Topic: Venting tappet covers?

[Korven]

Anyone seen these tappet covers listed below. Do they provide any extra venting or are they just for bling (don't see how hoses everywhere is bling though) haven't seen them onto any bike so far. Cmsnl has them listed

[slikwilli420]

For what bike? I dont see any advantage on our fours since at least the 750 has a vent at the cam cover which is more than sufficient. On the other hand, you could pump oil into those to keep the valves in oil, but likely no necessary. Voxonda set his endurance bike up with small jets to put oil on the rocker shafts/cam lobes via a set of lines coming from an oil galley.

[MRieck]

I saw those on the CMSNL site....Better than the homemade pieces I've seen.

[Cb750 Racer]

I'm interested in a few. Anyone have a link?

[PeWe]

Always parts to order!   I have just ordered an oil pressure gauge kit for my k2.
The breather cap look really good!
https://www.cmsnl.com/honda-cb750k5-four-1975-usa_model483/cap-tappet-breather-non_12361rrp020/#.XGsmwOj0nIU

[bwaller]

Make sure you don't vent them in front of the rear tire. 

[seanbarney41]

But why?

[scottly]

Oil will be flung up off the tops of the valves, directly up into the vent holes. Unless there is some sort of air/oil separator, or a decent amount of vertical tubing, oil will make it's way out of the ends of the vent tubes. If you have so much pressure in the engine that extra venting is required, it's likely due to poor ring sealing.

[seanbarney41]

that is what I meant...seems the worst possible location for a vent/s

[scottly]

 

[754]

that is what I meant...seems the worst possible location for a vent/s

It would be great if your oil jet is plugged up, giver a shot of oil every few minutes..

[Korven]

Wouldn't there be a risk to fill the pockets where the rocker arms are fully up with oil? Don't know how they splash the oil around, but might give some movement resistance? There is a small gap between the cover and where the cam lies.

[turboguzzi]

i've seen those on twin cyl (CB350) and single cyl racers which tend more to build up pressure downstairs. in my supermono I had to vent from a similar location because the original breather at crankcase level was collecting too much oil mist. At least in my case, the valve tops didnt fling any oil, actually the tappet cover vent collected much less oil than the original down low location.
As someone else said here, not really necessary on a four, unless you have ring sealing issues. all my four cyl racers do just fine with the stock breather location.

[flatlander]

says in the description under pewe's link:
High qualityTappet Cap with breather. Excellent for high performance Cub engines, especially when used hard.

cub engine is a small single cyl - totally different from our fours. no idea why CMSNL lists them for the 750. i guess you could technically fit them but what's the point?

[MRieck]

 I think they would help venting a 750 when you start increasing the bore 10 or 11mm and stroke by 5mm.

[gschuld]

I think they would help venting a 750 when you start increasing the bore 10 or 11mm and stroke by 5mm.

Might still need a bit of a baffle of some sort to discourage splash oil from getting sucked out I’d think.  Wouldn’t an increased volume vacuum port at the factory location be a better option considering it has the baffle thing covered by design already?

George

[754]

 The tapped cover fits about 250 applications  some not valvecovers
And many many models.
 I suspected it may be often used on the laydown singles  i think I saw them there before.

[flatlander]

exactly. laydown single -  that's the cub engine they refer to in the description.

[strynboen]

think it are a return for a oilcooler..some 1 cyll engines take oil aut from the side of the head..lead it throughg a cooler and return it in the adjusting cap

[PeWe]

I think they would help venting a 750 when you start increasing the bore 10 or 11mm and stroke by 5mm.

We discussed extra venting in a thread when my engine had some case pressure weeping oil around oil filter cover. 71.25mm pistons pump more air
I should have done it earlier with my 836 if I knew.
It was enough to add the vent thru the clutch cover as you have Mike.
 I think Sam Green mentioned extra top vent thru the tappet covers, IN 2&3.
This solution is really nice then .

[Don R]

 I have a rocker cover with an extra vent and barbed fitting in it. I don't remember finding a big engine under it though.

[scottly]

IIRC, the vent nipple on the cam cover is not an open tube on the inside end, it's closed on the end with a rather small opening on the bottom. This small opening may be enough to relieve the blow-by for smaller bores, but 5% leakage from 61mm bores would be much less volume than 5% leakage from 71mm bores??

[Bill/BentON Racing]

What Mike said......

[Sam Green Racing]

I think they would help venting a 750 when you start increasing the bore 10 or 11mm and stroke by 5mm.

We discussed extra venting in a thread when my engine had some case pressure weeping oil around oil filter cover. 71.25mm pistons pump more air
I should have done it earlier with my 836 if I knew.
It was enough to add the vent thru the clutch cover as you have Mike.
 I think Sam Green mentioned extra top vent thru the tappet covers, IN 2&3.
This solution is really nice then .

To be honest PeWe, I don't think the extra breathers are necessary and the top breather from the cam box is quite adequate.
I remember the original thread well and fitted the extra breathers on numbers 2 and 3 tappet covers of my Auto in the States just to be safe.
In the UK, if you are racing a bike, all breathers must terminate into a catch can and the same was done on my Auto in the States.
When I got involved with the CB750 in the first place, the 836 that I built in the UK had a catch can from just the top breather and the residue in it was monitored after every event. The same was done with the 836 in the USA and even when it was taken out to 915, results were just the same.
When we talk about the pumping action of the pistons creating pressure, is this really true.
When two pistons go down, they create pressure below them (positive pressure) but at the same time, the other two pistons are going up cancelling this out (negative pressure).
Excessive pressure in a motor can only be down to 2 things if it is set up correctly. The first is bore wear and the second is the extra heat generated by the bigger motor and I think like Mike said, this is only in really big motors.

Sam.

[PeWe]

Extra vent thru clutch cover did it as others told me. Pity I was not aware of this in the 80's when abusing the streets and my bike with 836
http://forums.sohc4.net/index.php/topic,172703.msg2010515.html#msg2010515