Argess
Posts: 2323
Score: 151
Joined: 1/12/2006
Last Login: 5/23/2013
From: Pleasantville,
NS, CANADA
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You probably won’t want to hear this, but the Force 26 was the worst engine I ever owned.. I always found it very touchy engine to tune without it getting way too hot. And by that I mean well over 300degF for decent performance, but detonation starts about 325degF with the Force 26. You can hear at idle after it comes in after a few WOT runs. Idle is higher than normal, and it makes sort of a sizzling sound. To be fair, I do a lot of WOT runs, and over grass, which contributes to making an engine run hot.
So I experimented.
First thing was the fuel. Dropping to 12% oil made a significant difference in ease of tuning, engine performance and reduction in head temperature. I didn’t go lower as this was the best I could do with what my LHS had available. Just the brand can make a difference too. For example, I find Blue Thunder runs cooler than Morgan’s Sidewinder. Whatever you do, don’t use Backyard Basher. Way too much oil (16%), and causes all kinds of problems.
I also have a Force 28 which has always run great. Completely different than the Force 26. The Force 26 heatsink has always appeared to me to be insufficient for it's task.
I did a comparison of the Force 26 with the Force 28. Rough approximations, but close enough to get the picture:
1/ Force 28 has 7.7% larger displacement than the Force 26
2/ Force 28 has 12.5% more power than the Force 26
3/ The Force 28 head has "approximately" 32.3% more surface area than the Force 26.
4/ I have had no troubles with overheating from the Force 28.
More research revealed the OFNA head was cast which dissipates heat more poorly than a machined billet head. Regardless, a larger aftermarket head solved my troubles with this engine, but not my curiosity. Basically, I wanted to reduce the heat at it’s source, not band-aid things up by merely dissipating all this extra heat by using a larger cooling head.
After a little more experimenting, I found an additional improvement in running cooler by using an OS A5 plug. This is a short plug and helps reduce the compression ratio a bit. Similar idea as adding a head shim.
So eventually I tried adding an extra head shim to mine and the temp drop was incredible, plus the engine ran great! Unfortunately I didn't allow for a bit more break-in at the new cooler temp and kept pushing the engine to get more heat. The crank pin finally broke. Mind you, the engine had many, many gallons on it, plus I experimented a lot with this engine, so it was sort of “abused”.
I'd like to say add another head shim, plus go back to a MC8 plug is the answer for the Force 26, but as mine did self-destruct when I did it, I'd be careful doing that.
I remember having a tough time breaking the Force 26 in as well. I got a lot of blisters from mine for quite a while. I eventually converted to Roto-Start, which worked great.
During Break-In, I also had a lot of fuel dripping out the pipe. Can’t remember for sure why that was, but one thing I have found for Break-In is to do a rough adjustment on the LSN for best idle. Just tune it so the engine will idle for at least 15 seconds or more. Just listen to it. If it slowly speeds up, then you need to richen the LSN a bit. If it slowly bogs down, then lean the LSN a little bit. This isn’t necessarily the best tune for performance in the vehicle, but it helps keep the Break-In going smoothly. Nothing more frustrating during Break-In than an engine that always stalls.
In contrast, don’t forget to keep the HSN rich for Break-In, leaning it little by little as you go through tanks of fuel. But too rich isn’t good either as the engine can bog to the point it stalls causing more frustration. I find the HSN has to be set a little bit leaner than the Factory recommended settings for Break-In.
However, back to the Roto-Start thing. I sort of did it all backwards. Should have installed Roto-Start for Break-In, and then went back to Pull-Start after that. I like Roto-Start, but it’s a big heavy thing to stick in your pocket when you have to go make a re-start “some-where-out-there”..
So....go with the OS A5 plugs, convert to Roto-start if you can, break them in individually for the first 2 to 3 tanks and keep them rich enough they don't exceed 300degF.
The OFNA buggy guys told me the Force 26 runs much cooler with 30% nitro and this makes tuning easier. I’m not sure if this correlates with me adding a head shim because I use 20% or not. Anyway, I havn't tried it, but you might want to consider it.
In a nutshell, here’s things that can help with your Force 26:
1/ Use fuel with a lower oil content. I’m happy with 12%, but no doubt you can go lower.
2/ Use an OS A5 plug (I think the part number has been changed to OS #10)
http://www.osengines.com/accys/glowplugs.html
3/ The, the Force 26 should start with the LSN "flush" and the HSN about 1.5 to 2 turns in from flush. The LSN is probably never adjusted more than 1 turn in from flush, and the HSN can be almost anywhere, but typically 2.5 turns in from flush once broken in. The LSN is often about 1/2 turn in from flush once tuned, and I think is safe for Break-In.
4/ Once Break-In is over, and you start tuning for performance, a common mistake is thinking the engine is tuned well, but it seems way too hot after doing some WOT runs. Typically this is due to the HSN being too lean and the LSN too rich. As the engine revs up, it seems OK, but actually runs lean once the excess fuel from the rich LSN burns off. Tune your LSN to avoid this.
5/ You can try 30% fuel and see how you like it. No doubt you will have to re-tune things a bit.
6/ Install a Roto-Start. You can go back to a Pull-Start after Break-In if you like.
7/ I wouldn’t recommend trying an extra head shim (plus offsetting that type of serious change a bit by going back to a long plug, like the MC8) just yet. It’s a new engine, and since that type of experimenting can go terribly wrong, it would be a shame to see it self-destruct.
Ps: My Force 26 was purchased new back around 2006 or so. It’s possible yours is different, so some things I mentioned may not apply, such as “turns in”, etc
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All Forums >> RC Cars, Buggies, Trucks, Tanks and more >> RC Car Engines >> Car Nitro & Gas Engines >> what mixture of fuel do you guys use? 
what mixture of fuel do you guys use? - 
, no, it won't harm the engine at all. Regardless of temperature, the piston rides on a film of oil which is what keeps it seperated from the liner. So long as that oil film is continuous there's no contact so no wear and it's the oil film that holds the seal against compression, not the "pinch". 