Topic: Cylinder head oil return

[Ageoldstrings]

Having now pulled a couple of motors with badly scored cam bearings I’m thinking about what can help lubrication in my new road race engine build.

Plugging the oil return holes next to the valve springs and allowing oil to build up until it finds its way back via the cam chain tunnel is an idea I’ve heard before - has anyone tried this? 

[grcamna2]

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[PeWe]

If a CB750:
Maybe the oil feed holes are plugged or partly plugged?
No need to use sealer anywhere close the oil feed.

From lower case up thru cylinder and head oil feed holes.
Finally thru the oil restrictors in head + cam holders.

Next if wrong oil is used, viscosity and type, too seldom changed.

If wrong oil is used, valve guides can get shorter life too.

I have not seen any bad wear on my cam with holders despite high lifting cam and harder pressing race springs.

I have seen those parts rather often due to other things to fix or improve.

[Ageoldstrings]

Yes I understand all of those things. I’m wondering if plugging the returns can be of benefit when everything else is correct also…

[newday777]

Having now pulled a couple of motors with badly scored cam bearings I’m thinking about what can help lubrication in my new road race engine build.

Plugging the oil return holes next to the valve springs and allowing oil to build up until it finds its way back via the cam chain tunnel is an idea I’ve heard before - has anyone tried this?

Welcome to the forum Ageoldstrings
When starting a new topic, please include what bike you are asking for information on.
I've not heard of plugging the return holes.
The common cause of worn cam bearing surface is supply restrictors being plugged from debris in the oil restrictors to the head. 
Or of weak oil pump pressure from worn parts.
Do you have the bigger heavy duty cylinder head studs? They will slow the oil return down from the head.

Introduce yourself and your bike in the new members section
http://forums.sohc4.net/index.php/board,58.0.html

[madmtnmotors]

Sounds quixotic to me. Oil return does not destroy cam tower bearing surfaces, oil starvation on the supply side dooms these cam bearing surfaces. Obstructions in the oil feed metering jets being the #1 culprit, often from the indiscriminate use of gasket sealers (especially silicone) throughout the engine. I too have seen more than one of these types of failures. So keep it clean during reassembly, put away the silicone, and build it right.

EZPZ

[PeWe]

It was one guy on this forum that wrote about a mistake when painting the cases.
The cyl studs were not masked so they got paint.
That paint later clogged the oil orifices in head when engine was running. Cam, holders and rockers suffered very hard.

Important to cover the 2 oil feed holes when taking things apart. Piston dome/chamber soot can fall inside. Gasket material too.

Here during an operation cleaning domes, all holes covered. Guides were not sunken enough for the 125-75 cam so it sucked oil thru the inlet guides when valve grooves for keepers dove into the guide seals.

Head fixed, pistons cleaned.
I used a vacuum cleaner with thin hose taped on to suck out eventual debris in case holes for oil flow up. Sprayed WD-40 in there and sucked again just for sure.



The RCS  base gasket had earlier minor oil weep.  (Rubber Coated Steel)

I used a very thin layer of high temp silicone on the base gaskets both sides. I was really careful around oil feed holes. I knew were it weaped.

I waited to assemble until silicone had cured to avoid sticky silicone in wrong hole.
The 2 o-rings keep silicone outside.
That was around 18.000 km ago, still spinning and screaming in the right way

An RCS base gasket can be reused over and over again with help of very thin layer of high temp silicone. Like making surface dirty with oily fingers of old oil.

I wonder about next build. I consider to reinforce the viton layer with silicone direct. Not fun when oil weeps. Fix that means lots of work.
Not fun when everything is properly timed and adjusted.

[PeWe]

One more thing about oil feed to head/cam.
Heavy duty cylinder studs are 8mm in diameter.
Stock studs 6mm where oil flows, plenty of room for oil up thru head.
Here a head where the 2 oil feed holes were around 8.5mm.
Not much left for oil to flow with HD studs.

So I drilled the 2 holes with 9.5mm drill. Oil orifices removed before.
All other stud holes updated with a 9.0mm drill all the way thru head from gasket side.



My ported K2 head, not on photo, has early oil orifices (shower nozzle model) they got the center hole updated with an 1.0mm drill, plus a few of the others on the shower side.

(I had another head where the nuts went deeper into head, alu formed around studs so I had to bang head off with a heavy nylon hammmer on exhaust spigots fastened for the job. So a little wider holes can help.)

Some MLS head gaskets with early small oil return holes might slow down the oil return when holes are 8.5mm.

Rev a cold engine with tight oil feed, up and down might get issues when oil is thicker.

[HondaMan]

Maybe some understanding of how the 750 works (I'm supposing you have a 750?) up top will help?

The oil is fed thru the 0.0375" metering holes in the 2 oil jets (if it is a K2 or later CB750 engine) and this flow is divided into 4 outlets in the cam bearings. each of which is 0.020". The inner 2 can bearings thus get more oil than the outer 2, and the inner cam lobes for cylinders 2-3 get more than the 1-4 sides.

