engine so far and the only leak I have is a pesky oil pan drain screw that's leaking a bit but I just got a new copper crush washer for that today. Other than the leaky oil pan drain screw the engine is clean.

[mark52]

Eydugstr you my also want to check the length of the dowels since you mention that the machine shop machined the surfaces flat.

[Jerry Rxman Griffin aka MuthaF'er]

Doug, the 22 ftlbs is for the APE studs, not stock studs.

The APE studs are intended for any engine but are designed to take more torque to hold things tighter regardless of what's inside but are a better option for most high performance.

My take is a re-torque is a smart idea. I think it's not mentioned as it's impractical in most cases unless a frame kit is installed.

Did you torque the head in the proper sequence the first time? If not perhaps the seating is not even across the head?

Does your head use the sealing washers around the studs?   

Have you re-checked the current torque on the nuts? You might want to see how tight they are NOW out of curiousity. Perhaps the gasket compressed and it's a little looser? When I took mine apart after many abused miles I had a couple nuts that didn't even need much wrench and some that were barely tight but I suspect that was due to stretch.

[Bailgang]

Eydugstr you my also want to check the length of the dowels since you mention that the machine shop machined the surfaces flat.

+1 Good idea.

[Eydugstr]

Doug, the 22 ftlbs is for the APE studs, not stock studs.

The APE studs are intended for any engine but are designed to take more torque to hold things tighter regardless of what's inside but are a better option for most high performance.

My take is a re-torque is a smart idea. I think it's not mentioned as it's impractical in most cases unless a frame kit is installed.

Did you torque the head in the proper sequence the first time? If not perhaps the seating is not even across the head?

Does your head use the sealing washers around the studs?   

Have you re-checked the current torque on the nuts? You might want to see how tight they are NOW out of curiousity. Perhaps the gasket compressed and it's a little looser? When I took mine apart after many abused miles I had a couple nuts that didn't even need much wrench and some that were barely tight but I suspect that was due to stretch.

TY, Jerry.

When you say sealing washers, are you referring to the metal washers underneath the 16 cyl head nuts, or are you referring to the rubber sleeves that went around the studs on the later models?  The cyl & cyl head on mine is a '72 K2, the one that uses the smaller cam tower O-rings, and no rubber sleeves.  No, I didn't use new metal washers under the cyl head nuts (just like the re-torque...no warning about it in manuals, and didn't appear to be made of a crushible metal like copper or aluminium).

No, I haven't rechecked the current torque yet, haven't had the cam cover off yet.  When I had the cam & towers off for re-doing the rubber pucks,  rechecked the torque then, however.  Yes, all torqued in sequence as per Hondaman's book.  Right now my game plan is to do a compression check,  and get my ducks in a row.

mark52 - No I didn't check the length of the dowels when I put it back together the first time...I'll double check them this time, though, and make sure there's more than enough clearance to account for the heads being surfaced.

Haven't bought a set of APE studs yet...If I wind up not finding anything else, will go that route.  Does the retorque still apply for the OEM honda head gaskets, with their bonding coating, or is this mainly for the aftermarket head gaskets? 

Can't believe how people would put up with this back in the day, with no frame adapter.


   

[Jerry Rxman Griffin aka MuthaF'er]

I would re-torque regardless of which gasket if I have access. Can't hurt. May find it's fine, may get a little more tightening.

Yeah, I was referring to the 'sleeves' as you called them. They seal the oil passages. Shouldn't need new metal washers under the nuts. If you'll notice they have a down side and an upside with a slight rounded edge (if I remember correctly) but can't say if that really matters.

Keep in mind that there are 2 different length dowels that have the same diameter.

[Nic]

I posted a little while ago about my head nuts, I had only 2500Ks on the new 750 K2 build but had to pull the engine down again as there was a whine in the tranny, I decided to do the ebay flat top 836 kit while I was at it. The bike is up n running now with only about 500Ks so far.
When I got to removing the head it felt like the nuts wouldn't have had 5lbs on them, the 6x6mm bolts were all but loose, this to me is hard proof that re-torquing is a necessity. As loose as everything was I still had no oil leaks, stock studs torqued to 15ftlb. I've got Frank's frame kit so I'll be re-torquing soon. It's a bit of a job as you have to remove all the cam gear to get at everything, under the pucks as well. I have always just used stock type head gasket and sprayed silver metallic paint on them before fitting, never used copper but if you seal the cam tower studs and the pucks you shouldn't get leaks. If my engine was still not leaking with all but zilch torque I'm more than happy to use the stock studs and 15lb torque but re-torquing is absolutely needed IMO.

[seanbarney41]

Let's try and be really specific and accurate with our wording here...when talking about re-torqueing...are you referring to letting the head sit 24 hours and then re-torqueing, or running the motor, heat cycling it, and then re-torqueing?

[Nic]

If you're referring to my post, I'm saying put some miles on it n then re-torque. In my case about 500Ks should be a good time to do it.

