Author Topic: 1978 CB750K — Post 836 OIL PRESSURE - not good (Read 248200 times)

SOHC4 Cafe Racer Fan · « **Reply #850 on:** December 08, 2015, 11:29:36 AM »

Quote from: SKTP on December 08, 2015, 10:28:47 AM

Nope...I have thought about it, but I don't think for my height, that it really does anything for me...at this point I just want to get it back together...maybe down the road

I noticed that you had your front calipers off the wheel. Is the rest of the bike now just awaiting the engine -- or is there more work?

SKTP · « **Reply #851 on:** December 08, 2015, 01:17:16 PM »

Front brakes. Maybe front fork emulators. That should be it...

edwardmorris · « **Reply #852 on:** December 08, 2015, 02:15:28 PM »

About the Hondabond, if you're sticking to applying it to the top case, I'd put a thin layer on ALL the colors in your image. When I did this, it just made more sense to put the HB on the lower half and apply a little around the front-center large o-ring/dowel area on the top half just to be safe. Has held up well for a 1000 miles thankfully. Just grab the lower case at the oil filter hole and the oil galleys under the oil pan when putting them together. One thing that got tricky was to get the shift fork to seat right, but its a no-brainer if you have a second set of eyes and hands helping.

SKTP · « **Reply #853 on:** December 20, 2015, 10:09:21 PM »

Cases back together after picking off the HT and re-cleaning everything. I just got them back together with Hondabond #4. My fingers are crossed that I got everything right this time. Had a little trouble getting the cases to mate cleanly (I think the transmission gears to mesh) took a couple goes (even though my no-bond tests went smoothly)...pretty sure I got it smooth, even and thin...third times a charm?

SKTP · « **Reply #854 on:** December 26, 2015, 11:35:46 PM »

Ok...a couple questions:

I'll call Ken at cycle-x tomorrow to be sure, but will these rivits on the MLS gasket get in the way or do they just crush?

Also, I'll search all the manuals tomorrow, but to the four "under the pucks" bolts go in before or after the main stud tightening sequence? And what torque do those smaller guys get? I couldn't easily find it this evening...its 11:34pm here now. I'll update tomorrow....progress is being made!

Restoration Fan · « **Reply #855 on:** December 27, 2015, 06:23:31 AM »

On my K8, we tightened the studs all down to spec. Let it sit overnight and then retightened the next morning. Once that was done, we put the pucks on with a little dab of HondaBond. As to the specs on the smaller 4 inner bolts, just go by the diameter size of the bolt. IIRC, that's 8 foot pounds for that size?

The four under the puck bolts we included in the tightening sequence so they got tightened twice as well.

edwardmorris · « **Reply #856 on:** December 27, 2015, 09:44:15 AM »

The inner bolts are 6mm and don't need more than 90in-lbs. Its often debated whether these need to be torqued down before or after the mains. One school of thought is that these small ones help seat the head first, then you tighten the mains. The other is that you do the mains first, then the inners, which loosens the mains a hair, so you re-torque the mains again. I did the latter without issue, and IINM Dino did the same in one of his vids.

Those rivets stick out and away from the mating surfaces on the MLS. If you have the surfaces milled, then the MLS doesn't require a re-torque after 24h, but no harm in doing it anyway.

SKTP · « **Reply #857 on:** December 27, 2015, 12:19:48 PM »

Torque one just happened. I am now thinking that something is not flat. There's a tiny gap visible through the MLS head gasket on the alternator side....maybe a 24 hour retorque will fix this...but I doubt it...why can nothing be easy?

* UPDATE: I eased off all the stud-nuts and redid the sequence. I'd say I can see a slight hairline of light on either outside edge of the head gasket (if I shine a flashlight behind it)...it's fairly even on both sides...maybe that's just how it is? Or my jugs are high in the middle? First MLS gasket, maybe this is normal?

edwardmorris · « **Reply #858 on:** December 27, 2015, 06:51:31 PM »

I could be wrong but that doesn't sound right to me.

SKTP · « **Reply #859 on:** December 27, 2015, 08:44:40 PM »

The second one without the flashlight was the first attempt....the light is less of a gap

This photo is taken from the from of the engin looking from the front to the back

Cycle-x MLS gasket. APE resurfaced my head. I removed all the knock-pins from the cylnder. It all looks flat....WTF?

?? One step forward, two back...

edwardmorris · « **Reply #860 on:** December 27, 2015, 10:24:59 PM »

Were the Cylinders milled flat too? Or just the head?

