- Thread starter Laspaz
- Start date
I am trying to calculate the CFM to see if this trailer compressor trumps my existing one:
Now that the trailer compressor runs, I was able to run some basic online calculations to give me an idea of the CFM. It took 3 mins to pump up to 100psi, with the 100l tank. Apparently that is in the ball park of 7.6 - 7.9 CFM. Also this thread: http://www.mig-welding.co.uk/forum/threads/new-project-compressor.50470/
that is the same pump says the bore is 2 5/8" and stroke 2" with a normal RPM of 950. This volume (x2 for both cylinders) works out to 13.7 CFM.
That makes the air I am getting a little low right? I'm not sure what RPM I am spinning, but the engine has a governor to run at a set RPM, so it should be right?
Any thoughts? Cheers.
Now that the trailer compressor runs, I was able to run some basic online calculations to give me an idea of the CFM. It took 3 mins to pump up to 100psi, with the 100l tank. Apparently that is in the ball park of 7.6 - 7.9 CFM. Also this thread: http://www.mig-welding.co.uk/forum/threads/new-project-compressor.50470/
that is the same pump says the bore is 2 5/8" and stroke 2" with a normal RPM of 950. This volume (x2 for both cylinders) works out to 13.7 CFM.
That makes the air I am getting a little low right? I'm not sure what RPM I am spinning, but the engine has a governor to run at a set RPM, so it should be right?
Any thoughts? Cheers.
normspanners
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that seems a little low???
mine with a similar pump and using a little honda 7 hp even at idle pumps to 150! with no problem.
Are you sure the governor is working? it is probably seized I,m pretty sure they work off the fan on those old engines ie they keep the same airflow over avane that open the throttle and increases the throttle opening but not increasing engine speed, abit like having to open up you car throttle on a hill because of the extra load of the hill but not wanting to increasing actual speed.
Gareth J
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Once your new one is operating as good as you think it will, compare the two by either fitting the same 1/4" bore fitting to both comps and see which one can maintain the highest pressure. Or, even better, put a valve on the output and see which comp let's you open the valve farthest while maintaining your normal working pressure (~90psi?)
Bill Edwards
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If you could get hold of a tacho then measure the rpm, it's impossible to decide if it's outputting less than it should be without knowing if the speed is correct.
It doesn't sound right to me for the engine to stall at 125 psi, I suspect something isn't right.
It doesn't sound right to me for the engine to stall at 125 psi, I suspect something isn't right.
I can't see a check valve anywhere on the compressor. Would this cause the air pressure to feed back to the head and make it struggle at higher RMP?
Otherwise I can pull the head off the pump and check everything out. Does anyone know what the bolts should be torqued to when I put it back on?
Otherwise I can pull the head off the pump and check everything out. Does anyone know what the bolts should be torqued to when I put it back on?
the engine isn't particualy powerfull 2.5 bhp @ 2500 rpm , 2.7 @ 3000 probaly find its running out of torque at the higher rpms. these old enignes can greatly benifit from an exhaust silencer that isa littel more sympathetic to flow and is less cork like as far as the engine is concirned ( probaly become quiter as well. same gose for the intake. points gap has a hell of effect on there output as well.
normspanners
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Yes also;
With a tacho if the engine speed drops off slowly, as the pressure builds it is quite obvious the governor is seized, and not opening the throttle.
I have ordered a RPM meter, so shall see what's going on there in a day or two.
The governor does move freely, and I set it at max travel with some vice grips in case the spring was worn out, and it made no difference.
The whole unit does have a slow cyclical hum/vibration, but the engine seems to run great until it hits about 115 psi, then slows progressively till it stalls within the next 5-10 psi.
The governor does move freely, and I set it at max travel with some vice grips in case the spring was worn out, and it made no difference.
The whole unit does have a slow cyclical hum/vibration, but the engine seems to run great until it hits about 115 psi, then slows progressively till it stalls within the next 5-10 psi.
Meter has arrived, and the results are in.
With vice grips setting the governor to maximum, 2100 rpm for the engine, and 550 rpm for the pump. The pump is supposed to run at 950 rpm. So my pump pulley is 11" and my engine pulley is 3". To get around 950 rpm at the pump, I need around 3500rpm from the engine.
A newer Honda 6.5hp is claimed to run at 3600 rpm, but would it be made to run constantly at this speed while I used the compressor? Kinda loses the vintage look too. But I guess function>form.
Also noticing some smoke coming out of the engine case through this (pictured below) breather? Is that a concern? And then some photos now it's cleaned up a bit.
With vice grips setting the governor to maximum, 2100 rpm for the engine, and 550 rpm for the pump. The pump is supposed to run at 950 rpm. So my pump pulley is 11" and my engine pulley is 3". To get around 950 rpm at the pump, I need around 3500rpm from the engine.
A newer Honda 6.5hp is claimed to run at 3600 rpm, but would it be made to run constantly at this speed while I used the compressor? Kinda loses the vintage look too. But I guess function>form.
Also noticing some smoke coming out of the engine case through this (pictured below) breather? Is that a concern? And then some photos now it's cleaned up a bit.
normspanners
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It can run at a lower speed that is just the recommended max. the pump geared slower is better for the engine.
BTW is the governor rod adjustable ? when on max with the engine not running take off the air filter and look at the butterfly in the carb it should be wide open if not the goveror is not set correctly.
If it is try taking the exhaust off the head and run it as said earlier the silencer could be gummed up might need burning out with oxy.
normspanners
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piston rings could be worn, is it starting ok ?
