Log in
Search
Latest topics
» A prototype Cox Reed-valve marine engineby roddie Yesterday at 11:51 pm
» My Cox .049 Marine inboard engine
by 1/2A Nut Yesterday at 11:41 pm
» Here we go again... another Lawn-Boy
by Cribbs74 Yesterday at 10:52 pm
» Jim Walker Firebaby
by rsv1cox Yesterday at 7:26 pm
» Roddie-Rigger.. a 2005 original design
by roddie Yesterday at 7:04 pm
» music vids.. some of your favorites
by HalfaDave Yesterday at 6:55 pm
» Norvel Needle Needed
by Greenman38633 Yesterday at 5:36 pm
» World's largest weathervane
by Cox International Yesterday at 3:38 pm
» Help Pee Wee tank cap .020
by rdw777 Yesterday at 1:30 pm
» **VOTE-ON-THE-NEXT-COX-ENGINE-OF-THE-MONTH** (May 2024)
by GallopingGhostler Yesterday at 11:34 am
» Revivng Some Childhood Classics
by getback Yesterday at 8:21 am
» Jim Walkers FireBee - This is going to be fun
by rsv1cox Tue May 07, 2024 7:29 am
Cox Engine of The Month
head gaskets
Page 1 of 1
head gaskets
I've read about adding head gaskets for higher nitro. Something like one gasket for 10%, two gaskets for 20% and so on. And Rusty just said something about more gaskets for cold weather and less for warm weather. Is there a standard? I usually run 30% but have never run more than one gasket.
duke.johnson- Diamond Member
- Posts : 1734
Join date : 2012-11-05
Age : 52
Location : Rochester, Washington
Re: head gaskets
The rule of thumb is two shims(gaskets) for 20% nitro and add one for every 10% above that. Below 20% you can use one, but I say play it safe with two. You can blow a glow plug if you use too few. With 25% fuel I still use two, but with 35% I use three. This is with Cox heads. The replacement plugs with the clamp type head that Cox International sells(Merlin plugs and clamp rings) are higher compression than any Cox head and require extra shims, one or two extra. I never run less than three with those.
Cold air is more dense so just a drop in temp raises compression. I don't have any rule of thumb for adding or removing a shim at certain temps. As long as you follow the general nitro rule you should be safe from blowing plugs. In the other thread where you saw me mention temperature, I was using a high compression Merlin drop-in plug. I probably blew that one from cranking it while flooded on a cold day with three shims. Being flooded it put too much pressure on the glow element.
These...
http://coxengines.ca/cox-.049-glow-plug-adapter-extra-cooling.html
and these...
http://coxengines.ca/cox-.049-glow-plug-adapter-insert-style.html
...are the same thing. One just has more fins. They are higher compression than ANY Cox .049 head and require from one to three extra shims. Up to Five depending on how your engine behaves. I really like the three fin clamp ring. The five fin extra cooling one is mostly to look cool.
Cold air is more dense so just a drop in temp raises compression. I don't have any rule of thumb for adding or removing a shim at certain temps. As long as you follow the general nitro rule you should be safe from blowing plugs. In the other thread where you saw me mention temperature, I was using a high compression Merlin drop-in plug. I probably blew that one from cranking it while flooded on a cold day with three shims. Being flooded it put too much pressure on the glow element.
These...
http://coxengines.ca/cox-.049-glow-plug-adapter-extra-cooling.html
and these...
http://coxengines.ca/cox-.049-glow-plug-adapter-insert-style.html
...are the same thing. One just has more fins. They are higher compression than ANY Cox .049 head and require from one to three extra shims. Up to Five depending on how your engine behaves. I really like the three fin clamp ring. The five fin extra cooling one is mostly to look cool.
_________________
Don't Panic!
...and never Ever think about how good you are at something...
while you're doing it!
My Hot Rock & Blues Playlist
...and never Ever think about how good you are at something...
while you're doing it!