The metering hole in the oil jet can be opened up for more flow IF the oil pump is flowing in good condition and providing full flow and pressure: for this you may need to replace the O-rings inside, the metering seals and the shaft seal, and make sure the rotors are good, insie the pump. It should provide 60 PSI pressure at the main journal behind the cylinders at cold cranking speed (sans sparkplugs) with 20w50 oil, and never use detergent oils in this engine, especially for high-RPM use. Use something like Bel-Ray's EXL Mineral 20w50 or the Golden Spectro in similar weight. Specifically avoid oils labelled "for V-Twin engines".

I once rebuilt a 750K6 after it had run from Michigan to California in Fall weather, only because its new owner had flown to MI to get it, and was making it into a show bike after getting it home to CA. When I got the engine, it had NO OIL JETS at all in the head, The top end was in gorgeous condition, too, at 18k-ish miles. So, the metering holes in the cam bearings themselves were sufficient to meter the oil: the bottom end bearings were likewise in pristine condition, with the loosest one just touching 0.0021" clearance. The oil pump was in perfect condition, too, having been refurbished sometime before I got the engine for the build.

[PeWe]

Do not forget all 4 o-rings under the 2 cam holders.

I remember I had thoughts about the outer o-rings to the flat head surface first time I had engine apart  in early 80's.
"Best to do as Honda did" was my thought then.

Understood later the importance of keeping the ends tight not loosing pressure with less oil squirting out thru the holes were the valve train need it.

Thicker o-rings not better.
Photo show a viton 2.0 x 6.0 mm o-ring written in an o-ring chart to replace stock nitrile 1.9 mm thick o-ring. I was lucky to not get the oil blocked that time.

After this I used Honda o-rings I had plus ordered a 50 pack of nitrile 1.9 x 5.8mm
This for later head with the slimmer orifice.
Use stock size.
91305-323-000 1.9x5.8mm
Superseded by
91318-ME5-003 O-ring, 5.6x1.9
That size have more room for swelling without cracking.

Good idea to verify the stock sized o-ring has a little stick up over the surface.
I check with a feeler gauge.

I think that a nitrile should have compressed without cracking in small pieces.

That o-ring had not sit long.

[Tracksnblades1]

Good picture PEWE.

Oring overfill/extrusion is the terminology. Compressing it until the rubber “flows”.

Static seal vs dynamic vs combination oring seal..

There are ASME and ISO standards so one doesn’t have to reinvent the wheel for the correct oring uses, machining clearances, durometer/shores, pressure ranges, surface finishes, compression, etc..etc..

Most machine shop that routinely machine internal, external, face, oring grooves should be able to help you…

There’s old posts  with Parker oring links…

https://promo.parker.com/promotionsite/oring%2Dehandbook/us/en/ehome/Gland%2DOverfill

https://promo.parker.com/promotionsite/oring%2Dehandbook/us/en/ehome/Extrusion%2Dand%2DNibbling

[johno]

Pewe, your a bloody legend 
I think its about time that Honda Japan gave you a ring and give you a well paid job on their GP team. They are fresh out of ideas and need someone like you to inspire them 👍🏍🏁💰
Thanks for your input Pewe,
cheers Johno

[johno]

Oh I forgot to say, touching on what Honda man said about the the 2 metering jets and oil orifices there after ! I agree that the post jet orifices are the restrictors, the 2 "metering jets" or rock stoppers as I call them are in fact a safety feature by having the multiple holes to prevent a single hole from stopping oil flow. They are only there to protect the smaller orifices in the cam bearings etc from receiving small pieces of crap, kind of a harry half ars#d way of catching some foreign floats.
I have tried to improve them by replacing the jets with a fine mesh, I never did find out if it made any difference though as I never got to rebuild the engine to inspect, so don't know,
Funny isn't it, since 1969 so many people in the world have looked at the sohc engine to improve it and as a stock engine it is almost perfect but to turn it into a 100hp beast it opens up a can of worms.

[PeWe]

Thanks for the nice words guys!

Good threads about o-rings that show the problem I got.

It would be fine to be a part of a GP team. Documenting small as big issues to not let it happen again. RCA team. (Root Cause Analyze).
I have worked with that for many years, still doing a little, mostly tech support but with Industrial robots.

When o-rings are up.
Hondaman has notified the issue with the 2 o-rings for oil feed vs head gasket thickness.
Stock o-rings for old stock gaskets of 0.8mm thick.
Later aftermarket gaskets 1.0mm and even 1.2mm.
That will make the o-rings too thin, can leak oil when o-ring compression is too small.
Grooves in cylinder + gasket thickness vs height of o-ring.

I had to dive into it and could verify what Hondaman wrote to be correct.
Found compression ratio about 20-30% .

http://forums.sohc4.net/index.php/topic,153549.msg2203559.html#msg2203559

[Ageoldstrings]

Thank you for all the information in these posts! This really is a great resource.

Consensus is no benefit to the cam bearings and not necessary
 

[HondaMan]

Oh I forgot to say, touching on what Honda man said about the the 2 metering jets and oil orifices there after ! I agree that the post jet orifices are the restrictors, the 2 "metering jets" or rock stoppers as I call them are in fact a safety feature by having the multiple holes to prevent a single hole from stopping oil flow.

