Topic: 1972 Honda CB750 K2 Head Gasket Leak: Vendor suggestions!

[BikerBrains]

I have a few Hondas <1975 and I know the "pucks" leak, you know, those little round rubber things under the Cam Towers. Well Im sure mine are but I think the head gasket is leaking too.

Is there a vendor, a reputable vendor and brand, that sells all of the top end seal stuff in a KIT?? Im having someone I trust do the work because I dont have the time.

What else might I need? Im guessing  - Valve cover/rocker arm cover gasket - Head Gasket - Oil passage o-rings (2) - Oil line o-rings
- Tach cable seal

Anything else?

[cfairweather]

In my humble opinion, Cycle-X sells the best gaskets.  The other brands will work, but Ken sells the best ones in a kit. 
He will give you a choice on the head gasket and I recommend the multilayer metal one he sells. 

[BikerBrains]

In my humble opinion, Cycle-X sells the best gaskets.  The other brands will work, but Ken sells the best ones in a kit. 
He will give you a choice on the head gasket and I recommend the multilayer metal one he sells.

DUUUUUUDE! Minutes after I posted this I went to CycleX, remembering that I bought stuff from them years ago! They even have "pucks" that are made of metal and replace the old rubber ones. The Kit that I am getting is the $229 one, this one below:

[bryanj]

Personally i would lift the barrels and replace the base gasket as well due to it being loosened when head bolts loosened

[PeWe]

MLS head gasket need higher torque  to seal. Like 22 ft lbs.
Heavy duty cylinder studs are probably a must too. They are more rigid and do not flex as stock do.

My CB750 K2  ( later head ) last head gasket is from a Vesrah kit. It works fine. I tightened ca 20 ft lbs. I used the 8 oil return o-rings too.

Checked nuts the day after and they did not move when I tried the same torque again. I loosened one by one 1/4 turn and tightened again.

I like Honda gasket for all engine covers. All the holes sit where they should.
Cheap aftermarket gasket must get a few holes corrected by a sharp knife.

[cfairweather]

1.  Yes, I agree with using heavy duty studs.  I have found that either brand, APE or Kibblewhite are fine, but I think the APE might be slightly stronger.  I just had a Kibblewhite break before it reached 20 lbs yesterday.  I ordered a new APE set from Randakk for $122.00.  I don't recommend reusing these studs as they seem to weaken after the first use.  Cycle-X sells Kibblewhite.
2.  After you torque the heads to about 18lbs, use a propane heater (tube type) and heat the head/cylinders up to operating temp to simulate a heat cycle.  Let it cool overnight, and the next day retorque to 18lbs and you will find some of the nuts will tighten up some more.  Then finish torquing to the final value. 

[scottly]

1.  Yes, I agree with using heavy duty studs.  I have found that either brand, APE or Kibblewhite are fine, but I think the APE might be slightly stronger.  I just had a Kibblewhite break before it reached 20 lbs yesterday.

A "heavy duty" stud broke before 20 ft/lbs and you think they are a good idea? Has anyone ever had a stock stud break, other than when trying to remove them?

[PeWe]

I snapped an APE cylinder stud 2014.
The reason was a bad torque wrench I have borrowed.
I ordered new wrenches from Germany, decent quality for not much,  brand Hazet.

I tested the other tightened nuts with the new wrench. Nut started to move at 36Nm when tightening. (26.55 ft lb)

I had tightened 28Nm (20.68 ft lb) with the bad tool that must been a bit over 30Nm
Over the max limit of 22.5ft lb (30.5Nm), thats for sure.

So not strange it snapped.

I replaced all studs after that. Kibblewhite went in. Those have seen several heads and many head tightenings since then.

My K2 got APE studs later on.

Important with a correct tool.

It was another thread in this forum 2014 about a guy that had snapped a cylinder stud. He replaced only the broken one.

Another stud snapped while riding ending up in ruining the engine. Broken cam, cracked case etc etc. Happy to not crash and  cracked himself.

That helped me in the decision to replace all my studs. They have all  been overtightened.

[HondaMan]

PM me your address. The #1 leak in the modern head gaskets (for ALL these SOHC4 bikes) is those 2 O-rings that pass the oil ports thru the head gasket. I'll send you 2 special ones that are thicker, because 100% of ALL head gaskets for these bikes got 0.2mm thicker (some even more) when asbestos was outlawed in the 1990s.

Also: if you pull off the cylinder for new pistons, get the cylinder's deck milled 0.010" down when they bore for the pistons, which will also help prevent this leak. Make the piston clearance LESS than 0.0010" (0.0006"-0.0008" is my go-to range) or the new piston rings will not seal well.

(See my book for many more tips!)

[scottly]

It was another thread in this forum 2014 about a guy that had snapped a cylinder stud. He replaced only the broken one.

Another stud snapped while riding ending up in ruining the engine. Broken cam, cracked case etc etc. Happy to not crash and  cracked himself.

There have been several cases of "heavy duty" studs snapping over the years, both APE and Kibblewhite. Also, doesn't the MLS gasket require a very smooth finish, meaning the cylinder deck and cylinder head need to be re-surfaced?
http://forums.sohc4.net/index.php/topic,77878.msg868694.html#msg868694

[PeWe]

It was another thread in this forum 2014 about a guy that had snapped a cylinder stud. He replaced only the broken one.

Another stud snapped while riding ending up in ruining the engine. Broken cam, cracked case etc etc. Happy to not crash and  cracked himself.

There have been several cases of "heavy duty" studs snapping over the years, both APE and Kibblewhite. Also, doesn't the MLS gasket require a very smooth finish, meaning the cylinder deck and cylinder head need to be re-surfaced?
http://forums.sohc4.net/index.php/topic,77878.msg868694.html#msg868694

Very smooth surface, yes.  No scratches.  Grit 400 smooth.
Cylinder has the same finish.

