D
Deleted member 12676
Guest
of course you can't put your hand on a 400 degree metal surface.
Cylinder head/Fred head
- Thread starter barnett256
- Start date
My head whent really well feels better all the way from bottom to top.5 to 10 kmh better but at 60 65kmh it starts to play up i got a 20inc whith 36 t and maybe iam ringing it out my plug gap is huge but new cdi is priced to hi in Australia what if it doesn't go better with a hi performance one I can get a new kit for $130 after posting the cdi is the same price??? What to do
D
Deleted member 12676
Guest
you might be losing spark at high rpm due to excessive plug gap
But it goes better with bigger gap. I heard one man say he uses a 8 spark plug and I got a 5 6 and 7 all go good to start you hit 40kmh open them and then 50 open more and 60 some kids I build bikes for have new kits I think like a stock plug open it and thay don't start close it right down and off like a rocket. If I put my 28 t on it needs a pedel to start but then it pulls up to 60 /65 and is not reving hard but just won't get over a flat spot and rev out. Getting new plug today if I can I will make videos of it going so you can see or hear it
Or maybe I make the speed carby change needle on the go I am one off the bottom but it makes a wet plug when at bottom so when at hi speed it might work and what do you think of the stock muffler empty with a coin at the end or disk that can close or open at will I have one it can go as quiet as stalling on idel or like a Lamborghini when open mine is a steel pipe not the stock one 1inc longer works on a gear changer cable and spring you see cops and turn it down I love it
sbest
Active Member
Jaguar and Butre and a couple others, you are worth reading. Thanks for being there...
I did a lot of work on cylinder head chamber shapes and volumes, and rebuilding and modifying 2 stokes on snowmobiles, bikes and most recently Blaster quads, since the 1970s. I've stuffed, timed, cut, filed, ported and swapped. My experience is with 125-250cc engines. Jaguar, I really respect your website and CDI box. Excellent work. I only have limited experience with my pre-used HT motor. I checked and set the squish while getting it reliable with an overall bolt check, but I feel I have to wade in on the head issue.
First of all, chamber shape is most critical to combustion characteristics, comparatively more than compression ratio. A wide squish band and tight flat pocket combustion chamber support low rpm torque better. The best shape for broad torque is a torroidal chamber that will support a donut shaped tornado of twirling combustion. The squish has to be set (on a 125 anyway) to 0.5 to 1mm max to get this effect. The present HT head supports high rpm power and the squish was off on mine at 1.5mm.
Jaguar is right about cranking pressure, but head volume, compression ratio and port timing all go hand in hand. Set the port timing highter and you can raise the CR without putting the cranking pressure too high. One balances the other. Compression ratio mainly affects the low rpm and tends to drive heat into the head and piston if too high. Jaguar is right about needing more timing retard at higher rpm. critical. In fact, the more power you make, the better the combustion shape, the less timing advance a 2-stroke needs.
About plugs, READ THEM. The condition of the the deposits on the insulator near the electrode tip tells you about the plug heat range. First however, you have to have the carb mixture right. That is read on a new plug insulator down next to the shell after a long full throttle run. We sometimes even cut the threads off the plug to see this area to read it. Just looking for a brown soot ring at the base of the insulator.
Even before that, check for vacuum leaks. 2 strokes are very vulnerable to vacuum leaks. Plug the intake and exhaust and pump up the cylinder and crankcase to 5-7psi with a handpump and see how long it holds it. 3-5 minutes would be a minimum. This is an important test for seals and gaskets.
Butre, I am interested in this bronze rod bearing idea. We used to use them in our universal joints when drag racing for the same reason. Many old outboard engines used them too, but used lots of oil and low rpm. Modern roller bearings have proven able to stand up, so what is the failure mode? I am guessing a bronze bushing would only be needed to overcome:
1) poor rod bearing surface hardening
2) poor pin hardening
3) poor roller quality
4) detonation problems
Thoughts?
Steve
I did a lot of work on cylinder head chamber shapes and volumes, and rebuilding and modifying 2 stokes on snowmobiles, bikes and most recently Blaster quads, since the 1970s. I've stuffed, timed, cut, filed, ported and swapped. My experience is with 125-250cc engines. Jaguar, I really respect your website and CDI box. Excellent work. I only have limited experience with my pre-used HT motor. I checked and set the squish while getting it reliable with an overall bolt check, but I feel I have to wade in on the head issue.
First of all, chamber shape is most critical to combustion characteristics, comparatively more than compression ratio. A wide squish band and tight flat pocket combustion chamber support low rpm torque better. The best shape for broad torque is a torroidal chamber that will support a donut shaped tornado of twirling combustion. The squish has to be set (on a 125 anyway) to 0.5 to 1mm max to get this effect. The present HT head supports high rpm power and the squish was off on mine at 1.5mm.
Jaguar is right about cranking pressure, but head volume, compression ratio and port timing all go hand in hand. Set the port timing highter and you can raise the CR without putting the cranking pressure too high. One balances the other. Compression ratio mainly affects the low rpm and tends to drive heat into the head and piston if too high. Jaguar is right about needing more timing retard at higher rpm. critical. In fact, the more power you make, the better the combustion shape, the less timing advance a 2-stroke needs.
About plugs, READ THEM. The condition of the the deposits on the insulator near the electrode tip tells you about the plug heat range. First however, you have to have the carb mixture right. That is read on a new plug insulator down next to the shell after a long full throttle run. We sometimes even cut the threads off the plug to see this area to read it. Just looking for a brown soot ring at the base of the insulator.
Even before that, check for vacuum leaks. 2 strokes are very vulnerable to vacuum leaks. Plug the intake and exhaust and pump up the cylinder and crankcase to 5-7psi with a handpump and see how long it holds it. 3-5 minutes would be a minimum. This is an important test for seals and gaskets.
Butre, I am interested in this bronze rod bearing idea. We used to use them in our universal joints when drag racing for the same reason. Many old outboard engines used them too, but used lots of oil and low rpm. Modern roller bearings have proven able to stand up, so what is the failure mode? I am guessing a bronze bushing would only be needed to overcome:
1) poor rod bearing surface hardening
2) poor pin hardening
3) poor roller quality
4) detonation problems
Thoughts?
Steve
Last edited:
butre
Well-Known Member
the typical failure mode is the cage breaking and the rollers falling all over the place. a better bearing can prevent that, but bearing failure is still catastrophic while bushing failure is gradual and doesn't leave a bunch of hardened steel pins floating around in your engine.
as for the oiling issue, I get around that by simply drilling a hole in the bushing to match the hole already in the connecting rod.
I've considered rifle drilling the connecting rods as well, but I don't have any bits that long under a quarter inch so I haven't tried it
as for the oiling issue, I get around that by simply drilling a hole in the bushing to match the hole already in the connecting rod.
I've considered rifle drilling the connecting rods as well, but I don't have any bits that long under a quarter inch so I haven't tried it
Sorry this phone is ****ing me i think more petrol wood get more out of it but it's been off for 30 Mins and still hot as all he'll but that 1mm off the head is grate may be some fins bolted on to help with the heat and iam done lol for now
