Topic: brandEn's leak free top end thread = Tips, Tricks and Suggestion encouraged

[bytio]

That's it

[bytio]

You can see the front two o rings on ready for cylinder

[NobleHops]

Adding nothing but thanks for a great thread. Thanks to all that contributed to this.

[MessnerMoto]

Great thread!

Just one question... I am rebuilding f2 engine with 836 wiseco kit... I Have MLS head gasket and HD studs.

I know I should leave rubbers out(part 2 from picture)... I am just not sure should I leave pins(part 3 from picture) out also?

[flybox1]

Definitely leave those in.  Locating dowel to help align the head to the cyls.
If you have had your head decked, you will run into clearance issues and need to adjust these to ~10-11mm.

[madmtnmotors]

Great thread!

Just one question... I am rebuilding f2 engine with 836 wiseco kit... I Have MLS head gasket and HD studs.

I know I should leave rubbers out(part 2 from picture)... I am just not sure should I leave pins(part 3 from picture) out also?

Definitely leave those in.  Locating dowel to help align the head to the cyls.
If you have had your head decked, you will run into clearance issues and need to adjust these to ~10-11mm.

Item #3 is optional if you leave out the barrel seals #2. #3 just helps the seal hold its shape. Do not leave out the four locating dowels #9 (two on top, two on bottom).

[flybox1]

Item #3 is optional if you leave out the barrel seals #2. #3 just helps the seal hold its shape. Do not leave out the four locating dowels #9 (two on top, two on bottom).

Thanks for the correction, mad. 

[madmtnmotors]

Item #3 is optional if you leave out the barrel seals #2. #3 just helps the seal hold its shape. Do not leave out the four locating dowels #9 (two on top, two on bottom).

Thanks for the correction, mad. 

Happy to help. I know I have trouble keeping all of the little bits straight from time to time.

Don't forget those four fat little 5.5x3mm o-rings (#6) at the base of the cylinders on the studs where the abandoned oil returns are as well. 

[MessnerMoto]

Great thread!

Just one question... I am rebuilding f2 engine with 836 wiseco kit... I Have MLS head gasket and HD studs.

I know I should leave rubbers out(part 2 from picture)... I am just not sure should I leave pins(part 3 from picture) out also?

Definitely leave those in.  Locating dowel to help align the head to the cyls.
If you have had your head decked, you will run into clearance issues and need to adjust these to ~10-11mm.

Item #3 is optional if you leave out the barrel seals #2. #3 just helps the seal hold its shape. Do not leave out the four locating dowels #9 (two on top, two on bottom).

Thanks to all for help . I was also thinking that #3 is just there because of #2. So I don't see the point of putting #3 if I leave out #2. So I will leave #2 and #3 out

[RAFster122s]

Wouldn't you need to resize both #3 and #9 if the head and or block were milled to flatten the mating surfaces?

[madmtnmotors]

Wouldn't you need to resize both #3 and #9 if the head and or block were milled to flatten the mating surfaces?

Possibly. Depending on how much was removed from the head and/or cylinders the dowels can require shortening. I usually put the calipers to them and measure the bores to determine whether they need ground/filed/cut down.

[turkey4me]

No 8 O-rings on are listed as being 11 x 2.5mm.  Can anyone confirm if 11mm is the inside or outside diameter?  Buna or Viton?

[Bailgang]

No 8 O-rings on are listed as being 11 x 2.5mm.  Can anyone confirm if 11mm is the inside or outside diameter?  Buna or Viton?

Can't say whether the 11mm is the OD or ID but I used viton o-rings everywhere I could on my F2 3 years ago while following many of the tips on this thread. The only oil leak I had was from the rubber pucks under the cam cradles due to the thin pucks in the aftermarket gasket set I used, I swapped them out for genuine Honda pucks and no leaks at all since.

[lightsareout]

this is awesome, thanks for sharing

[flybox1]

No 8 O-rings on are listed as being 11 x 2.5mm.  Can anyone confirm if 11mm is the inside or outside diameter?  Buna or Viton?

11mm is the ID.  Use viton.

[MCRider]

No 8 O-rings on are listed as being 11 x 2.5mm.  Can anyone confirm if 11mm is the inside or outside diameter?  Buna or Viton?

11mm is the ID.  Use viton.