So right you are! I just rebuilt one of the sandcasts, and along the way I discovered the mysterious source of those 'rocks' that destroyed the cams and rockers on so many of the early engines: the main oil journal (behind the cylinders) was formed during casting by inserting mold rods from each side, half the width of the engine each, to meet in the middle, which caused a slight mold-edge 'flash' to form where they met. These early engines had just a single oil hole to meter the oil into the cam bearing on each side, and they frequently plugged and ruined the top end. Honda warranteed them all without a word of objection when I was working with them in those days, and we always thought that strange since they always double-checked any other warranty issues on the other bikes. Their first solution, of course, was massive overkill with the "dome-style" oil jet assemblies, but they are very effective. After they changed the molds to have a single rod all the way across the back of the engine instead (K0 engines) these casting flash issues went away, and they became confident enough by the K2 engine (somewhere around 12/71 or so) to reduce those oil filter-jets to just 7 strainer holes. These work well unless someone uses too much goop in the gaskets, then they get plugged, too - but, that's not Honda's fault!

[johno]

so enough said on top end oil starving, now for my two bobs worth  Also last paragraph will be on original question blanking oil drain holes.

Think it was Pe We Per who raised the issue of the 8mm studs and the MLS gaskets hole size. Thanks per after your post I done some checking.
The early style heads and barrels had stud hole sizes that varied from 8.5mm to 10mm. The later style heads barrels were mostly 10mm.
OIL UP
When considering oil flow to the top end be aware the space around the studs must be same or better than the area of the 4mm oil gallery that supplies the oil from stud hole to restrictor.  (4mm hole has total area of 16.7mm2)
Example of areas in square mm;
8mm stud area = 66.7mm2
9mm hole area = 82.5mm2 minus stud 66.7mm2 = 15.8mm2
9.5mm hole area = 94mm2 minus stud 66.7mm2 =27.3mm2
10mm hole area = 104mm2.
11mm hole area = 126mm2
 The stud and stud hole and gasket hole must have 16.7mm2 area clearance or more to not restrict flow ( so 9mm hole restricts).        Note slight increase in diamiter's makes big difference to area.
Note when measuring and drilling the two main oil feed stud holes in the cylinder head the hole will measure up 8mm on the top of the head but 10mm on the bottom of head. This is because the oil gallery from stud hole to restrictor hole leaves stud hole at an angle about 30mm under top of head , Honda leave the STUD hole smaller on top to help support the head nuts.
OIL DOWN
The oil drain holes in the head from valve seat area to stud hole are 7mm diam. or 51mm2 area so the stud to hole area and gasket to stud area need to match or better the 7mm drain hole of 51mm2.  Using the above numbers the minimum drain stud hole diam would be 10.5mm2.
Note the barrel and head stud drain holes vary in diameter on different models and some are tapered so check carefully.
BLOCKING OFF OIL DRAIN HOLES IN HEAD.
You must be crazy to add xtra oil into the top end by doing that 
However if on a race bike the inlet ports have been opened up on the inside of the turn and brake into the stud hole then it has to be sleeved and the 7mm oil drain down hole from valve seat area is plugged to prevent vacuum leaking past sleeve and sucking in oil. Then a channel is milled across to the next cylinder valve seat area to share the 7mm diam. 51mm2 oil down hole. That about right Mike ?  That means the gasket to stud , stud to hole etc must be capable of exceeding at least one hole 51mm2 prefer two @ 102mm2. So far the best Ive done is 11mm hole = 126mm2 - stud 66.7mm2 =59.3mm2 = 8.3mm2 more than one 7mm hole.
So its possible to pool around the valve seat area on the two valves. However so far it has been OK and I have checked the exhaust ports for oil on 3 occasions as the 5mm kit has lower guides and seals but NO oil in port or showing out of exhaust.👍
If using MLS gaskets, the early type small holes need to be enlarged to match the stud hole size, don't drill, don't grind with stones use a 3/8 carbide rotary burr as cleaner cut and easy to clean between layers with air only.  OR use later big hole gaskets.
ciao Johno

[HondaMan]

I think for the original OP: just drill the metering holes a bit in the oil jets. They came is sizes from 0.0350" to 0.0375" from Honda, except for the sandcasts with the hand-drilled 0.040" (but much too long) ports.

If I were making a high-RPM beast of these for track use now, I think I would drill them to 0.044" or maybe 0.047" and make sure the [good] oil pump's shaft seal (between the chambers) was fresh and new, and the bypass oil regulator spring was shimmed about 0.040" to 0.080". This should release about 10%-15% more oil into the top end, all else being equal. The famous minicar racers in IL (mad machinists, I called them) who used a different oil pump for their 14k RPM hotrod versions of these engines opened up the oil jets, though they wouldn't tell me how far: their oil pumps delivered lots more volume than ours, though. I saw one of the heads uncovered once (maybe twice) and I know the metering hole was noticeably bigger, but I'm a bad guesser at that sort of thing, accuracy-wise.