My Hot Rock & Blues Playlist
RknRusty- Rest In Peace
- Posts : 10869
Join date : 2011-08-10
Age : 68
Location : South Carolina, USA
Re: head gaskets
Rusty, thanks for the help.
duke.johnson- Diamond Member
- Posts : 1734
Join date : 2012-11-05
Age : 52
Location : Rochester, Washington
Re: head gaskets
Its only the high compression heads that need more gaskets, you are fine running standard Cox heads with one gasket.
Thats most likely what you been running on 30% with one gasket.
Thats most likely what you been running on 30% with one gasket.
crankbndr- Top Poster
- Posts : 3073
Join date : 2011-12-10
Location : Homestead FL
Re: head gaskets
With the one gasket each 10% rule they start more easily
And the glows are less prone to blow.
And the glows are less prone to blow.
John Goddard- Diamond Member
- Posts : 2447
Join date : 2011-11-24
Age : 59
Location : Leyton North East London
Re: head gaskets
crankbndr wrote:Its only the high compression heads that need more gaskets, you are fine running standard Cox heads with one gasket.
Thats most likely what you been running on 30% with one gasket.
Must be, we don't blow head very often. Would I get more RPM's with the high comp. heads? Is it worth the upgrade?
duke.johnson- Diamond Member
- Posts : 1734
Join date : 2012-11-05
Age : 52
Location : Rochester, Washington
Re: head gaskets
You should be able to pick up 7,8,9 hundred RPM using the drop-in plug Rusty linked to, but they will need to be tuned like Rusty said.
crankbndr- Top Poster
- Posts : 3073
Join date : 2011-12-10
Location : Homestead FL
Re: head gaskets
crankbndr wrote:You should be able to pick up 7,8,9 hundred RPM using the drop-in plug Rusty linked to, but they will need to be tuned like Rusty said.
Seem like it would be worth it after the head was bought with the cheaper glow plugs. And by tuning, you mean adding or omitting head gaskets?
duke.johnson- Diamond Member
- Posts : 1734
Join date : 2012-11-05
Age : 52
Location : Rochester, Washington
Re: head gaskets
Here is a Utube vid of a test run I did on my Mouse engine I sent to the tach race last year.
The first run is with a standard Cox head, the second is the Merlin drop-in. It picked up about 1K.
25% nitro, 5/3 prop
https://www.youtube.com/watch?v=eU6xQEkngkI
The first run is with a standard Cox head, the second is the Merlin drop-in. It picked up about 1K.
25% nitro, 5/3 prop
https://www.youtube.com/watch?v=eU6xQEkngkI
crankbndr- Top Poster
- Posts : 3073
Join date : 2011-12-10
Location : Homestead FL
Head gaskets...
Hi Duke,
Long story short...no there is no standard, with the exception that don't use less than one shim.
One of the reasons is because there is no standard prop & fuel. Different props & fuels have different head clearance requirements. Another reason has to do with piston to cylinder fit. A "looser" fit here seems to need less shims.
Changing from a standard Cox head to a TD head almost always results in more power/rpm (up to 1,000 more in some cases).
If you want maximum power, you'll have to burn out a few glowheads experimenting...
If your engine runs just fine with one head shim, I doubt adding more shims will make it run better.
Of course the real 'truth teller' is your tachometer, because it don't lie!
Lastly, some shims "fuse together" after awhile & look like just one when in fact there are two, giving mis-leading results. As well, it's not uncommon to have a replacement shim not seat flat in the cylinder.
Screwing on the glowhead with the thin copper shim scrunched in the threads usually causes a small leak that messes everything up. (happens to me frequently)
SOoo...feel free to play. Coxes are fun that way & sometimes the results are surprising.
Good Luck!
Cheers, Paul
Long story short...no there is no standard, with the exception that don't use less than one shim.
