Topic: Low oil pressure and leak (CB750 F2 engine)

[mazingerzeca]

Hello all.
I have a CB750 K7 with an F2 engine on it. I rebuilt it recently, and since the rebuilt, it is difficult to maintain oil pressure. The red light turns on and an oil gauge that I attached to the engine shows pressure dropping to 10 psi at the same time. If I refill the tank a little, the problem gets solved, but it developes a leak around the cylinder head. I mean that the leak doesn't seem to be on the gasket itself, but somewhere on the head. I even borrowed the oil pump from my other bike just to discard that the problem was there.
My suspicion is that the oil finds it difficult to find the path from the head to the bottom of the engine, which creates a high pressure on the head and so the leak somewhere on the head. If so, which would be the culprit? I installed high torque APE studs, which maybe leave less space on the holes for the oil to pass through. I'm using Actevo 20W-50, maybe too thick? Or maybe I'm wrong and it has nothing to do with any of this. Any ideas?
Thank you.

[PeWe]

I saw sudden oil warning when idling on sidestand direct after start. I opened oil tank cap and saw not much oil.
This on both my bikes CB750 K2 and K6. After that no idling on sidestand without a 2" plank under the sidestand.

I guess the pump got no oil in that angle from oil pan via strainer.
No problem when bike is standing upwards.

[scottly]

Pull a tappet cover off and see if the top of the head is full of oil. If so, you have a drainage problem, most likely from the thicker heavy-duty studs, or possibly a head gasket issue? Also, are the oil restriction jets in place?

[mazingerzeca]

I will check that. Yes, the oil restriction jets are installed. I thought about leaving them off when reasembling the engine, because they seemed to restrict too much, but I left them. Would it be a problem if I leave them off.
As for the head gasket, I don't know. It was a genuine Honda gasket and I didn't use any sealer on it.

[Jerry Rxman Griffin aka MuthaF'er]

How many of the small o-rings that fit around the oil jets did you use? 2 or 4?

[mazingerzeca]

I'm not really sure, but I think that there are two holes with oil jets, and four o-rings. The other two o-rings go inserted on a recess on the head, a blind hole

[bryanj]

If you leave the jets out the crank suffers

[PeWe]

This thread gave me an idea to test the idle on sidestand and oil reaching too low in tank.
Then check inside valve cover at cyl 1 tappet plug if oil level is  high there, oil not return as needed.
The angle of bike can affect this part too. If OK, pump does not suck oil enough from pan.

Both my bikes have the thicker studs and restored pumps.

[Terry in Australia]

We have/had a member here called TwoTired, who'd answer your questions with lots more questions, but he was trying to diagnose the issue. In his absence, I'll ask a  couple. You say you've just "rebuilt" your engine, so what work did you do? Top end rebuild? Split the cases? Overhauled the oil pump? Replaced the main bearings? Big end bearings? Rebore? New pistons and rings? etc etc etc. Tell us what you did mate, and that'll help.

A common oil leaking area on any CB750 is from under the 6 rubber "Pucks" located under the cam towers. If you didn't replace them with new OEM ones, with a smidgeon (and I mean a tiny amount) of sealant around their circumference, you risk having oil leak out of the cylinder head area, running off your fins and dribbling on the ground.

If you installed an F2 head on a non-F2 cylinder block, it will leak under the head, as the oilways are a different shape. If your main bearings are worn out, you will have very low oil pressure, as you also will if the rubber O rings on your oil pump mounts are either worn out, undersize (aftermarket crap) or missing entirely. Of course, if you didn't torque your head down in the correct sequence and in small increments, it'll leak. If you're running APE studs, that in itself won't cause any oil leaks, I've used them for years without issue, but if you only torqued them to 15-16 foot pounds, the head gasket can leak, crank those b1tches down to at least 20 foot pounds. If your head is warped, or the gasket mating surfaces weren't meticulously clean, it can leak.

Did you remember to replace the four 6mm screws with the phillips slots in their hex heads heads under the rubber pucks? I use "allen bolts" (internal hex head bolts)so I can use a 5mm allen fitting on my torque wrench and torque them down, along with the external 6mm screws on the head. I'm drinking heavily, so have probably forgotten something, but let us know what you "rebuilt" to give us a bit of a clue as to what might be the problem.

The F2 engine was the most powerful, but also the most fragile. There are more dead F2 engines than live ones (I own several) and the "Good running F2 club" has a very small, exclusive membership..........    

[mazingerzeca]

Thanks for the replies.
I made a complete rebuilt of the engine. I opened it due to the infamous valve guide wear on F2 engines, and once the engine was out of the frame I made what follows:
- New oil seals and Honda gaskets, o-rings and pucks under the cam towers.
- Flattened head surface.
- New valves and APE bronze valve guides
- Replaced main bearings and big end bearings
- Pistons rebored and new rings
- Overhauled the oil pump.
- APE studs
Yes, I installed the bolts under the cam pucks, although they don't have philips slots on the F2 model.
I made the test you suggested on my bike. I took off the valve tappet cover and there was no oil there, so it seems that it drains well to the oil sump.
The oil light was turning to on from time to time, if I used the throtle, It went off. Checked the oil level and it was low. Refilled it and the oil leak appeared. As the engine was pretty clean, I could see that the oil came from the head gasket, so the problem must be there. The leak doesn't appear running low on oil, but onde the required amount of oil is on the engine, the gasket can't cope with the right amount of oil pressure. Am I right?
As Terry suggested, the problem can be that I didn't torque the HD APE studs enough, I gave them the standard torque.