[Eydugstr]

Let's try and be really specific and accurate with our wording here...when talking about re-torqueing...are you referring to letting the head sit 24 hours and then re-torqueing, or running the motor, heat cycling it, and then re-torqueing?

That's a good question...From what I've read on the forum (think it was a thread with Elan's bike) I thought re-torqueing was letting it sit for 24 hrs then rechecking the torque. 

From what I can tell now, there's other threads that say to loosen the cyl head nuts, the re-torque in increments back up to the torque spec.  When the words "heat cycle" come into the picture...That means we've got to run the bike, remove the cam cover, cam & cam towers   and then re-torque...

Did Honda put out a service bulletin on this?  Granted, I understand talented wrenches are going to experiment, and see what solves the problem and in the process everyone comes up with a different approach...But I think SeanBarney is right for trying to keep everyone on the same page.

[PeWe]

HD studs are stiffer, not as flexible as the OEM studs when torquing more than Honda manual say.
Do not torque too much, they can snap. Max is 22.5 Ft lbs. Keep margins when your too might not be perfect calibrated
Not fun if stud snap when driving. There is a thread about that. My stud snapped in the same way, direct under then nut that can fall in the engine if happen when driving. No high CR, no meaning to torque over 20 ft lbs. I torqued 21.5 ft lbs (28Nm) when I have 836 with higher CR. kibblewhite HD studs + HD nuts (std DIN6331)
- I used Std Cometic fiber gasket with mentioned copper spray on both sides. This gasket has no room for 8 thick O-rings for oil transport.
-Why buy expensive HD nuts??? Standard DIN6331 is forged nuts of grade 10. Available workd wide for not much money. I used them with thinner washer to allow max thread contact

MLS gasket demands very fine surfaces on both sides.
Rubber pucks, leaking studs for cam holders (if removed and fastened again without thread lock)

- If you use the 8 thick o-rings with special pin that can be too long/wrong seated? Or with a gasket with small holes that should not have these as the Cometic fiber AND MLS.
http://www.yamiya750.com/index.php?main_page=product_info&cPath=21_54&products_id=707
http://www.yamiya750.com/index.php?main_page=product_info&cPath=21_54&products_id=1712

[flybox1]

+1 to brandEn's 'leak free top end' thread!
Its not just the stud stretch, you are also getting the squish out of whatever gasket you are using....the 3-stage torque, 24hr rest, loosen, and the re-do the 3-stage torque was very easy to do.  The time in between torquings allowed me to get my valve train out and ready to go, get my pucks properly gooped and set, and revisit my HM book to make sure ive got my head straight 
 

[Jerry Rxman Griffin aka MuthaF'er]

Let's try and be really specific and accurate with our wording here...when talking about re-torqueing...are you referring to letting the head sit 24 hours and then re-torqueing, or running the motor, heat cycling it, and then re-torqueing?

What I meant is to run the engine then go back and re-torque. Letting it sit for 24 hours and re-torqueing might provide beneficial results but not like the real thing IMO.

I agree with Cal about anecdotal. otherwise you must totally build 3 identical engines for comparison and try both methods plus not loosening the nuts as in the method he mentions, just tightening again.   

[Eydugstr]

TY for the responses, everyone.

[PeWe]

I re-torqued after 24 hours. One by one, loose 1/8 turn+ re-torque with same ft lbs/Nm as before
One month later and some driving, changed cam + cam holders and could not resist to check torque again. Some nuts were really loose! No leaks though. I do not know if the Cometic fiber gasket shrank or if the 2 knock pins somehow blocked head assembly.
(I have not the 8 special pins inside 8 thick o-rings when the gasket has smaller holes)

Easy for me when I have done the frame kit supplied by 754 on this forum making it possible to lift head cover, head, cylinders without taking out the engine out of the frame. Pulling the egine is not the worse thing.... all stuff that have to be made before that point and back again....

I take out a small part of the frame away from the engine... 

[Nic]

I re-torqued after 24 hours. One by one, loose 1/8 turn+ re-torque with same ft lbs/Nm as before
One month later and some driving, changed cam + cam holders and could not resist to check torque again. Some nuts were really loose! No leaks though. I do not know if the Cometic fiber gasket shrank or if the 2 knock pins somehow blocked head assembly.
(I have not the 8 special pins inside 8 thick o-rings when the gasket has smaller holes)

Easy for me when I have done the frame kit supplied by 754 on this forum making it possible to lift head cover, head, cylinders without taking out the engine out of the frame. Pulling the egine is not the worse thing.... all stuff that have to be made before that point and back again....

I take out a small part of the frame away from the engine... 

+1 exactly what I said in my post #14, put some miles on and re-torque then. I reckon the gasket must shrink down with the miles. ALL my nuts and 6mil bolts were very loose but still no leaks. On first build I put the 8 rubbers and pins in, this time I left them out.