One of the reasons is because there is no standard prop & fuel. Different props & fuels have different head clearance requirements. Another reason has to do with piston to cylinder fit. A "looser" fit here seems to need less shims.
Changing from a standard Cox head to a TD head almost always results in more power/rpm (up to 1,000 more in some cases).
If you want maximum power, you'll have to burn out a few glowheads experimenting...
If your engine runs just fine with one head shim, I doubt adding more shims will make it run better.
Of course the real 'truth teller' is your tachometer, because it don't lie!
Lastly, some shims "fuse together" after awhile & look like just one when in fact there are two, giving mis-leading results. As well, it's not uncommon to have a replacement shim not seat flat in the cylinder.
Screwing on the glowhead with the thin copper shim scrunched in the threads usually causes a small leak that messes everything up. (happens to me frequently)
SOoo...feel free to play. Coxes are fun that way & sometimes the results are surprising.
Good Luck!
Cheers, Paul
duke.johnson wrote:I've read about adding head gaskets for higher nitro. Something like one gasket for 10%, two gaskets for 20% and so on. And Rusty just said something about more gaskets for cold weather and less for warm weather. Is there a standard? I usually run 30% but have never run more than one gasket.
Paulgibeault- Gold Member
- Posts : 259
Join date : 2011-09-24
Location : Leduc, Alberta Canada
Re: head gaskets
I have used zero shims with no nitromethane. Works fine. The aluminum head seats to the steel cylinder just fine.
No. Not recommended.
Phil
No. Not recommended.
Phil
pkrankow- Top Poster
- Posts : 3025
Join date : 2012-10-02
Location : Ohio
Re: head gaskets
I always like it when Paul G. tosses in on one of our topics. I can imagine him sitting back reading all of our follies shaking his head when he finally figures it's time to speak up and save us from ourselves.
I have at least one Cox that I can't turn through TDC with no shims. It may have a stretched rod or something allowing it to contact the head. From the time I was a kid until I went full bore with my hobby a few years ago I had only ever used one shim, and only ever blew one plug. Maybe the old Cox fuel didn't have as much nitro as what I use now. Then one day I blew two back to back in the air on a Black Widow. That's when the RCG folks told me I should always run two. I have done so ever since then.
I have at least one Cox that I can't turn through TDC with no shims. It may have a stretched rod or something allowing it to contact the head. From the time I was a kid until I went full bore with my hobby a few years ago I had only ever used one shim, and only ever blew one plug. Maybe the old Cox fuel didn't have as much nitro as what I use now. Then one day I blew two back to back in the air on a Black Widow. That's when the RCG folks told me I should always run two. I have done so ever since then.
_________________
Don't Panic!
...and never Ever think about how good you are at something...
while you're doing it!
My Hot Rock & Blues Playlist
...and never Ever think about how good you are at something...
while you're doing it!
My Hot Rock & Blues Playlist
RknRusty- Rest In Peace
- Posts : 10869
Join date : 2011-08-10
Age : 68
Location : South Carolina, USA
Re: head gaskets
....back in the day, lol, when i was flying 1/2a pylon a guy (who had been racing for a long time and was pretty good) told me he'd start with 4 gaskets and as the motor wore he'd remove gaskets till it got down to one and at that point the motor was pretty much worn out. Based on what Paul is saying it kinda makes sense.
Personally, i would set the compression based on tach and ability to needle.
Personally, i would set the compression based on tach and ability to needle.
Similar topics
» homemade gaskets
» Pee Wee Head gaskets
» .049 Head Gaskets
» 049 Glow Head Gaskets - 25 Pack @ bargain pricing
» Free Cox merchandise to first 15 people!
» Pee Wee Head gaskets
» .049 Head Gaskets
» 049 Glow Head Gaskets - 25 Pack @ bargain pricing
» Free Cox merchandise to first 15 people!
Page 1 of 1
Permissions in this forum:
You cannot reply to topics in this forum