Topic: Oil jets

[Shane jamieson]

Hi Guys.
I have a 750k2 that I brought a year or so ago and have had issues with it only running on three cylinders and an oil leak.i did a compression test resulting in 150+ psi in all four. I have since pulled the engine and every thing checks out so I am leaning towards a carb issue. The oil issue appears to have been the tappet gasket.

My question is when I removed the cam journals the oil jets were missing, are these necessary. I have noticed the oil pressure light came on when the bike is hot at idle. With the restricters missing would they cause this to happen.

Regards
Shane

[69cb750]

The oil jets reduce the oil flow to the head and increase the oil flow to the crank, Honda designed it this way, I would replace them.

[bryanj]

Yes it would drop pressure at the crank and oil light switch

[newday777]

Hi Guys.
I have a 750k2 that I brought a year or so ago and have had issues with it only running on three cylinders and an oil leak.i did a compression test resulting in 150+ psi in all four. I have since pulled the engine and every thing checks out so I am leaning towards a carb issue. The oil issue appears to have been the tappet gasket.

My question is when I removed the cam journals the oil jets were missing, are these necessary. I have noticed the oil pressure light came on when the bike is hot at idle. With the restricters missing would they cause this to happen.

Regards
Shane

Welcome to the forum Shane
Did you remove the oil restrictors?
The answer is yes they are needed and will reduce the oil pressure to the bottom end as well as add more oil to the cam area without them.
The usual cause of oil leaks at the top end is shrunken rubber pucks covering the head bolts/nuts in the open fin area in the upper head fins. The rubber shrinks and hardens from age and lack of use, then it doesn't swell back up readily as it should.

[RAFster122s]

The pucks available from the dealer and if included in a head gasket/gasket set are typically too thin and Parts-N-More carries the correct thickness pucks.
The others even if they seal for a little while they quickly start leaking

[HondaMan]

If you need some oil jets, PM me.

I once rebuilt a 750 that had just been ridden from Michigan, thru Colorado (to visit me) and on to California, after which the engine was pulled and sent to me for 100% rebuild (he plans to keep it a LONG time). When I took it apart, the oil jets were missing, like yours! The crank bearings were OK for clearance (he used correct oils, and so did the PO) and went back in, unscathed. The top end had a tendency to weep oil, though, because there was LOTS more oil being pumped up there than Honda intended. A normal "increase" in oil flow for those [missing] oil jets is like making them 0.004"-0.008" larger holes (for racing requirements): removing them altogether is a bit much!

[Shane jamieson]

Hi Guys, thanks very much for the replies, I really appreciate it.

So I have sorted the oil leak. It was just the gasket not seating properly.

I did not remove the oil jets as this is the first time I have had the engine out of the bike and part.
I had another look at the oil galleries were the jets sit and then the
 Mating side of the cam holder.

There appears to be small jets just below where the inlet rocker rods sit.  Photo attached. Are these jets used in conjunction with the missing larger jets you all said should be there or is the head I have of an older engine and they just use the jets on the cam holder.

Hondaman, I will definitely need two if it turns out I need them.


Thanks guys.

[M 750K6]

I sealed the pucks in my gasket kit, using high temp gasket sealant. Not too much though.

[newday777]

Hi Guys, thanks very much for the replies, I really appreciate it.

So I have sorted the oil leak. It was just the gasket not seating properly.

I did not remove the oil jets as this is the first time I have had the engine out of the bike and part.
I had another look at the oil galleries were the jets sit and then the
 Mating side of the cam holder.

There appears to be small jets just below where the inlet rocker rods sit.  Photo attached. Are these jets used in conjunction with the missing larger jets you all said should be there or is the head I have of an older engine and they just use the jets on the cam holder.

Hondaman, I will definitely need two if it turns out I need them.


Thanks guys.

Those holes in the cam towers are not jets. Oil ports for oil flow to lube the parts.
The oil orifices are located in the head.

What oil were you using in your motor? Hopefully not 10w40. These motors need 20w50 in heat above 70°F(21c)

[HondaMan]

The oil jets are #6 in the head diagram here:
https://www.southsoundhonda.com/--xpartsstream#/Honda_Powersports/CB750KA_(76)_750_FOUR%2c_JPN%2c_VIN%23_CB750-2540001_TO_CB750-2575894/CYLINDER_HEAD/b3d05c73-22e7-4620-b018-132301d96b6e/58a86ed9-04d7-422c-b0e8-d2356946658a/y

They are located underneath the cam bearing housing(s), near the cam chain's tunnel, above cylinders 2 & 3. There is an O-ring around each one, and another O-ring of similar size (in K2 and later engines) on the opposite side (cylinders 1 & 4). These O-rings are very important: don't lose them! I have them, too, if you need some.

[HondaMan]

Jets and new O-rings enroute. Replace all 4 O-rings with the new ones I sent.

[Shane jamieson]

Thanks Hondaman for the parts. I would also like to thank all who responded, I appreciate your views very much.

I will keep you posted with the update when I have the engine back in the frame.

Regards all,

Shane.

[PeWe]

The manual I got with my CB750 say >+15"C as the point where 20W-50 should be used.  Lower 10W-40 which will never happen.

My garage is minimum 21-22*C

[bryanj]

In UK we always used 10w40 no matter what temp

[RAFster122s]

In UK we always used 10w40 no matter what temp

Yes, but 75F is a heat wave in the UK, lots of nights here in Tucson it only goes down to 80, last night it rained quite a bit so it reached 78. 2 days ago it only reached 84F overnight 
So, your average daily high temp is not in the same ballpark and the 10w40 is a logical choice and it provides plenty of protection for the warmer temps you will see. It will be November before our daily high temp is in the mid 70s. Now our daily high is averaging 100-105f

So, definitely do not visit the desert SW if you are living in England unless it is winter time...
You would not enjoy your visit if you are suffering from heat exhaustion...

