Dirko HT Red is not fuel safe...

[Vintage Engine Repairs]

Hi,

Since running out of my last tube of Dirko HT Red, I have been researching.

I’m stumped... So many of us use Dirko HT Red yet it’s not fuel resistant. Why did stihl recommend this for so long when it clearly says nothing about fuel resistance in the material data sheet and their online charts (any parts that come into contact with fuel for Dirko HT aren’t ticked)

Has anyone here used Dirko and had
leaks / failures that weren’t attributed to poor application?

Out of interest I’m going to submerge Dirko in both gasoline and Motomix, weigh it before and after and see if it has any affect after 24 hours, a week and 4 weeks, see if pulling it apart is easier than the control too. I’ll keep a few strips for control. I’ll let it set up for 24 hours and section it up into short strips.

No need to talk about Yamahabond, hondabond, threebond 1104 or Loctite 518... This is for Dirko alone.

 

[MacAttack]

What is "Curil T"? It seems to be what they recommend for fuel resistance.
TONS of guys here use Dirko Red from what I've read.

 

[CausticUC]

Not sure I agree with your interpretation, it clearly says its suitable for motorcycle and racing. It also lists intakes but not carburetors.

If I were to guess it may be a vibration/shear issue or a material change compatibility issue (steel to aluminum, alloy to plastic, etc).

It should also be noted that this is their own "application" chart. This means if they have a product that performs slightly better in a category it would be selected over another.

You really should refer to the MSDS or SDS to see why rather than a marketing tool.

 

[Vintage Engine Repairs]

Not sure I agree with your interpretation, it clearly says its suitable for motorcycle and racing. It also lists intakes but not carburetors.

If I were to guess it may be a vibration/shear issue or a material change compatibility issue (steel to aluminum, alloy to plastic, etc).

It should also be noted that this is their own "application" chart. This means if they have a product that performs slightly better in a category it would be selected over another.

You really should refer to the MSDS or SDS to see why rather than a marketing tool.

I politely disagree about it being an interpretation issue, it clearly doesn’t state anywhere on any documentation they offer that it’s ok to use in any area that has direct contact with fuel. If a product is fuel safe, they state it clearly on the packaging, MDS and on their website.

They clearly state on their MDS that curilT is fuel safe though -


Note possibly applications above^^ now see Dirko HT Red:


Hence the confusion. Not saying you’re wrong, but just because they state it’s ok on racing etc, has no correlation as to if it’s fuel safe etc.

I’ll try and contact tomorrow Elring too.

 

[CausticUC]

MSDS suggests thermal decomposition is the issue, which is odd as the SDS says -60 to +280 and brief +315C.

Will be interesting to see what they say. Perhaps it is an ethanol related issue? That would also make sense for some of the applications.View attachment MSDS_Dirko_HT_2011.pdf

 

[Deleted member 117362]

Just use Motoseal.

 

[Vintage Engine Repairs]

MSDS suggests thermal decomposition is the issue, which is odd as the SDS says -60 to +280 and brief +315C.

Will be interesting to see what they say. Perhaps it is an ethanol related issue? That would also make sense for some of the applications.View attachment 857452

Interesting stuff! You could be quite right. I have emailed a technician at Elring, I’ll report back when he does to me.

 

[Vintage Engine Repairs]

 

[SteveSr]

I think that part of the issue is that to seal clam shells you need a gap filling sealer which some of the other mentioned alternatives are not. Also to seal the surfaces does not need to be strong. it just needs to seal. Also in the application the material is in compression and not tension. Next consider that product is only exposed to fuel vapors and not liquid fuel. If it is doing its job it is not even getting exposed to fuel vapors. I suspect that Stihl's selection of Dirko HT was a tradeoff of needs and characteristics... like a lot of things in life!

 

[heimannm]

I have been using Dirko HT for 2 or 3 years and not one failure. This includes any number of clamshell type saws including dozens of 10 Series McCulloch saws and not one problem of any kind so far. Dirko HT has been used on saws for quite some time and is the recommended product by/for Stihl saws. If there were any problems I am sure we would all be made aware of it.

Mark

 

[Justsaws]

Cured Dirko HT will break down inside a 2 cycle crankcase if excessive goobers are present. It basically becomes pliable and forms an emulsion that will plug up a spark arresting screen. Keep pulling it over and it will form a bubble and pop. However, only the extra boogers were affected, the sealed parts were still sealed. Basically all the extra squeezings washed off.