I think the 2.5mm is the cross section of the ring material. That makes the OD 13.5mm. OCICBW

[flybox1]

No 8 O-rings on are listed as being 11 x 2.5mm.  Can anyone confirm if 11mm is the inside or outside diameter?  Buna or Viton?

11mm is the ID.  Use viton.

I think the 2.5mm is the cross section of the ring material. That makes the OD 13.5mm. OCICBW

You are almost correct.  2(CS)+ID = OD   
2(2.5) + 11 = 16mm in this case 

[MCRider]

No 8 O-rings on are listed as being 11 x 2.5mm.  Can anyone confirm if 11mm is the inside or outside diameter?  Buna or Viton?

11mm is the ID.  Use viton.

I think the 2.5mm is the cross section of the ring material. That makes the OD 13.5mm. OCICBW

You are almost correct.  2(CS)+ID = OD   
2(2.5) + 11 = 16mm in this case 

Oh yeah, silly me. 

[PeWe]

One more thing that most likely is the bandit on oil weeping CB750 K6 setups. Crank case breather
Crank case breather is connected to oil tank via a 1/2" hose, oil tank itself is sealed, no breather. Honda made a mistake here. This will cause oil weeping engine, more cc and rpms more it will weep/leak.

I found out after over 30 years! I have blamed versions of case seal when the biggest cause is no ventilation of the crank case. I trusted the Honda design. Even cars will run as crap with crank case breather problems.

I'll cut the hose between crank case spigot and oil tank, connect with a T-pipe where I'll add another 1/2"  hose going upwards and connect with the breather hose from valve cover. Cut that hose too and add a second t-pipe. Top breather hose from valve cover will still end up beside the exhaust as before.

Hondaman recommend to route that hose to the front drive sprocket to lubricate with the oil drops coming here. The hose must be slimmer where it enters the cover opening.
http://forums.sohc4.net/index.php/topic,147504.msg1680491.html#msg1680491

Edit: My K6 has not the later breather as K7 has and shown beside the airbox. Also shown in Hondamans post above.
https://www.cmsnl.com/honda-cb750k7-four-european-direct-sales_model14391/partslist/F15.html#results

[Scott S]

 Since this one is referred to so often and I go back to it myself, I'm setting it as a sticky. If anyone does a top end, can you take pics and add them to this thread, since Photobucket is holding the pics hostage?

[Niels Bull]

how do you view these pictures??

[HondaMan]

No 8 O-rings on are listed as being 11 x 2.5mm.  Can anyone confirm if 11mm is the inside or outside diameter?  Buna or Viton?

Just one addition: all modern head gaskets are thicker than the OEM gasket upon with the 2.5 mm thickness was established. The modern gaskets are 1.0mm thick (some are even more) where the OEM version was 0.8mm thick, and you need to use an O-ring that is THICKER BY THAT AMOUNT. I use the Parker #01-111 that is listed as 2.62x10.77mm size, but is usually thicker than that, to seal the oil passages between the cylinders and head, AFTER having the cylinder top surface decked 0.010" during boring (which also ensures it is flat) - the head gets decked up to that amount, also.

I have a LOT of these O-rings: if you need a pair, I will send them to you for a donation to our website. PM me for details.

[jnymdnyt]

Thank you so much for this very detailed post and thank you as well for everyone that contributed.  You all just saved me a bunch of time doing research.

[PeWe]

O-ring size: Usually inner diameter x cross section (thickness)
11 x 2.5 has outer diameter 16mm.

So when change to a thicker, inner dia must be smaller to not increase outer dia too much so it still fits. Here inside the gasket holes.

Same with oil feed o-rings. The inner dia can not be too small either so it block the oil feed when compressed.
Here just a few 0.1mm to compensate for thicker gasket.

I used 8 THICK o-rings with late CB750 head gasket and early cyl/head. I had to re-torque the head 3 times until it stopped compressing, nuts moved after 24 hours!!
I used thinner viton O-rings next time (changed head), something like Hondaman recommend. Re-torqued once after 24 hours was enough. (I tested once more)

[ADW]

Here's my experience and suggestion(s) on my 350F from summer of 2019. Reference to gasket sets with taller O-rings and etc. included.

http://forums.sohc4.net/index.php/topic,179085.msg2077683.html#msg2077683