different valvetrain question
- Thread starter Asa
- Start date
Possible but very expensive. You need to bore the cam bearing bolsters in the block oversize to accomodate part of the difference in size and have a cam ground with the jounals undersized to suit the ID of the bearings. The standard hardening process for the journals might not be enough since the rollers would ride directly on the cam with no separate inner race. In the end you're going to gain what? There's not a whole lot of frictional load in the cam bearings so even if you reduce it by 90% it's not much of a gain. It might make sense in a race engine that gets major overhauls at frequent intervals and turns beaucoup RPM but the 300 is never going to pull the kind of revs where needle bearings are going to pay off.
It's not that it won't work, it's just that there are a LOT better places to spend your time and money.
It's not that it won't work, it's just that there are a LOT better places to spend your time and money.
Cast cams have absolutly no hardening at all on the bearing journals. This really is only done with billet roller cams.
Cost per horspower is only very very low per dollar.
Jim
Cost per horspower is only very very low per dollar.
Jim
A
Anonymous
Guest
What about little tiny rollers inside the valve guides?
What about...?
No.
What about...?
No.
mattri":34yjsdby said:
8) only if you are building a road racing, or circle track racing engine. anything else they dont work well. roller bearing cranks tend to twist where the journals are pressed together when you launch hard. the cost is not worth the power gains even at the formula one level.
But your GS 1000 doesn't weigh quite as much as an F150. Seriously, even in a car as light as a VW Bug, they had problems with roller cranks getting twisted if you launch hard. Absolutely no problem with a rolling start as used in nearly all road and oval racing but that initial hitwhen the Xmas tree flashes and you drop the hammer can make a big $$ pretzel. The Suzi just doesn't have enough inertial mass to cause a problem
8) porsche did experiment with a way to prevent the cranks tendency to twist, they cut splines in the journals to prevent twisting, it worked, but it was very expensive, and if the splines had any stress risers in them they tended to break and completely destroy the cranks.
A
Anonymous
Guest
Which is why pretty much everyone with an early GS welds their crank when putting out significantly more power than stock.
-=Whittey=-
-=Whittey=-
A
Anonymous
Guest
What if you could somehow design and build an engine with tapered roller bearings at each end for crank mains with rollers in the middle.
twentyover
Well-known member
Juggernaught
You can do that- using the taper rollers for thrust and the rollers in the center mains. But why? Frictional loses would be reduced, but enough to justify the expense? Certainly not on a log head six.
Remember that if you can think of it, someone else probably has also, and if it's not being done, there' usually a reason (for this, the expense of roller bearings and needing to shim the bearing cine for the taper roller to get correct thrust come to mind.
Don't want to stifle creative thinking, but if you can think of something, you must also think of why it might not work, why aren't people doing it today.
There are lots of reasons roller element cranks aren't widely used on 4 stroke engines, money being the biggest. But you need to determine if the costs of a proposal outweigh the benefits. The aforementioned Suzuki motors probably maintained roller cranks because Suzuki had built up crank making capacity from their 2 stroke operations when they started building four strokes. I can make it myself or pay someone- if I have excess machine capacity, even if my built up crank costs more than a single piece, it may be economic becuase my machine utilization is up.
Lots of reasons. Usually driven by economics, not by the intrinsic value of the design.
When Suzuki got into 4 strokes deeply, they switched to single piece cranks. As volume increased, they could make payback on new equipment.
Simple economics
You can do that- using the taper rollers for thrust and the rollers in the center mains. But why? Frictional loses would be reduced, but enough to justify the expense? Certainly not on a log head six.
Remember that if you can think of it, someone else probably has also, and if it's not being done, there' usually a reason (for this, the expense of roller bearings and needing to shim the bearing cine for the taper roller to get correct thrust come to mind.
Don't want to stifle creative thinking, but if you can think of something, you must also think of why it might not work, why aren't people doing it today.
There are lots of reasons roller element cranks aren't widely used on 4 stroke engines, money being the biggest. But you need to determine if the costs of a proposal outweigh the benefits. The aforementioned Suzuki motors probably maintained roller cranks because Suzuki had built up crank making capacity from their 2 stroke operations when they started building four strokes. I can make it myself or pay someone- if I have excess machine capacity, even if my built up crank costs more than a single piece, it may be economic becuase my machine utilization is up.
Lots of reasons. Usually driven by economics, not by the intrinsic value of the design.
