Author Topic: Sealant on 750 head gasket or not ? (Read 2979 times)

754 · « **on:** August 08, 2017, 05:41:06 PM »

Using a fiber gasket from a Vesrah kit. Should a run dry, or thin smear silicone ?
Head and cylinder have just been cleaned up not machined.

BPellerine · « **Reply #1 on:** August 08, 2017, 05:54:54 PM »

I have never used silicone on a headgasket frank,I have used coppercoat before,worked ok,a little harder to get off later though.bill

Stev-o · « **Reply #2 on:** August 08, 2017, 06:09:03 PM »

No silicone, ever! (Except on the bathtub).

I also use copper spray, but that is on the Kawasaki with a copper gasket.

scottly · « **Reply #3 on:** August 08, 2017, 06:36:27 PM »

seanbarney41 · « **Reply #4 on:** August 08, 2017, 06:44:39 PM »

Copper spray worked great for me...I would not use a Vesrah gasket without it.

disco · « **Reply #5 on:** August 08, 2017, 08:38:38 PM »

Dry & no problems at all.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #6 on:** August 08, 2017, 08:53:36 PM »

HondaMan · « **Reply #7 on:** August 08, 2017, 09:26:51 PM »

I use mostly Vesrah head gaskets, They need 2 things:
1. Most important: use a thicker-than-normal O-ring on the 2 oil journals at the center rear of the cylinders. ALL of today's head gaskets are thicker than Honda's were, so the old spec of 2.4x12mm O-ring at that site is too thin, and most of the leaks I fix are caused right there. If you can't find the 2.62 x 10.77 O-rings (aka 7/64" x 27/64") at your local Ace Hardware, PM me for a pair, you need them.
2. Smear a LIGHT coating of non-hardening Permatex#2 or Hondbond #4 around this same site. If the engine is the post-K2 variety with the 8 rubber dowels (and steel center dowels) then consider smearing an even thinner coat along the front edge holes. Also, if your cylinders DO NOT have these dowels, make sure the head gasket has the small holes at those 8 sites: if it has the big holes you also need 8 of the 2x11 O-rings, one in each hole, to prevent weeps (I have those, too...). And, vice-versa: if your head has the 8 rubber dowels and the head gasket holes for them are not 14mm size, you need to punch out the holes, or get the other head gasket (I have THOSE, too...).

754 · « **Reply #8 on:** August 08, 2017, 09:56:01 PM »

I am running a 72 cylinder with a 75 ish head.
I have a vesrah, Ibco, and maybe Cometic gaskets, so I have choices.
Either way it goes together tomorrow or next day.
I measured the depth of tge puck hole, there was about 20 thou difference across the head.

scottly · « **Reply #9 on:** August 08, 2017, 10:16:29 PM »

Frank, the TRW pistons are known to have valve clearance issues on the exhaust side.

754 · « **Reply #10 on:** August 08, 2017, 10:21:23 PM »

Really that would throw a wrench in the plan!
The 315 cam has about .375 lift.. i got an Andrews A kicking around that should fit.
I was going to semi tight the head nuts then lift the rocker with a dial indicator on the valve collar.
Wish I had a extra week.

scottly · « **Reply #11 on:** August 08, 2017, 10:24:15 PM »

Notice the crescent shaped indentation at 6:15, where the valve pounded into the piston. This was with a cam with only .312" lift.

754 · « **Reply #12 on:** August 08, 2017, 10:38:39 PM »

Here is the piston,bad pic.
Looks like if you measure of the sharp corner the cutout would be about 90- 100 thou deep.
Problem is, I dont know deck height.
Maybe I got to dig out that A grind.

scottly · « **Reply #13 on:** August 08, 2017, 10:47:13 PM »

My pistons are 65mm, aren't yours 61?
When I cut the reliefs, I wasn't very precise. I basically removed the witness marks, plus a little bit more...

754 · « **Reply #14 on:** August 08, 2017, 10:58:36 PM »

Mine are 61 mm. I WONDER WHY they had the trench on the cutouts.
A grind had .345 and .350 lift. The 315 says .365, but my cam card may have said .375
Hmmmm

scottly · « **Reply #15 on:** August 08, 2017, 11:13:31 PM »

Do you mean the notches in the OD of the crown, at 12:00 and 6:00 in my pic? They seem to be a signature of TRW pistons. My best guess is that they were used to index the forged slug before final machining?

Jerry Rxman Griffin aka MuthaF'er · « **Reply #16 on:** August 09, 2017, 12:00:50 PM »

Surely you are bound to have a spare set of stock pistons sitting around? Are those 12.5:1? Big head.

754 · « **Reply #17 on:** August 09, 2017, 01:07:36 PM »

10.5 to 1 .oo4 clearance, stovk would rattle.
I can always go stock cam, not how it would be with high compression.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #18 on:** August 09, 2017, 06:05:25 PM »

Frank, those domes sure look a lot taller than all the alleged 10:5:1 I've seen??

Get er dun! Godzilla wants to see who is most frightening in person!

