Topic: k2 base gasket install, warped head?

[persson-johan@hotmail.com]

Im about to put the cylinder and head on my engine. Ive seen a few different variations on how many o rings that are used between the case to cylinder. When looking at cmsln it looks like i only need 2 for the k2?

Ive seen some pictures of builds that also uses some small o rings tight around the studs. Are they for later models or something that could/should be used on the k2 also?

Best regards
Johan

[Davez134]

Only the 2 o-rings on K2. On the later heads, it is obvious where those others you're talking about would go, cant install on K2 cylinders/head.

Assuming everything is original to your motor, cases and jugs should look like this, with 2 o-rings going on top surfaces of each where indentations are, toward rear.

[persson-johan@hotmail.com]

Ok! Yes it looks like that. Thanks for a quick answer

/Johan

[persson-johan@hotmail.com]

Seems like vesrah only sends 2 o-rings.. (orange)

Hope ill find the right size before wrenching on sunday!

[Kevin D]

Did you find the big ones for the cylinders? 61.8 x 2mm

http://www.cmsnl.com/honda-cb750k2-four-usa_model14362/partslist/E05.html#results

[persson-johan@hotmail.com]

Yep! Those I got! Phew..

[HondaMan]

Always place the base gasket on the block, then drop the O-rings from your gasket kit onto those studs, then measure how much they stick up above the base gasket. We have recently seen lots of O-rings coming in kits that are too thin in cross-section, which soon causes leaks. The O-ring here is 2.4mm in thickness, and should stand up 0.1mm above the gasket, for best results. If yours is too thin, drop me a PM, as I have some thicker ones (2.62mm), too.

This same rule applies at the head gasket. Many head gaskets today are too thick, or, again, the O-rings in the kits are too thin. Honda's head gasket was 1.00 to 1.04mm thick, compressing to .94 to 1.00mm thick at 15.2 ft-lbs of torque. The typical Vesrah (slippery) head gaskets are 1.10mm thick, and hardly compress at all, even at 18 ft-lbs. This has led to many head gasket leaks, and was the reason I switched to these 2.62mm thick O-rings there, also to stop the leaks.

There are some head gaskets out there which start at 0.92mm and compress to 0.88-0.90mm when installed: these will work OK with the 2.4mm thick O-rings supplied in most kits. The ones from Dik come to mind, sbutcheck your head gasket to be sure.

[persson-johan@hotmail.com]

I have some 2.62 mm o rings. Maby I should use them for the head? Is it better to also use them for the cylinder or might they be to thick?

Thanks for the reply's! Always get some good answers here

[HondaMan]

I have some 2.62 mm o rings. Maby I should use them for the head? Is it better to also use them for the cylinder or might they be to thick?

Thanks for the reply's! Always get some good answers here

I use them for most heads, unless it is some special thinner head gasket, or a genuine Honda head gasket made correctly. On the cylinders, measure first: if the O-rings there are too thick they might squish the opening partly closed and the oil may be restricted when the engine is cold. That's why I always measure the hole depth and O-ring "rise" above the gasket there, first.

[persson-johan@hotmail.com]

I was just about to install the cylinder and head today when i noticed this!:




Looks like its warped right? Is it "normal" to have the head like this? I guess not.. hehe. The light you see is the gap between the head and cylinder in the middle by the cam tunnel.

Good thing i saw it before installing! I smeared some gascacinch on the base gasket that will now cure until i put it on. Will this be alright or should i toss it?

/Johan

[Trad]

It looks like the cylinder was surfaced, did you do the head? I'm guessing not. Take straight edge and check the head and cylinder to confirm which one is warped a bit. No biggie, you should be able to get that little bit milled flat no problem.

[persson-johan@hotmail.com]

Neither is surfaced. The picture further up isnt mine yes i guess i will need to take some of to get it straight again!