Without the spark arrestor it just exits the exhaust.

 

[Vintage Engine Repairs]

I think that part of the issue is that to seal clam shells you need a gap filling sealer which some of the other mentioned alternatives are not. Also to seal the surfaces does not need to be strong. it just needs to seal. Also in the application the material is in compression and not tension. Next consider that product is only exposed to fuel vapors and not liquid fuel. If it is doing its job it is not even getting exposed to fuel vapors. I suspect that Stihl's selection of Dirko HT was a tradeoff of needs and characteristics... like a lot of things in life!

Thanks Steve, lots of very valid points. I wonder, does it really matter then if we just use cheap RTV that’s not fuel safe? Ultimately Dirko is exactly that (just not cheap). The point of gap filling is very true, Permatex very clearly say motoseal is not to be used in place of a gasket.

 

[Vintage Engine Repairs]

Cured Dirko HT will break down inside a 2 cycle crankcase if excessive goobers are present. It basically becomes pliable and forms an emulsion that will plug up a spark arresting screen. Keep pulling it over and it will form a bubble and pop. However, only the extra boogers were affected, the sealed parts were still sealed. Basically all the extra squeezings washed off.

Without the spark arrestor it just exits the exhaust.

Do you know if this happens to other sealants? Ones that state specifically that they are fuel safe?

 

[Vintage Engine Repairs]

I have been using Dirko HT for 2 or 3 years and not one failure. This includes any number of clamshell type saws including dozens of 10 Series McCulloch saws and not one problem of any kind so far. Dirko HT has been used on saws for quite some time and is the recommended product by/for Stihl saws. If there were any problems I am sure we would all be made aware of it.

Mark

I agree, I have used it on all my rebuilds (though most notably oil seals because they are pro saws). This doesn’t mean that it’s fuel safe though hence the reason for the thread.

 

[CausticUC]

I didnt think this thread was supposed to go this way ... myself I use a different product, but I was curious as I do adhesives evaluations for saftey and suitability at my own work when needed.

 

[Vintage Engine Repairs]

I didnt think this thread was supposed to go this way ... myself I use a different product, but I was curious as I do adhesives evaluations for saftey and suitability at my own work when needed.

Annoyingly I just brought 2 tubes of Dirko before this thread Going to sell them and go to motoseal

 

[CausticUC]

Annoyingly I just brought 2 tubes of Dirko before this thread Going to sell them and go to motoseal

You figure it works better than permatex aviation no 3?

I use that one 8/10 times, the other two it is specialized stuff spec'd for Japanese motorsports engines. Then again I am rarely trying to fill a gap.

 

[Vintage Engine Repairs]

You figure it works better than permatex aviation no 3?

I use that one 8/10 times, the other two it is specialized stuff spec'd for Japanese motorsports engines. Then again I am rarely trying to fill a gap.

I have permatex no 3. I’m not yet convinced it’s a good substitute for a proper sealant. I think it works to fill very very tiny scratches in mating surfaces where a gasket is present but that’s about it.

I put some on a copper head gaskit on my model hit and miss engine and it blew right past it / the sleeve step and also on my 07 chainsaw that has a leaking cylinder gasket. It took out most of the leaking, but not all.

It seems Dirko Ht Red is simply just an RTV silicone. It doesn’t have any fuel resistant properties and as you mentioned (or was it someone else) it can fill gaps that other adhesives can’t, that doesn’t make it the right product for the job or best adhesive, just because stihl recommend it. It means it will work, be it at a compromise - it’s just an option of what is available for a specific task, stihl ran with it and now everyone else has.

 

[CausticUC]

I have permatex no 3. I’m not yet convinced it’s a good substitute for a proper sealant. I think it works to fill very very tiny scratches in mating surfaces where a gasket is present but that’s about it.

I put some on a copper head gaskit on my model hit and miss engine and it blew right past it / the sleeve step and also on my 07 chainsaw that has a leaking cylinder gasket. It took out most of the leaking, but not all.

That could be, I do not use it with gaskets. I just it to replace gaskets that are NLA or that i can not cut.

 

[Vintage Engine Repairs]

The two time’s I used it with gaskets it failed, I’m surprised that if it failed with gaskets it would hold without, but clearly you have had success.