Here 20w50 is a year round oil on all but about a 2-3 week period

[PeWe]

The Arizona desert hot temperature a reason to use 20W-60, right?

[RAFster122s]

Synthetic oil and water cooled bikes in summer

[bryanj]

Dont forget to replace and reseal the rubber pucks under the cam towers

[Shane jamieson]

Well guys I have updates.

I put the new oil jets in the head, valve seals and gaskets and put the whole bike back together. No oil leaks and my oil pressure light now stays off, even while syncing the cards. I went for a first decent ride last weekend and the oil light ever came on once, so I would say that issue is fixed. Bike still could be running a bit rich though, plugs are a bit black. I set the floats at the recommendation height, 22mm I think but it was still running rich. I then used the clean tube method on the bottom of the bowls which showed the fuel up to the base the carb. I then dropped the fuel about 1/4” from the top of the bowl and it ran better. This is currently where it is set when I rode it on Sunday. I have yet to do a couple of pulls and check the plugs but at a guess, I think it maybe just the idle circuit. For the record, I am running 10w40 all year round.

Cheers
Shane.

[turkey4me]

Another CB back on the road!  Nicely done Shane

[HondaMan]

Well guys I have updates.

I put the new oil jets in the head, valve seals and gaskets and put the whole bike back together. No oil leaks and my oil pressure light now stays off, even while syncing the cards. I went for a first decent ride last weekend and the oil light ever came on once, so I would say that issue is fixed. Bike still could be running a bit rich though, plugs are a bit black. I set the floats at the recommendation height, 22mm I think but it was still running rich. I then used the clean tube method on the bottom of the bowls which showed the fuel up to the base the carb. I then dropped the fuel about 1/4” from the top of the bowl and it ran better. This is currently where it is set when I rode it on Sunday. I have yet to do a couple of pulls and check the plugs but at a guess, I think it maybe just the idle circuit. For the record, I am running 10w40 all year round.

Cheers
Shane.

22mm is mighty deep in the 657b series carbs, so yeah, that will be quite rich(!). Normal is 26mm, and I run 26/25mm (the 35mm one being the one furthest from the kickstand side) in most bikes, or 25/24mm in my own.

Don't run the 10w40 in the hot weather. It is real hard on the rockers, cam, and cam bearings for the cam journals. Use about 2 ounces of ZDDP in it, too: you'll find it shifts far better, warms up more quickly and idles smoother, not to mention running quieter. The zinc was removed from all our motor oils in the 1990s to preserve catalytic convertors in cars and such things.

I use (and recommend) this version of the ZDDP:
https://www.ebay.com/itm/173985022237?_skw=ZDDP+plus&epid=1632536415&itmmeta=01JB0W0DS7M463D9BGBKNKSGPA&hash=item288250c11d:g:ClUAAOSw7CBdQ0gs&itmprp=enc%3AAQAJAAAA0HoV3kP08IDx%2BKZ9MfhVJKmX4XFTIa4Z5ybmcBjFfIrSUx%2FEssBVL6eSzld2pdcm3RObJYtZYbn3oeteAqA8yUkMK8jCLNfzCLHssi6zFk9SggnwNiFjOmIjiSiL1cpZl1eQBX5vX6aZ3tKAroPQTCdVM49XP2pg7hy2n%2B29dErmv7IUMg%2FHIe8MGnzI%2BJGqZvrY3UxY9lNGnt9eTI9I7pVOIlDsi0YTP%2FeqellpUc8Gv5br%2BWwvS8kxr5ooHdODgW5%2F77ddTUkk5PrP8GiNjFc%3D%7Ctkp%3ABk9SR-bcgZzYZA

I run 1500-2000 mile oil changes, too, using this and the Bel-Ray 20w50 EXL Mineral oils. Smoothes the bike a lot.

[rotortiller]

In UK we always used 10w40 no matter what temp

People see something out of place, create a scenario and run with it.

Same here for Canada as all the manuals recommended it as a general all round oil. Likely a misprint in that one manual posted by pewe, if you go to the library here for SOHCs you will find the lighter weight  10w40 oil general use oil as recommended by Honda. I run it all summer, some days are 30c and have 60,000 miles on the bike with the engine never opened. 20w50 will not hurt anything, it's just not the recommended general use oil in most all of the respective Honda manuals. Suzuki GS750 like the Honda CB750SOHC recommend 10w40 as general use all temperatures. Some manufacturers of this time period recommend 10w40, 20w50 etc. for your personal choice using CDF. If you go to the 1979 DOHC750 which is higher output, the general recommendation of 10w40 continues. Feel safe and confident in using 10W40 or 20W50.

[Don R]

 I have an early head for my diecast motor that has the o ring around the oil jet but doesn't have the machined spot for a second o ring for the cam towers. I'm told it is serial #400 or lower. It's on a formerly sandcast motor but now has a blank replacement case.

[jonda500]

+1 - Last century I used 10-40 oil in my honda for over a decade as that is what it said on the dipstick (and it gets bloody hot here!) - I think it's unlikely that you could hurt a Honda by running 10-40 oil!
John

[HondaMan]

I have an early head for my diecast motor that has the o ring around the oil jet but doesn't have the machined spot for a second o ring for the cam towers. I'm told it is serial #400 or lower. It's on a formerly sandcast motor but now has a blank replacement case.

The earliest cam bearing/rocker towers only had an "inny" hole for the oil, so there was a "left" and a "right" cam bearing. Somewhere late in the sandcast they made the cam bearing interchangeable as for the sides. My Honda mentor Jim had the uni-directional ones, which was how he (and I) found it out. It's not hard to modify the bearing, but then there's the need for the extra O-ring...