SKTP · « **Reply #861 on:** December 27, 2015, 10:35:18 PM »

Yeah that's what I'm thinking too...only the head was resurfaced

hotdog · « **Reply #862 on:** December 28, 2015, 01:30:39 AM »

Dowels aren't too long, holding the head off the cylinder..?

Sent from my HTC_M9u using Tapatalk

SKTP · « **Reply #863 on:** December 28, 2015, 06:47:57 AM »

The dowels are stock and were never removed

madmtnmotors · « **Reply #864 on:** December 28, 2015, 08:27:34 AM »

Quote from: SKTP on December 28, 2015, 06:47:57 AM

The dowels are stock and were never removed

Once the head was milled there is now the possibility that the counterbores in the head are no longer deep enough. The only way to know for sure would be to bust out the caliper and measure the length of the dowels that extend above the cylinders vs. the depth of the counterbores in the head at these locations.

SKTP · « **Reply #865 on:** December 28, 2015, 09:29:55 AM »

That makes sense...I will pull the jugs off for a third time. I hope that's all it is...

Thank you guys

madmtnmotors · « **Reply #866 on:** December 28, 2015, 09:31:05 AM »

Quote from: SKTP on December 28, 2015, 09:29:55 AM

That makes sense...I will pull the jugs off for a third time. I hope that's all it is...

Thank you guys

You would not have to pull the jugs, only the head. While you're at it, maybe lay a straight edge across the cylinders and the head and see if either is less than flat.

SKTP · « **Reply #867 on:** December 28, 2015, 09:38:21 AM »

Hey you're right! That's much better news...

edwardmorris · « **Reply #868 on:** December 28, 2015, 09:55:09 AM »

IINM MLS works best when BOTH surfaces are milled flat. If you can, you may want to consider that as well. Not sure about the K7/K8 but at least in the early K parts fiches, the part number for the dowel pins was incorrect (too long). I had both surfaces milled on mine, but I didn't reuse the old pins. I ordered the correct size (shorter) ones and they worked without any trimming despite both surfaces being milled. That's another option for you (new shorter pins). The part numbers are all noted in Branden's top end thread.

SKTP · « **Reply #869 on:** December 28, 2015, 10:06:38 AM »

It took me 3 night to remove the knock-pins of the studs...those other 2 dowel pics seem locked in there even more...this should be interesting

this is the second time I have rebuilt this engine, but the first time with the resurfaced head and a MLS gasket...I really don't want this thing to leak...last time it leaked from the pucks but the head gasket was fine with just the cycle-X "kit" head gasket...I do want to do it right...but I also do not want to spend more money...if it is just the pin length...I think I'll take my chances with the current jug-surface...or is that a horrible plan?

madmtnmotors · « **Reply #870 on:** December 28, 2015, 10:59:50 AM »

Quote from: SKTP on December 28, 2015, 10:06:38 AM

if it is just the pin length...I think I'll take my chances with the current jug-surface...or is that a horrible plan?

Depends on the results of the straight edge check for flat. There is an allowable tolerance for being less than flat (should be in the service manual) but I can't remember what that tolerance is, maybe .002" or .003"? The location of any deviation could also influence the decision (i.e. if the deviation were at the very edge as opposed to right next to the oil passages or fire ring...).

SKTP · « **Reply #871 on:** December 28, 2015, 08:53:15 PM »

Well I think it's those rivets on the MLS gasket. I think I will snip the two on the back side off...you can see how it tried to squish...maybe other heads don't have that half circle? If the rivet was anywhere but there, I think it would work just fine. This is my working theory for now...those holes for the pins are very deep...can't be from the resurfacing...

firebane · « **Reply #872 on:** December 28, 2015, 09:01:59 PM »

I'm by no means an expert when it comes to motorcycle engines but I would say that gasket is not the correct one for that application.

edwardmorris · « **Reply #873 on:** December 28, 2015, 09:02:10 PM »

That's very interesting, perhaps you should mention it to Kenny? On the early head, they clear the mating surfaces fully, but from your pix, the later heads are definitely getting fouled by them.

firebane · « **Reply #874 on:** December 28, 2015, 10:24:57 PM »

not sure of the year but this is a cb750 head which as mentioned does not have the rounded parts. Which leads me back to the wrong gasket in use?

http://farm5.static.flickr.com/4044/4469246642_38b325f9e7_o.jpg

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Author Topic: 1978 CB750K — Post 836 OIL PRESSURE - not good (Read 248200 times)