When Suzuki got into 4 strokes deeply, they switched to single piece cranks. As volume increased, they could make payback on new equipment.
Simple economics
simon
Famous Member
keep it simple.
on your average 4-stroke engine, be it a straight six or bent eight, you have a pressurized lubrication system and slipping friction on the journals.
That means that on an engine with good clearances and correct oil pressure, the crank or cam journals don´t touch the bearing surface at all. Basically, the journals are hydraulically supported.
To support varying loads during different revs, the oil pressure rises with higher revs.
Now take a look at the needle bearings:
one big advantage for racers - they may be able to support greater loads at a time and especially reduce wear during cold start and idle.
but, other than that, you have a 100% mixed friction ALL the time, meaning the journals will touch the needles and have permanent contact - and permanent wear, no matter what RPM you´re driving.
Unless you plan to turn you six into a blown methanol-guzzling top-eliminator screamer, you probably won´t ever need roller bearings on your cam or crank journals.
on your average 4-stroke engine, be it a straight six or bent eight, you have a pressurized lubrication system and slipping friction on the journals.
That means that on an engine with good clearances and correct oil pressure, the crank or cam journals don´t touch the bearing surface at all. Basically, the journals are hydraulically supported.
To support varying loads during different revs, the oil pressure rises with higher revs.
Now take a look at the needle bearings:
one big advantage for racers - they may be able to support greater loads at a time and especially reduce wear during cold start and idle.
but, other than that, you have a 100% mixed friction ALL the time, meaning the journals will touch the needles and have permanent contact - and permanent wear, no matter what RPM you´re driving.
Unless you plan to turn you six into a blown methanol-guzzling top-eliminator screamer, you probably won´t ever need roller bearings on your cam or crank journals.
Actually, roller bearings are running on a thin film of oil, too. Rollers have much higher speed limitations than plane bearings but they aren't a perfect solution, especially for rods and cranks. Rollers are incredibly sensitive to impact loads which destroy that thin film. The first time your roller cranked engine experiences detonation will be the last time. Your bearings would be history. That's why the roller cranked VWs ran stock compression ratios while the engines forged counterweighted cranks could push CRs into the 12+ level (back in the days of Sunoco 260)
A
Anonymous
Guest
A side 'benefit' of roller bearings is the extremely low oil pressure. I'd have to check my manual to be sure, but I believe 4psi is the spec at 3000rpm on my rollered Suzuki GS.
-=Whittey=-
-=Whittey=-
The main reason for roller bearing for the cam is because of the unreal spring pressure which would pinch through the oil film and trash a shell type bearing.
One source of needle bearings being used is from an outboard motor crank.
Before and after WWII various attempts were made to run roller cranks. Some had bearing races cut in half to fit on one piece cranks. Aston-Martin had one engine that used huge bearing that would allow the crank throws to pass through the inner racer, had a two piece support web that fit between each journal and bearing inner race. Crankcase was mammoth.
The Tucker original prototype engine used a pressed together roller crank. The engines those day were slow speed and low compression. Don't remember if it made it in to production.
One source of needle bearings being used is from an outboard motor crank.
Before and after WWII various attempts were made to run roller cranks. Some had bearing races cut in half to fit on one piece cranks. Aston-Martin had one engine that used huge bearing that would allow the crank throws to pass through the inner racer, had a two piece support web that fit between each journal and bearing inner race. Crankcase was mammoth.
The Tucker original prototype engine used a pressed together roller crank. The engines those day were slow speed and low compression. Don't remember if it made it in to production.
A
Anonymous
Guest
Why couldn't you run individual rollers like most manual trannys have in thier cluster gears? As long as one of them had a provision for thrust, I think it would work. As for the need, I don't think it is their. With alot of motorcycle engines, esp. 2-cycle, the lubrication can be marginal at times. Add to the maginal lubrication very high average crank speeds, and roller bearings look pretty good. As for our engines, if the oil system is set up correctly, the actual friction can be lower than for roller bearings, and there is more simplicity. The only reason to worry is if the crank is overloaded and the oil film can't stand up to it. I don't think this is a real problem, seeing how much load is placed on some of the cranks i have seen that use friction bearings. As for cams, the spring loads are higher, and the cam bores are never as accuratly machined as the crank bores, they simply don't need to be, unless you put insane spring loads and very high rpm engine use in the picture.