EDIT:
The old thread was from 2013

http://forums.sohc4.net/index.php?topic=131389.msg1465662#msg1465662

http://forums.sohc4.net/index.php/topic,125377.msg1424921.html#msg1424921

I tightened 29Nm. I reused that MLS gasket again tightened a little more next time. 29.5Nm (threads and under nuts lightly oiled)
Around 21.5 ft lb.  Torque wrench  specified to +/-4% when new.
This makes +/-  0.86 ft lbs. Close to max torque 22.5 ft lb

I hope the torque wrenches are still  OK. I release the setting direct after each use.

Nm vs ft lb
https://www.unitconverters.net/energy/nm-to-ft-lb.htm

[willbird]

MLS head gasket need higher torque  to seal. Like 22 ft lbs.
Heavy duty cylinder studs are probably a must too. They are more rigid and do not flex as stock do.

My CB750 K2  ( later head ) last head gasket is from a Vesrah kit. It works fine. I tightened ca 20 ft lbs. I used the 8 oil return o-rings too.

Checked nuts the day after and they did not move when I tried the same torque again. I loosened one by one 1/4 turn and tightened again.

I like Honda gasket for all engine covers. All the holes sit where they should.
Cheap aftermarket gasket must get a few holes corrected by a sharp knife.

Do any of the mfg specify whether to lubricate the threads where the nut goes on ?? Good quality studs should NOT break. They should have a rolled thread. There was a YouTube vid I watched recently where they were making studs, not remembering the mfg.

A grade 10.9 8mm bolt should be able to lift 38,100lbs, 30,500lbs would be a "proof load". Not readily finding the exact load in lbs to achieve yield but 970MPA is proof, 1100MPA is yield, 1220MPA is minumum tensile. So those numbers show a 10% difference between tensile and yield so about 35k lbs yield maybe ? Must be torsion breaking them maybe.

Torque to tension is not linear but torques of 20.2 ft lbs lubed, 22.9 zinc plated, and 26.9 dry all net aprox 5123lbs clamping force.

Bill

Bill

[PeWe]

I use motor oil as my engine get.
It feels better when  tightening.

Not the anti friction stuff as Molycote 1000 which might be old stuff today.
If that is used lower torque needed.

[willbird]

I use motor oil as my engine get.
It feels better when  tightening.

Not the anti friction stuff as Molycote 1000 which might be old stuff today.
If that is used lower torque needed.

Some race engine shops use a LOT of this stuff.
https://www.rbssuperchargers.com/Products/Detroit_Diesel_Peanut_Butter_Engine_Assm__Lube--2600-0155

Bill

[paul_cb836]

My 915 race motor has the same HD studs fitted when the motor was first built 15 years ago. Don’t know which studs - purchased from Dynoman. This motor has been rebuilt at least half a dozen times, if not more, and never had a problem.

[cfairweather]

Quote
I snapped an APE cylinder stud 2014.
The reason was a bad torque wrench I have borrowed.
I ordered new wrenches from Germany, decent quality for not much,  brand Hazet.

I decided to check my HF click type torque wrench before I torqued my new APE studs and discovered it is bad.  At 5lbs, it is actually applies about 9lbs.  So, I will be buying a new torque wrench today.  Maybe the ICON brand from HF. 

[HondaMan]

Quote
I snapped an APE cylinder stud 2014.
The reason was a bad torque wrench I have borrowed.
I ordered new wrenches from Germany, decent quality for not much,  brand Hazet.

I decided to check my HF click type torque wrench before I torqued my new APE studs and discovered it is bad.  At 5lbs, it is actually applies about 9lbs.  So, I will be buying a new torque wrench today.  Maybe the ICON brand from HF. 

If you can locate a Craftsman (beam type is best), try for one of those instead. I have not seen ANY torque wrench from HF that is even half-close to right - even their beam version.

[cfairweather]

I haven't bought a new torque wrench yet, but for now, I returned the HF faulty one and bought a HF Quinn 3/8 in. Drive, 5.9 to 59 ft-lb Digital Torque Adapter so I could torque the head.  This only cost about 20 bucks after my exchange, but I really don't fully trust it yet.  I could not bring myself to torque the head over 20 lbs.  I will take a look at the Craftsman line, but I have been very impressed with the ICON tools at HF.  I am in no hurry for now, but I can tell you it will not be a cheap one.  Here is the digital torque adapter that I used:
https://www.harborfreight.com/38-in-drive-59-to-59-ft-lb-digital-torque-adapter-58705.html

[HondaMan]

Although I'm speaking from a very-much experienced seat here, I've found i can often tell within 10 in-lbs where I torqued a head or crankcase bolt on the 750 and the 500/550 Fours. I still remember doubting how it felt when I used a brand-new HF 'click' wrench I borrowed to try out, and how the engine weeped oil from the head gasket in less than 1 minute after startup. I shut it off and pulled the #1 plug to insert a long socket on the stud there and test the torque with my "old trusty" beam wrench (from 1969) and found it started turning at about 80 in-lbs indicated. After I disassembled everything and re-pulled the engine from the frame I found every bolt, even the 6mm ones, were all way too light and ended up disassembling the whole engine again and eating a gasket set. I later told the owner of the HF wrench about it: he ignored it until he also got stung by it when assembling a machine that had to be torqued right or else gunpowder would find its way out of the sluices that loaded the large shells the machine made: when that powder started showing up all over the floor and the top of the machine, he decided maybe I was right - and then he threw them out and called Snap-On for an expensive set.