[HondaMan]

Many, many of these heads warp a bit when removed from their engines, so I usually have them milled flat when rebuilding. Sometimes I have the cylinders done, too, but they seem to warp far less, and less often.

[persson-johan@hotmail.com]

Ok! I'll have them check the cylinder also. How much can I take off without messing up the clearance and timing?

[bytio]

Check that you have correct dowels on cylinder head  to cylinder join, if too long you will get that gap

[persson-johan@hotmail.com]

The gap appears without the dowels in place.

[mystic_1]

Have you checked with a straight edge to see if there's a high spot localized around the central 6mm threaded holes?  You can sometimes get that if the person who assembled the engine last torqued them down pretty well. 

If it turns out to be this then it can be fixed with a hone and/or a countersink bit.

mystic_1

[persson-johan@hotmail.com]

Good tip! Doesnt seem to be the case, unfortunately! The head sits real flat in the corners but you start to see light going closer into center. If the 6mm holes were the problem it should sit on top of that and "wiggle". Its just a small small gap so i dont think i will have to take off much at all.

Anyone know much you can you take off before timing and clearance becomes an issue?

[persson-johan@hotmail.com]

Found a guy in the neighbourhood who did the head for me A real legend in the racing world here in Sweden, right around the corner! Sweet.

He only had to take off about 0.15 mm (6 thousands of an inch) to get it straight. I guess this wont be a problem with the cam timing? Or clearance?

He really did a nice job!

[calj737]

You also need to reduce the height of the locating dowels and adjust the depth for the o-rings as a result. Proper thickness gasket too.

[HondaMan]

Found a guy in the neighbourhood who did the head for me A real legend in the racing world here in Sweden, right around the corner! Sweet.

He only had to take off about 0.15 mm (6 thousands of an inch) to get it straight. I guess this wont be a problem with the cam timing? Or clearance?

He really did a nice job!

That will be fine: you can take up to 1.5mm off the heads and things work out well. This is more commonly done on the F2/3 engines because of their large combustion chambers and (up until now, see my post about new pistons!) lack of pistons to restore the compression during a rebuild.

Usually, the dowels Calj is referring to above have 2mm extra clearance in the head. But there always is the 'Monday morning tech' situation where a hungover worker may have forgotten to set his depth gage before boring them!

[persson-johan@hotmail.com]

Great! I have already had to grind the dowels. I hade 2 pair of the tall ones.

Waiting for 3 head stud washers and then its time to button it up!

Thanks for all the help! Really appreciate the answers!

[PeWe]

Talking about o-rings.
The 4 o-rings under the cam towers are usually very thin too. I had o-rings from a Yamiya gasket kit as well as cmsnl. I did not trust neither of them when they had not much stick-out over the head in my K6 engine, surface mating the cam tower oil holes.  I found other thicker that sealed well. Same with  round rubber pucks under the cam tower. I used some sealer under them when they could have been thicker.

Same with the 2 o-rings cylinder-head

[HondaMan]

Talking about o-rings.
The 4 o-rings under the cam towers are usually very thin too. I had o-rings from a Yamiya gasket kit as well as cmsnl. I did not trust neither of them when they had not much stick-out over the head in my K6 engine, surface mating the cam tower oil holes.  I found other thicker that sealed well. Same with  round rubber pucks under the cam tower. I used some sealer under them when they could have been thicker.

Same with the 2 o-rings cylinder-head

You're right (as usual) PeWe: I've seen those O-rings, too. They are coming as 1.8x5.8 (or sometimes 1.8 x 5.9) size in some kits, where Honda declares they must be at least 1.9x5.9 size. I use 2x6 instead, which allows both a tighter seal (for synthetic oils, if used) and fixes the occasional too-deep pocket where the rings sit. These are more widely available, too.

This is a particular help on the countershaft bearing housing, which uses the same size O-ring, as those are often slightly warped and don't seal today like they did 40 years ago. The result there is a smoother-shifting tranny.