[PeWe]

"The oil light was turning to on from time to time, if I used the throtle, It went off. Checked the oil level and it was low."

Exactly as my bike when idle on sidestand.
I do not see any problem, just not let it idle leaning to the left too much too long.

Fill more oil here can be emergency for engine.
Oil level  will then  be higher after a 30 min ride?
I had to suck oil out of the tank  since I did not want any oil spray on wheel and bike in general.
(K2 with vent to air)

- Was your bike standing up or leaning on sidestand?

[Terry in Australia]

"The oil light was turning to on from time to time, if I used the throtle, It went off. Checked the oil level and it was low."

Exactly as my bike when idle on sidestand.
I do not see any problem, just not let it idle leaning to the left too much too long.

Fill more oil here can be emergency for engine.
Oil level  will then  be higher after a 30 min ride?
I had to suck oil out of the tank  since I did not want any oil spray on wheel and bike in general.
(K2 with vent to air)

- Was your bike standing up or leaning on sidestand?

How did you suck the oil out Per........?

[mazingerzeca]

I'm afraid I didn't understand quite well, PeWe. Yoiu mean that I shouldn't have filled with oil. I filled the oil to the middle of the reading stick. I assume that the level should be there. If I leave the engine with less oil, it doesn't leak, but the read light wents on and the gauge reads low psi, so the engine is at risk.
Once refilled, the gauge reads 10-20 psi and 60-70 at full throttle, but for sure, If I go for a short ride, it will start leaking all around the head, but leaving the oil under the correct level can't be the solution.

[PeWe]

I used a big syringe with a hose.

- Oil went low when bike was parked, idling before a ride, right?

If bike was parked on sidestand, the angle of the bike caused lack of oil in my bike's tank.
Pump did not fill oil in time due to the bike angle.
Oil pump has 2 pumps, to and from oil tank via the 2 thick oil lines.

[mazingerzeca]

In my case, oil light went on on riding and at idle on sidestand. The oil level was low, for sure.

[newday777]

In my case, oil light went on on riding and at idle on sidestand. The oil level was low, for sure.

Are you checking the oil level on the sidestand or on the centerstand?

[mazingerzeca]

On the centerstand, rode the bike for a while, checked, the level was low. Waited for a minute, low. Waited for some minutes, still low.

[newday777]

Thanks for the replies.
I made a complete rebuilt of the engine. I opened it due to the infamous valve guide wear on F2 engines, and once the engine was out of the frame I made what follows:
- New oil seals and Honda gaskets, o-rings and pucks under the cam towers.
- Flattened head surface.
- New valves and APE bronze valve guides
- Replaced main bearings and big end bearings
- Pistons rebored and new rings
- Overhauled the oil pump.
- APE studs
Yes, I installed the bolts under the cam pucks, although they don't have philips slots on the K7 model.
I made the test you suggested on my bike. I took off the valve tappet cover and there was no oil there, so it seems that it drains well to the oil sump.
The oil light was turning to on from time to time, if I used the throtle, It went off. Checked the oil level and it was low. Refilled it and the oil leak appeared. As the engine was pretty clean, I could see that the oil came from the head gasket, so the problem must be there. The leak doesn't appear running low on oil, but onde the required amount of oil is on the engine, the gasket can't cope with the right amount of oil pressure. Am I right?
As Terry suggested, the problem can be that I didn't torque the HD APE studs enough, I gave them the standard torque.

In this reply you mentioned the the K7 bolts w/no Phillips slots, just to be sure, you only used the F2 head, cylinders and cases correct? No K7 motor parts stuck in the F2 motor build? (As the oil galleries are different on K model motors)

[mazingerzeca]

Sorry, I wrote K7, I meant F2. The engine is a complete F2 engine, no parts from K7 engine on it. I use to call the bike, "K7", hence the mistake.

[PeWe]

The max oil levels will happen after 20- 30 minutes on my bikes. It can be a little bit higher after crusing above 160kmh.

But if you got lack of oil when riding, no earlier idle on sidestand. Thats different.

See photo if my bikes. If I start  and let bike idle as a warm-up on sidestand, low oil will happen, even if oil level was OK before. Pump valve is closed not letting oil into case when off over night.

I always let it idle for a short warm up when I sit on the bike before take off. That helps, no issue with oil level that becomes lower when cold. Ok after a ride.

This concerned me a lot after the first oil warning and I saw the low oil level in tank.

My blue bike's original pump always let oil to flow into engine over night.
No oil issue at next start. No thick studs back then. Maybe they are involved.
My bikes are K2, K6. Different oil tank but the engine oil system same.

[newday777]

You mentioned you had "Flattened head surface". Did a shop deck the head? If so, did you shorten the dowel pins to make up the decked surfaced amount? Otherwise a leak could happen there.....
You used the Honda head gasket for the F2(bigger oil return holes than K and F1 headgaskets) or aftermarket headgasket?

[mazingerzeca]

Yes, I had the head decked on a shop. OMG, I didn't check if the dowel pins lenght allowed the head to fully seat. Yes, I used the F2 head gasket. I think that a top end overhaul is on the way...

[Jerry Rxman Griffin aka MuthaF'er]

Have you checked the screen on your oil pump to ensure it is clear of debris?

[mazingerzeca]

Yes, I have, and it is clean.

[scottly]

I made the test you suggested on my bike. I took off the valve tappet cover and there was no oil there, so it seems that it drains well to the oil sump.

Was this test done when the engine was running and low oil pressure indicated?