Priming engine

loka

loka

Active Member
The motor is a new 836, never been fired. I cranked it over for about two minutes with no build in pressure. I have a gauge at the port just above the points cap and an oil light which didn't go out either. I won't fire it until i have pressure.


Just wondering how long it should take to build oil pressure?
What should a good pressure reading for this motor be?

JJ
 
dont know much about the cb750 exactly, but i know hondas suck at keeping oil pressure. i would think that it wouldnt be able to build enough pressure until actually running... if you used assembly lube when you put it all together i dont see anything major going wrong by firing it and letting it run a couple minutes.
 
But if the oil pump is gear driven and the internals are spinning then it should build pressure without firing. I'll check to see if the oil has reached the filter yet, that may tell me more.

And yes, it is a big bore 750, but not as big as i could have gone here or as big as i have gone elsewhere. My Austin Healey Sprite came with a 948cc. The block was lost so i bought a later 1275 and offset bored it 120 thou over to a 1380. Now it's a fun car. Almost tripled the output.

Bigger isn't always better but i'm sure having fun with the results ;)
 
yes, it should build pressure if things are moving, but its like trying to suck water through a 2inch pipe... you simply need to push the pump at a higher rpm to get it to build pressure.

someone please correct me if wrong... im just going based off of what ive seen in life.

big bore shouldnt make a difference in oil pressure either unless if the oil passages were modified.

that makes me think... did you check that all passages are clear? did you use too much assembly gasket maker stuff? any of these things could clog passages no problem.
 
Cranking it over with the plugs out should spin it fast enough to get some oil flow.

Umm....do you have oil in it??... ::)
 
excellent idea hillsy, i will try to spin it over with the plugs out tomorrow on a fresh batt. And yes 3.5litres.

I'm pretty sure the oil galleys are clear and it was just a rebore and reseal, everything else was ok.
 
It probably wont build enough pressure just cranking it. The oil will start moving though, enough to get at least a bit up to the top end... I know my car, also an older honda, will not build enough pressure to trip the switch just cranking over though, and the pressure switch trips at about 5psi... Which is really low.

I would crank it over for about 20 or 30 seconds, and then start it up and let it run for 4 or 5 seconds to see if the pressure light goes off. If its not off within the first few seconds, you have a problem, but probably will not have done any damage to the motor if you put it together using assembly lube as mentioned above.
 
Spin it over without the plugs. You should see the guage beginning to work. Quickly install the plugs. Give the carbs a shot of starting fluid. Hit the starter if you want, but I find a good solid kick on the kick starter works better.The bike should fire immediatly, and build presure.
 
I was planning on firing it tonight but my dog has gone into labour, should be a long night. Will do it tomorrow.

JJ
 
loka said:
I was planning on firing it tonight but my dog has gone into labour, should be a long night. Will do it tomorrow.

JJ
Click to expand...

well... thats something you dont hear everyday! take pics :D
 
Remember doing an oil change on your clunker,,drop, change the filter, add oil. What do you hear for about 4 seconds when you start it up,,,,usually the main bearings pounding,,,and then it goes away, the oil film protects the bearings until pressure is reached. as for your cb 750,,,it uses a remote tank and plumbing,,,if all is well it should produce sufficent oil pressure when fired up..........good luck with your puppys ::)
 
Rocan said:
dont know much about the cb750 exactly, but i know hondas suck at keeping oil pressure. i would think that it wouldnt be able to build enough pressure until actually running... if you used assembly lube when you put it all together i dont see anything major going wrong by firing it and letting it run a couple minutes.
Click to expand...

You know nothing about these, be quiet please.

You probably have feed and return lines swapped over
 
crazypj said:
You know nothing about these, be quiet please.

You probably have feed and return lines swapped over
Click to expand...

haha, never claimed i did... just gave my two cents. and know nothing? Mind you pj... i did a good bit of research on the 750 before i got my 350... it was the bike i originally wanted before i realized its a bit large for me.

but yeah, ill keep quite. ;)
 
Personally, not much of a fan of CB750, its really just a oversize, overweight 500 until you do some serious work (claimed 67 bhp, some were as low as 35~40bhp out of the crate, not much more after service)
836 is a different beasty though (except generator cover still bangs on the floor cornering) ;D
Modified CB500/550 is narrower, lighter and handles better (and not too bad on a 1200+ mile run, been there done that)
 
Rocan said:
well... thats something you dont hear everyday! take pics :D
Click to expand...

IMG_2582.jpg


Not a great pic but they are huddling for warmth as they are only 8 hours old. Had three but there were delivery complications with the first so we have two bouncing boys.

As the bike is being assembled in the house i may have to wait to fire... or roll it outside this weekend, weather dependant. Momma can't get freaked.
 
This is her third and last litter. Normally i sell them as Boston Terriers are very desireable here but i have decided to keep one and give one to my neice/nephew for their b-day.

I'm done breeding Lola, but may look for another girlfriend for Loki.
 
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