rocker box gaskets again

[KeithJ]

Has anyone tried using thin paper gaskets with a thin coating of silicon sealant on both sides?  I've used this technique on other places and will try it on my rebuild.  Essentially, make a thin paper gasket, get some silicon sealant and smear it on "evenly" on both sides by pulling it through finger and thumb, let the silicon dry and then fit it.  Should minimise the silicon sealant getting in to the engine oil ways but fill the gaps with a resilient sealant.  ATB Keith

[KiwiGF]

Ive not tried silicon but do make my own gaskets in 0.8mm "Flexoid" paper, I use Loctite "Master Gasket" and have no leaks. When making the gaskets I make them wider than standard on purpose, so maybe as much as 3 mm sticks out into the inside of the box, and ouside, and I cut the visible paper off the ouside with a knife, as per prior post by dutch.

I dont think the paper would drop off the inside and cause problems....

I use the same technique on the primary case and timing cases, but loctite on the bottom half of the faces (saves mess and money!). Its a bit of an art getting the primary case on without disturbing the loctite. I use 2 old bolts with heads removed as "guides". I make the primary case gasket about 15mm wide, with no "dip" around bolt holes etc so theres a fair bit of paper sticking inside of the case.

Making yr own gaskets is tedious but makes sure you get the full width of paper between mating faces, like the pics in above posts I found some gaskets were pretty much the exact width of the mating faces and because they were not exactly the right shape this resulted in a relatively thin width piece of paper stopping the oil getting out.

[bsa-bill]

you get the full width of paper between mating faces

Spot on KiwiGF. I found this to be the answer also, and yes the silicon thing is good also

[KeithJ]

Ive not tried silicon but do make my own gaskets in 0.8mm "Flexoid" paper, I use Loctite "Master Gasket" and have no leaks. When making the gaskets I make them wider than standard on purpose, so maybe as much as 3 mm sticks out into the inside of the box, and ouside, and I cut the visible paper off the ouside with a knife, as per prior post by dutch.

I dont think the paper would drop off the inside and cause problems....

I use the same technique on the primary case and timing cases, but loctite on the bottom half of the faces (saves mess and money!). Its a bit of an art getting the primary case on without disturbing the loctite. I use 2 old bolts with heads removed as "guides". I make the primary case gasket about 15mm wide, with no "dip" around bolt holes etc so theres a fair bit of paper sticking inside of the case.

Making yr own gaskets is tedious but makes sure you get the full width of paper between mating faces, like the pics in above posts I found some gaskets were pretty much the exact width of the mating faces and because they were not exactly the right shape this resulted in a relatively thin width piece of paper stopping the oil getting out.

Why use gaskets?
The Master Gasket 518 is shown used on its own.

Would the 510 be a better bet as it has a higher max temp although gap fill is not quite as good?

Perhaps it's a colour thing?

Loctite 510
Technical Data

Colour: Pink
Service temperature range: -50°C - +200°C
Tensile shear strength: 5N/mm²
Max. gap: 0.25mm
Fixture time steel: 25 min.
Fixture time aluminium: 45 min.
Strength: Medium
Cure method: Anaerobic
Pack sizes: 10ml, 250ml

Loctite 518
Technical Data

Colour: Red
Service temperature range: -50°C - +150°C
Tensile shear strength: 7.5N/mm²
Max. gap: 0.3mm
Fixture time steel: 25 min.
Fixture time aluminium: 20 min.
Strength: Medium
Cure method: Anaerobic
Pack sizes: 25ml, 50ml, 65ml, 80ml, 300ml

ATB  Keith

[Rocket Racer]

gasket preferences are like choosing oil, everyone has their own golden rules. Our bikes also put up with a variety of treatment and environments.
I was chatting over the weekend to a guy with an oil tight road going A10    . For my race engine I'm happy if I can keep losses down to weaps and the rocker boxes do a lot of work on the swingarm bikes when the engines are worked hard.
Personally on the rocker boxes I doubt I could assemble solely with goo without disturbing it, but I could be wrong and as the rocker box comes off regularly do keep trying alternative options.
I use three bond grey in general, but havent had sucess on my rocker boxes solely with goo only options.
On my road engine i suspect I will do better with oil tightness, but am not going to lose sleep over needing to wipe it down once in a while

[KiwiGF]

Hi KeithJ, I use the Loctite 518 variant. I tried a "no gasket" approach on the primary cases as that gasket is a pain to make and it seemed I would be forever finding reasons to remove the cover but it leaked badly without a gasket so I went back to using the thin gasket approach.

Just a theory but using a gasket effectively means you get 2 thicknesses of gasket goo, so more chances of sealing a gap?

On my primary case I can fit a 10 tho feeler guage between screw holes so there is a fair gap to fill, due to the cases being distorted.

I have tried using thin (ish) gaskets with just grease. then Loctite 518 one side and grease the other so the (thin) gaskets would come off cleanly and could be re-used, but I got leaks, so for me I have to comprehensively clean gaskets faces and use new gaskets and the loctite both sides....every time.

I've not gone as far as using a glass plate and wet and dry paper to flatten gasket surfaces, as I have found what works for me to stop leaks. When rebuilding my engine I did carefully file the cases where needed, around the bolt holes, to remove the "obvious" raised areas, just to reduce the gaps a bit.

At least the Loctite is fairly easy to remove compared to some sealants, and as far as I can tell it does not have the same tendency to clog oil ways as silicon, at least I've never found any on the various gauze filters.

[bikerboy]

Hi guys, the head steady is the obvious problem so what would be the effect if it was not used,cheers
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Not only will it increase vibration but its very likely that the barrel will crack around the skirt, even the thick flange ones can do this if you run without a head steady.

Please dont ask me how I found this out many years ago