754 · « **Reply #19 on:** August 09, 2017, 07:24:33 PM »

Well Jerry it's back to stock pistons. Top chrome ring was a bit tight in the TRW,s.
One stock set of used are actually pretty tight in the bores. Needed lots of cleaning.
Running out if things to surprise me pretty soon.

scottly · « **Reply #20 on:** August 09, 2017, 07:41:48 PM »

What about the F motor you just picked up? When are you planning on leaving?
Here are a couple of pics of 10.5:1 TRW pistons jaguar posted a while back, which was how I figured out that I had TRWs in my engine.

754 · « **Reply #21 on:** August 09, 2017, 08:59:46 PM »

I am trying to avoid engine swap for A few reasons.
After all, just a top end right, should be easy ..right.?
Got stock pistons cleaned up ready to go but got a slightly oval sleeve spigot, must have got bumped or dropped.
So I either bump or press it, or hone the spigot part. .. .003 sideways, about .0012 the other I would be happy if I can get it to . 002....... without cracking it. No shortage of frustration on my plate.

HondaMan · « **Reply #22 on:** August 09, 2017, 09:38:39 PM »

Quote from: 754 on August 09, 2017, 08:59:46 PM

I am trying to avoid engine swap for A few reasons.
After all, just a top end right, should be easy ..right.?
Got stock pistons cleaned up ready to go but got a slightly oval sleeve spigot, must have got bumped or dropped.
So I either bump or press it, or hone the spigot part. .. .003 sideways, about .0012 the other I would be happy if I can get it to . 002....... without cracking it. No shortage of frustration on my plate.

Do you mean on the head, inlet spigot? The hose will usually seal those OK.

754 · « **Reply #23 on:** August 09, 2017, 09:47:12 PM »

No the cylinder sleeve end one. The forged pistons were a bit smaller and fit., but with the stock piston , I got 1/2 thou or less on spigot of the sleeve , it's oval.
I can't remember how forcthe pistons go down, also have not done a motor in ages.

scottly · « **Reply #24 on:** August 09, 2017, 09:54:16 PM »

Why not just swap the motor, Frank? Geeze, between busted cooling fins, the rod damage, and now the messed up sleeve, that motor has a hex on it!

I'm going to be VERY disappointed if you don't make it to Delores...

BTW, I don't care how you get there.

754 · « **Reply #25 on:** August 09, 2017, 10:24:18 PM »

Two problems, I will have a hard time lifting it in no time to make a C frame.
I have a 20 year old sons by the time he gets to helpingm we will have frost on the ground.
Second, I have no idea of what is done to the the spare motor, it appears to be rebuilt and fresh,
But this Punk does not feel lucky...... but I just don't know.
Then there is top end refresh, it really should only take a few days. Right ?

scottly · « **Reply #26 on:** August 09, 2017, 10:36:05 PM »

Quote from: 754 on August 09, 2017, 10:24:18 PM

Then there is top end refresh, it really should only take a few days. Right ?

If it was that easy, it would already be done.

Stev-o · « **Reply #27 on:** August 10, 2017, 06:25:42 AM »

Time is not on your side.
Frank should be off the forum until motor is running!

markreimer · « **Reply #28 on:** August 10, 2017, 01:29:24 PM »

Done three top end's on CB750's, all with a dry head gasket. I used a Cycle-X kit. I used Hondabond on the base gasket along the lower front edge, and on the pucks under the cam towers of course. Everything else went on totally dry. The only time I've had a leak was along the valve cover, once.

RAFster122s · « **Reply #29 on:** August 10, 2017, 02:11:45 PM »

Sounds like that sleeve to lead to piston wear or worse...I would think about changing that sleeve. I agree with Scott, go with different motor. Can spare motor be started out of a bike to see how it runs? How difficult and how much time to test run it?

Do you have a cradle to bolt a motor to a motor stand or something capable of keeping it upright while running?

It might be worth a risk if pulling oan to inspect from below looks good and nothing is out of place on the top end pulling the cover to take a peak at the rockers and valve ends and the cam. That doesn't take more than 90 minutes if everything is laid out and at hand. Take plenty of pics in case you want to review it again later.

Spare motor has good compression and runs well, then go for it. Bribe son with new xbox game if he is into that or a pizza or two... something that motivates him to help.

Good luck!

David

tlbranth · « **Reply #30 on:** August 10, 2017, 06:16:51 PM »

Frankie. Get that mofo running. No excuses - we have beer to consume, untrue stories to tell......

754 · « **Reply #31 on:** August 10, 2017, 07:42:13 PM »

Head is on, torque it tonight, stock cam going in tommorow, Might be Running Friday night .

scottly · « **Reply #32 on:** August 10, 2017, 07:50:18 PM »

If it isn't running and ready to go by tomorrow night, throw it in the back of a truck, and we'll work on it in Delores.

754 · « **Reply #33 on:** August 10, 2017, 08:13:51 PM »

Quick Q .. the 6 6 millimeter bolt from head to cylinder, is it 6 to 8 ft lbs torque ?

scottly · « **Reply #34 on:** August 10, 2017, 08:33:42 PM »

6 to 8 ft lbs sounds about right, but don't go over 8.

PeWe · « **Reply #35 on:** August 11, 2017, 03:08:21 AM »

I tighten all M6 with 10Nm (7,37 ft lbs)

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Author Topic: Sealant on 750 head gasket or not ? (Read 2979 times)