Temp of HT's

Discussion in '2-Stroke Engines' started by geebt48cc, Jul 12, 2012.

  1. geebt48cc

    geebt48cc Member

    Been a few guys,

    I 've been wondering what the overall best temp for the littles engines is when running?? I know that depends on alot of things, but wonder what the average temp for best overall live spand would be on 2/stroke HT?


  2. Fabian

    Fabian Well-Known Member

    I would think that the best temperature is the lowest that you could get away with, without loosing significant power.

    My 2-stroke HT engine runs a max of around 280 ºC or 536 ºF (cylinder head temperature) and a max of around 560 ºC or 1040 ºF (exhaust gas temperature), when the engine is on it's knees; working it's guts out (at 5,000 rpm) hauling a heavy load up a steep incline at around 6 mph with the BoB IBEX trailer hanging off the back of the bike for extended periods of time; having little forward airflow over the engine.

    There seems to be a surprisingly stable relationship of 2 x cylinder head temperature to exhaust gas temperature (using the celcius scale) when the air/fuel ratio is correct.
    Last edited by a moderator: Dec 18, 2015
  3. Fabian

    Fabian Well-Known Member

    The thing that (in my case) has the greatest influence with longevity of HT engines is a correct ignition curve.
    The standard CDI has an ignition curve completely unsuited to a 2-stroke engine; useful only for pounding out the connecting rod bearings and shortening the life of the engine.

    Fortunately the Jaguar CDI fixes this problem with an ignition curve correctly suited to 2-stroke operation.
  4. geebt48cc

    geebt48cc Member

    So, Fabian, you do subjest the Jag CDI? I've been thinking about getting from JN? See, I weigh 260, and then 29"bike with side panniers. I'm using 66cc Skyhawk, 600 miles, ave 25mph..............32max. I try to always run in mid 20's with only Castor/Amsoil synthetic 25:1

    Just wonder how much longer it would make engine last? .....................PS-Also, about 300 miles ago on this engine, I milled head down and took head gasket off. I'm also very sure that that makes it run even hotter.

  5. geebt48cc

    geebt48cc Member

    11506.jpg So, Fabian, you do subjest the Jag CDI? I've been thinking about getting from JN? See, I weigh 260, and then 29"bike with side panniers. I'm using 66cc Skyhawk, 600 miles, ave 25mph..............32max. I try to always run in mid 20's with only Castor/Amsoil synthetic 25:1

    Just wonder how much longer it would make engine last? .....................PS-Also, about 300 miles ago on this engine, I milled head down and took head gasket off. I'm also very sure that that makes it run even hotter.

  6. Fabian

    Fabian Well-Known Member

    My experience has been positive with the Jaguar CDI, as previously (with a standard CDI) all my five engines failed within 700 kilometers, of which 3 of them were rebuilt with new crankshafts.
    The current engine i'm running has exceeded 10 times the distance of the other engines and the only difference has been the Jaguar CDI.

    I was somewhat skeptical of the benefits of the Jag CDI, but (in my case) it's proven itself to be quite reliable as well as improving the reliability of the engine.
    Adding higher compression to the engine with the standard CDI is a recipe for detonation and early failure of the big end connecting rod bearing assembly.
    Regardless of the high comp head, you still need a correct 2-stroke ignition curve, which the standard CDI is not.
    Last edited: Jul 12, 2012
  7. geebt48cc

    geebt48cc Member

    Fabian, I'm going to order the Jag CDI. I really hope that it isn't to late considering I'm right at 600 miles now. So, everything still seams to be ok with the connecting rod bearing assembly, but knowing my luck, it's just getting ready to fail??????????? I'm going to order, but wonder if it's just a matter of time in breaking, despite putting new Jag CDI on? Guess what I'm asking is, could that rod bearing already be damaged, or wonder if it would just break all at once?...........Uno, giving me time to replace it with the better Jag CDI????
  8. Fabian

    Fabian Well-Known Member

    Oh goodness - 600 miles on an engine with a standard CDI is pushing your luck with longevity of the connecting rod big end bearing, especially if it's had a good dose of high rpm - you might have a little more insurance if the big end bearing is of the crowded roller type, but detonation is still detonation, regardless if the engine is fitted with a crowded needle roller bearing setup.

    The rod bearing from my experience doesn't just instantly fail and lock up the engine, though it's happened to some.
    Typically what happens is that the engine starts to rattle and the rattle becomes louder and louder to the point where you think it's going to totally fail - generally you'll replace the crankshaft and rod before it completely locks up as the rattles become unbearably loud.
  9. Fabian

    Fabian Well-Known Member

    This is my post from a few years ago pictorially describing the effect of excessive ignition advance, but most importantly detonation on the big end connecting rod bearing from the standard CDI.

    At the time i did not know that the standard CDI had a 4-stroke ignition curve and was pounding the heck out of the big end, of which i compensated for the overly advanced timing curve with a large jet size.

    This is what detonation looks like - bear in mind that this engine was never revved over 4,000 rpm in it's relatively short 700 kilometer life; with all subsequent engines failing at virtually the same distance from exactly the same failure.