Yep, it's starting well, usually first pull. Will try your suggestions in #31 and report back.
Would like to run the pump closer to 950 rpm, because at it's current speed (550rpm) it's not producing enough CFM.
The carb does not have a butterfly visible from the air cleaner, as it's higher up. It's certainly moving freely and has full range from the lever connect to it. The exhaust is also flowing freely.
Here are some photos showing the set up. I use the vice grips to make up for the slack in the worn spring. It pulls the governor to it's maximum position and boosts the engine RPM by about 200.
Here are some photos showing the set up. I use the vice grips to make up for the slack in the worn spring. It pulls the governor to it's maximum position and boosts the engine RPM by about 200.
octo0072000
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ignore the governor when it's running at max revs try opening the butterfly the bit with the idle screw in it that looks to need to be opened more than it is see if it revs up when you do that
I unscrewed the screw and now it's spinning at 1800 rpm with the pump at 480 rpm. If I push the butterfly in, the engine slows. If I pull it out, the engine hunts slightly.
Also noticed a few bubbles coming out where you see the oil in the photos below. Might be loose, but didn't want to try and tighten it with the engine warm.
normspanners
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That screw is the idle screw unscrewing the screw will slow it, the governor should try and fight the spring ie move the butterfly away from the spring most engines will easily stand 2500-3000 rpm and blips to 4000 -5000 with no worries. the compressor should not be taken much above it max of 1000 btw
the oil looks like crankcase compression, there might be a blocked breather, if it is starting ok I would think the rings are doing the job and not worn excessively or the piston oil rings might be gummed up, another cause can be the glazed bore , also maybe years of running with the engine running too slowly, ? if glazed bore that can right itself by you, making the engine work harder, BUT dont use modern thin synthetic oil it is too good at lubrication for keeping bores toned.
As the engine runs at the moment it might be worth stripping it now before any lasting damage is done, the old girl looks worth the effort.
did you check the engine speed from empty that will tell you if the governor is working the speed will gradually drop off.
PS dont see how the grips effect the speed where they are at mo moving the butterfly away from the springs revs it more.
AHAH I see NOW if that spring has slack and putting the grips under the washer lifts it and makes the governor job a little harder that spring needs to be WAY stronger than it is, it is vastly stretched it is the springs job to pull the throttle open--- against the governor.
if the engine then hunts the carb needs stripping and cleaning as the engine is not getting enough fuel
the oil looks like crankcase compression, there might be a blocked breather, if it is starting ok I would think the rings are doing the job and not worn excessively or the piston oil rings might be gummed up, another cause can be the glazed bore , also maybe years of running with the engine running too slowly, ? if glazed bore that can right itself by you, making the engine work harder, BUT dont use modern thin synthetic oil it is too good at lubrication for keeping bores toned.
As the engine runs at the moment it might be worth stripping it now before any lasting damage is done, the old girl looks worth the effort.
did you check the engine speed from empty that will tell you if the governor is working the speed will gradually drop off.
PS dont see how the grips effect the speed where they are at mo moving the butterfly away from the springs revs it more.
AHAH I see NOW if that spring has slack and putting the grips under the washer lifts it and makes the governor job a little harder that spring needs to be WAY stronger than it is, it is vastly stretched it is the springs job to pull the throttle open--- against the governor.
if the engine then hunts the carb needs stripping and cleaning as the engine is not getting enough fuel
Yep the vice grips pull on the spring holding it in the maximum position. The rod can not open any further.
I will play a bit more today and see if I can get some higher RPM from the engine. I certainly don't want to take the compressor pump above 1000. If I can get the engine to run faster, then I am happy to rebuild it. If I can't get it going faster, then it needs to be replaced.
The RPM of the engine does slow over time as the tank fills. It lost around 100 RPM at the pump from start to finish (115psi).
I have stripped and cleaned the carb, but the hunting seems to be part of the basic carbs nature, as the manual talks about a special damping spring that can be tightened once it starts hunting.
I will play a bit more today and see if I can get some higher RPM from the engine. I certainly don't want to take the compressor pump above 1000. If I can get the engine to run faster, then I am happy to rebuild it. If I can't get it going faster, then it needs to be replaced.
The RPM of the engine does slow over time as the tank fills. It lost around 100 RPM at the pump from start to finish (115psi).
I have stripped and cleaned the carb, but the hunting seems to be part of the basic carbs nature, as the manual talks about a special damping spring that can be tightened once it starts hunting.
Gareth J
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If you're considering going to go to the hassle of rebuilding, if this is a working (as opposed to ornamental) compressor, I'd just stick a used Honda on it and be done. They're a bit more refined. If you can get that one running well though, that should be the easiest solution, there's not a lot to go wrong.
What would concern me more at the moment is that it looks like someone has welded mudguard brackets directly to the side of the tank. Prime for fatiguing as the guards wobble over bumpy roads. Maybe I'm seeing it wrong but that's what it looks like.
What would concern me more at the moment is that it looks like someone has welded mudguard brackets directly to the side of the tank. Prime for fatiguing as the guards wobble over bumpy roads. Maybe I'm seeing it wrong but that's what it looks like.
I have ordered a new engine. Hopefully the 6.5hp will be sufficient.
The mud guards do concern me a bit, but I don't intend to be towing it around very much. I will look carefully around the welds when stripping it back.
Thought I better paint it, so started stripping it down:
The mud guards do concern me a bit, but I don't intend to be towing it around very much. I will look carefully around the welds when stripping it back.
Thought I better paint it, so started stripping it down:
