Couple of Q's: Cylinder head cover gaskets, helicoils

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rob
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Couple of Q's: Cylinder head cover gaskets, helicoils

Postby rob » Wed May 17, 2006 12:42 am

Hey everyone,

Just took the cylinder head cover off on an 81 CB650 this afternoon. It looks as if the PO was really liberal with the gasket sealant as it was very where. My CB650C has the sealant applied such that the valve cover gaskets are stuck to the valve covers, whereas this one the gaskets were glued to the engine. Is there a correct side for the gasket sealant to be applied on? Or does it not matter?

The bike is leaking oil into the #1 spark plug hole from the cylinder head cover. The cylinder head cover gasket was in kinda rough shape, and was covered in a lot of gasket sealant, so I will probably replace it. However, the cylinder head cover gasket seems like it is more of an O-ring than a gasket: does it require gasket sealant? Or is it better to just clean both surfaces and use a pressure fit?

One of the cylinder head cover bolts appears to have been helicoiled: the threads on the bolt have some metal wrapped in them all the way along its length, and I t rotates freely, and came out when I unbolted the head cover. I've never dealt with helicoils before, I take it I will need to re-do the helicoil in order to bolt it down again?

Thanks,

Rob
'81 CB650 Custom

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Volker_P
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Re: Couple of Q's: Cylinder head cover gaskets, helicoils

Postby Volker_P » Wed May 17, 2006 2:02 am

Hi,
the three valve covers have rubber gaskets, they should not require any additional sealant. If they do, probably the rubber part below the wide washers on the bolts is worn. The bolts are turned in up to the end of the thread, this rubber part provides an elastic pressure on the covers. It is more effective to insert a thin washer above the wide washers to restore tightness instead of excessive usage of sealant here.

The large O-ring just has to be clean and so do its opposite surfaces. If surfaces are allright and everything is really clean, it should get tight. Otherwise the head cover might be bent. If the O-ring surface is too bad, you can just buy a 3.5 x 1240mm rubber rope at a workshop and glue it together at both endings. I did this after I gave back the original Honda part because it showed "pickles" all over the gasket! :x

Be careful opening and tightening the bolts. Use several steps and urgently a small torque wrench. 10Nm should be enough to get tight, mine e.g. did with 8Nm.
Depending on how they were inserted, helicoilds can be allright or quit annoying. If the spiral is still intact, you could try to screw it in together with the bolt and some locktite in the thread in the cylinder head. Clean this thread from oil before. If you are lucky, it does not break and gets fixed again. You could also try to screw in a bolt with a full thread with the helicoil and locktite on both sides of it. Once stuck, it stays fixed from then on and you have to use a nut instead of a bolt at this place. Depending on the position, you may not be able to remove the cylinder head cover with the engine in the frame any more.

Good luck!

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Chris
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Postby Chris » Wed May 17, 2006 9:57 am

Regarding the liberal use of gasket sealant... that's a big no no with car engines and I imagine that would go for these bikes as well. The reason being that the sealant will break off in little chunks inside the engine and block your oil passages and pickup screen causing oil problems and subsequent engine damage :shock: If you have to use it, be very careful to use only what you need.
1980 CB650c

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Postby Guest » Wed May 17, 2006 10:15 am

Thanks for the replies. There is gasket sealant all over the head cover.. on valve springs for example.

The coil still looks fairly intact, a little bit has broken off the end. I will try inserting with locktite when I rebuild the head, but only on the cylinder sidse. The idea of not getting it apart again with the engine in the frame doesn't appeal to me. The other option may be to re-tap the thread a little larger. Could this drop metal filings into the cylinder?

Thanks again,

Rob

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Ibsen
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Postby Ibsen » Wed May 17, 2006 11:01 am

I agree about not using gasket sealant, especially silcone . If it brakes loose from the inside it can easily clogg up the oilways. And the best would be to replace the rubber gaskets. Over time they will be permanently compressed, and the rubber will harden, so they will fail to seal.

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DammitDan
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Postby DammitDan » Mon May 22, 2006 11:17 pm

YES re-tapping will create bajillions of little aluminum shards that will go everywhere if you're not careful. I had to put a helicoil in for one of my headbolts, and boy did that create a lot of little metal shavings. Thank God I thought to duct tape every hole I could find.

If it's for the cylinder head bolts, I would re-tap. If it's for the cylinder cover bolts, I would loktite. The cylinder head cover (with the rocker arms and tappets) only requires 7-9 ft lbs of torque to get it in place, and as long as you're careful you should be able to just thread it back into place. However, consider getting a new helicoil for the job... They cost like $0.30 apiece and they're super simple to install (you can do it with a slightly altered bolt or even a flathead screwdriver if you're careful.) They're not supposed to come out like yours did... Once they seat inside the tapped threads, they lock in place when you screw in the new bolt. I've never had one come out without sustaining some serious damage first.


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