    Photo tutorial:

  10. geebt48cc

    geebt48cc Member


    I also wanted to ask you if you can really see alot of difference in your bikes performance with your new CDI?


  11. Fabian

    Fabian Well-Known Member

    There was virtually no (peak power) performance gain with the Jaguar CDI, though there's been a significant increase in big end connecting road bearing life with the Jaguar CDI, which is what you would expect a proper 2-stroke ignition curve to achieve.

    Firstly, i want a reliable engine,
    Secondly, i want a reliable engine,
    Thirdly, i want a reliable engine,

    With the Jaguar CDI, i have a mechanically reliable engine.

    If you want quick and easy way of gaining more "usable" performance, get a Rock Solid Engines, Reed Valve Intake.
    It (in my experience) won't give you more peak power but it will noticeably improve bottom and mid range torque, allowing you to go the same speed, using less revs and generally have a more muscular power delivery, not to mention a great reduction in noise coming from the air filter.

    Ultimately, if wanting "more power" the only real (and reliable) option is a "Morini Engine" - you're just wasting time and money on a Chinese engine, trying to significantly improve it's power output.

    Morini Engine: http://www.morinifrancousa.com/engines.htm
  12. geebt48cc

    geebt48cc Member

    No, I believe everything you are saying. Fabian, the"Morini" is something else. RELIABLE is just what I'm after. True, we are still talking china stuff here, but time will tell. Just was wondering if you noticed anymore torque or heat relief?

  13. Fabian

    Fabian Well-Known Member

    With or without the Jag CDI, the Exhaust Temperature Gauge showed no noticeable difference in temperature.
    I also didn't notice any meaningful increase in torque with the Jaguar CDI compared to a standard CDI - all the extra low and midrange torque came from the Rock Solid Engines Reed valve Intake.

    Another trick to improve the power curve of the HT engine is piston ramps. I'll send you a PM on how it's done and why it works.
  14. geebt48cc

    geebt48cc Member

    Wow, I've not seen the piston itself ramped, just some work on the jug itself. Well, I'm playing the waiting game for my new Jag CDI. No, Fabian, I know that these little engines are only able to put out so much power. I just hope that ordering the Jag CDI for $88 dollars will be worth it on a $160.00 Skyhawk 66cc kit? I really don't push the engine over mid twenties, but will run on flat 30+. Considering I'm a big guy at 6' 6", 260, everything we've talked about helps. Living in SW Va. with a fair share of hills, general power does help. I know that we are talking about small cc's here on just bicycles, but I just want it to run the best it can. (lol, even though it's made in china)

    Anyway, it's synthetic/castor at 25:1 with 600 miles sense new. Hope that this new CDI will at least give it another 600 miles of service. Fabian, when it had right at 300 miles, I milled head, and just removed head gasket. That really helped overall with also extending the intake on carb 7". Torque really jumped up. This new Jag CDI should not only help wrist pin bearing to live, but also smoother, and easier starts.

    Fabian, what was the main thing that you noticed that the Jag CDI did to your bike?

    Appreciate you sending the link.

  15. Fabian

    Fabian Well-Known Member

    After an initial test run, i decided to increase the ignition curve to the maximum by removing "all" jumpers. It must be noted that my engine doesn't require any of the lower advance curves because it's using the standard, low compression cylinder head - the performance seemed to increase (on my engine) using the maximum setting over the factory installed setting.
    Having said that, you may need a different setting if running a high compression cylinder head without a head gasket or other performance modifications.

    My first trip with the Jaguar CDI fitted gave me the impression of a more gentle level of vibration - the engine almost felt like it had less power but the speedo showed no loss of speed travelling over identical routes and inclines. The actual performance remained the same - in my case there was no discernible power gain or power loss but it was a more enjoyable riding experience with reduced vibration coming from the engine.

    I'm positive that your engine will have good reliability and reasonable life if it's fitted with a crowded needle roller big end, as well as the Jaguar CDI and 25:1 oil/fuel ratio.
    Installing a Rock Solid Reed Valve Intake will also help as there is much less need to excessively rev the engine to make usable power.
    With the reed valve intake and the Jaguar CDI, little is gained by going over 5,000 rpm, which contributes to engine life and reliability.

    This combination (and piston ramps) gives the engine enough torque that excessive revs are not needed.
    Last edited: Jul 19, 2012
  16. Waxxumus

    Waxxumus Member

    Mine has been running 1400 km on stock cdi.
    What about your engines makes them keep dieing?
    Do you run WOT the whole time?
  17. Waxxumus

    Waxxumus Member

    25:1 what?!?!
  18. crassius

    crassius Well-Known Member

    2012 thread
  19. butre

    butre Well-Known Member

    he runs up hills overloaded and kills bottom end bearings. the rest of us are breaking the cages on the top end. it's why I use a bronze bushing in the top, so when I inevitably destroy it I don't ruin my expensive CNC machined head and jug that I put a ton of hours into
  20. jaguar

    jaguar Well-Known Member