Sourcing Roller Rockers

[CLEAH]

Enjoy your rebuild and I am happy to leave this here or continue, but I have a war to fight.

Don

OK, I'm going to cast a vote for not continuing with the grammar and spelling lessons!

 

[HealeyDave]

From my limited reading - roller rockers can have needle bearings, or just journal type bearings. In any event, the purpose is to allow higher rocker ratios, with effectively increases valve lift for a given cam profile, without generating very high frictional side loads on the pushrods, and parasitic loss due to friction. The result is 1) better engine breathing (engines are just air pumps) and 2) much less rocker arm friction, which equals more power.
On the subject of the bearing not rotating completely and potentially causing bearings to 'brinell': I don't think the motion of the bearing is exactly conjugate with the motion of the pushrod. They don't rotate through the same angle back and forth constantly. There is some lost motion due to friction between the 2, and so the bearing does constantly rotate so as not to 'brinell'.
The benefits are real - but mostly for high performance and racing applications. And of course there's the added cost. So, if you race vintage for example, and roller rockers are allowed, and you have the coin - then the benefit could be well worth the investment. For a Sunday driver - maybe not so much. As another poster mentioned - improved coatings can really help with reducing friction and wear on a more standard engine.

Driveline u-joints are a separate issue - one I know more about. Ideally, a propshaft with u-joints (as opposed to consant velocity (CV) type joints) is supposed to be set up with more than zero degrees of angle, and less than about 1 degree. That's total included angle (both ends of the prop). This allows the u-joint bearings to constantly rotate, which reduces the 'brinelling' of the bearings, which helps with bearing life. These recommended angle set-ups are 'static' - there is always dynamic motion of the prop due to suspension motion, but that is transient in nature. More than about 1 degree angle in the propshaft and you get into wear issues as well as vibration issues. Yes, the jacked up trucks do have severe angles and bearing life is significantly reduced. Or, they run a different type of bearing set-up that can handle the angle. Those guys mostly know all that.
The 2 per rev vibration generated by joints working at higher angles can cause multiple problems other than just operator discomfort. The vibration is a forcing function that can excite many resonant vibration modes in the driveline and vehicle body - which can result in accelerated structural failures. U-joint bearing failures can be the least expensive of the problems.
my 2 cents.

 

[jcsb]

Don,
First I accept your apology. On the subject for spirited debate, I would say that this post had nothing to do with a debate. If you had read the original post then you would see I wasn't asking for opinions. I even said that I didn't need the rockers, but wanted to see if there was a different source. At some point it got off theme and became unproductive.

No, I didn't miss the point of your original comment. I said that there was a better chance that u-joints would fail due to maintaining a good seal and keeping the grease free of debris. There are many thrust bearing situations in which the roller bearing is put under static load with no failure. As an example the thrust bearing in the suspension of my Austin Healey was replaced from a solid thrust bearing with a roller bearing and so for it's holding up fine.

With roller rockers there is an increase in ratio of movement of the arm. This is done by moving the pivoting center point back towards the cam and pushrods, thus increase the angular movement.

I will pass your concerns on to the many manufacturers of these products so that they can take them off the market.

John

 

[jcsb]

From my limited reading - roller rockers can have needle bearings, or just journal type bearings. In any event, the purpose is to allow higher rocker ratios, with effectively increases valve lift for a given cam profile, without generating very high frictional side loads on the pushrods, and parasitic loss due to friction. The result is 1) better engine breathing (engines are just air pumps) and 2) much less rocker arm friction, which equals more power.
On the subject of the bearing not rotating completely and potentially causing bearings to 'brinell': I don't think the motion of the bearing is exactly conjugate with the motion of the pushrod. They don't rotate through the same angle back and forth constantly. There is some lost motion due to friction between the 2, and so the bearing does constantly rotate so as not to 'brinell'.
The benefits are real - but mostly for high performance and racing applications. And of course there's the added cost. So, if you race vintage for example, and roller rockers are allowed, and you have the coin - then the benefit could be well worth the investment. For a Sunday driver - maybe not so much. As another poster mentioned - improved coatings can really help with reducing friction and wear on a more standard engine.

Driveline u-joints are a separate issue - one I know more about. Ideally, a propshaft with u-joints (as opposed to consant velocity (CV) type joints) is supposed to be set up with more than zero degrees of angle, and less than about 1 degree. That's total included angle (both ends of the prop). This allows the u-joint bearings to constantly rotate, which reduces the 'brinelling' of the bearings, which helps with bearing life. These recommended angle set-ups are 'static' - there is always dynamic motion of the prop due to suspension motion, but that is transient in nature. More than about 1 degree angle in the propshaft and you get into wear issues as well as vibration issues. Yes, the jacked up trucks do have severe angles and bearing life is significantly reduced. Or, they run a different type of bearing set-up that can handle the angle. Those guys mostly know all that.
The 2 per rev vibration generated by joints working at higher angles can cause multiple problems other than just operator discomfort. The vibration is a forcing function that can excite many resonant vibration modes in the driveline and vehicle body - which can result in accelerated structural failures. U-joint bearing failures can be the least expensive of the problems.
my 2 cents.

Thanks for your input Dave. I really didn't start the post to get into this part of the discussion, but I do appreciate your remarks. Have you seen how The Healey Factory are doing their roller rockers? First time I've seen it implemented as part of the valve cover.

John