Why don’t more motorcycles use hydraulic valve lifters?
We got this comment / question at the end of an article on Harley davidsonis new Max Revolution Steve Sweetz’s engine, and it’s an excellent:
Here’s my question in that vein – why aren’t hydraulic valve lifters more common in bikes? Why did it take Harley-Davidson, of all companies, to shame the Japanese and European manufacturers in this regard?
I understand they don’t perform well at very high revs, but motorcycle engine designs increasingly tend to have bigger bores, fewer cylinders, lower revs in the name of fuel efficiency and reliability, anyway.
It seems harder and harder to find a mechanic who can replace a tire without screwing up something (seriously, the last time I had a tire replaced the bike was handed to me with an unbolted brake caliper) . Of course, I don’t trust any of them anymore to properly perform a valve clearance check on very compact modern bikes that are very difficult to work on in general – and unfortunately I don’t trust myself to. neither do that.
The era of motorcycle valve clearance controls must end! Hydraulic valve lifters have been standard on cars since the 1980s.
You said it, and we can only agree, except to add that they have been standard on cars since well before the 1980s. The only reason we don’t complain more about the settings of the valves is that we always return our borrowed motorcycles to their maker before we get there. And in this regard, some motorcycle manufacturers are better than others. my 2000 Yamaha R1 still hasn’t driven 26,600 miles for his first valve inspection, but I’ve never driven him. We know at least a few Ducati fans who buy a new bike every two years, selling the old one just before its expensive desmo valve service is due. Caveat emptor Indeed.
Perhaps a little explanation is in order first for our readers who grew up in the non-mechanical age. There should be some free play between the parts that open the intake and exhaust valves – the lifter or lifter – and the valve stem itself, to account for thermal expansion and pressure. wear. This clearance decreases over time, because the valves very gradually wear out their seats, and must be restored. Simpler motors use screw and locknut adjusters. Most modern engines use chocks. Usually, a thinner shim is needed to regain the factory clearance.
Valve clearance inspections are required between 6,000 and 26,600 miles (for many Yamaha). On bikes that require valve inspection, someone will have to go with their feeler gauges to check and reset that clearance between the valve and lifter to factory specs. It is a tedious task that takes time, some bikes more than others, and even requires mathematics if shims are involved. Wedges are small round spacers of different thicknesses.
Hydraulic valve lifters
And in this corner, hydraulic valve lifters. These have been around for many years in automobiles, in Harleys from the 1948 Panhead onwards, and also in the Indian ThunderStroke engine which serves as the main image. Basically what happens is that pressurized oil is injected into each valve lifter and sealed inside as the lifter moves into its bore, thus maintaining valve clearance, or gap, constantly at zero as the engine wears out. The conventional wisdom is that hydraulic lifters cannot move as quickly as mechanical or solid lifters, but many people have been willing to make this small sacrifice for the greatly reduced maintenance requirements.
For engines running at less than about 5000 rpm, like most engines in large cars, hydraulic valve lifters were perfectly adequate. In ancient times, HOT ROD magazine and others were filled with advertisements for solid tappet camshafts, to open and close valves faster and higher for increased power. Solid lifters meant you had to make valve adjustments every now and then to maintain the right clearances, but it was kind of fun when all you had to do was remove the huge valve covers from your V-8, lean on the fenders and pull the zippers out of the canned drinks while you twist the big nuts at the top of the rocker arms of your old pushrod motor. Thinking that the job would be just as easy on my new 1986 Honda VF500F Interceptor was a valuable learning experience.
Solid lifters are better
Like so many things, it all depends on who you ask. We asked Honda and got this from our media rep Colin Miller:
We have not had HVA (hydraulic valve settings) in our units since the VT1100. It was the last one I can remember. Some thoughts from my time on the service side and other people I have spoken to:
HVAs are a good idea for some applications, but they have drawbacks. They require the system to be much more complex due to the need to add actuators in the valve system as well as a more complex oil supply system. At higher engine speeds, HVA systems tend to swell and can cause the valves to float.
This can be a huge limitation for motorcycles as they often have higher engine speeds than automobiles. HVA systems require that the oil supply be kept very clean to prevent build-up or debris from causing problems with the actuators. Bucket and wedge or screw adjusters take up less space, weigh less, and are less expensive in design and manufacture.
When it comes to automobiles, many Honda cars do not have HVA either. Even my 2004 Toyota Tacoma has chocks that need to be checked.
Hmmm, we also remember the long Nightjar 750 having hydraulic valves. The coolest were the first, the Nighthawk 700S produced from 1984 to ’86. It had hydraulic valve lifters as well as a redline at 10,500 rpm – a shaft drive as well. Honda continued to launch them throughout the 2003 model year.
Hydraulics is the way to go
Here is the official word from Harley davidson on the subject, whose new Revolution Max engine is rated at 150 horsepower at 9,000 rpm.
Harley-Davidson has been using hydraulic valve lifters since the introduction of the 1948 Panhead, so we clearly have a lot of experience with this technology. For OHV (overhead valve) engines, like the Milwaukee-Eight V-Twin and other OHVs, it is very common to use hydraulic valve lifters for the obvious advantages. Where it gets more difficult is with OHC (overhead cam) engines. Here again, Harley’s in-depth knowledge in this area helped meet the engineering challenge.
For the development of the all-new Revolution Max powertrain, Harley-Davidson engineers chose to incorporate hydraulic slack adjusters (HLAs) on each cam to eliminate maintenance, reduce noise and accommodate more aggressive cam profiles with reduced ramp lengths. Harley-Davidson used advanced valve simulation techniques when designing the cam and carefully considered peak loads and valve lift to ensure the HLAs work with the cam. The cam profiles were also designed taking into account the use of a high speed HLA. Oil aeration, which is an enemy of HLAs, has been minimized throughout the powertrain. The result is a high performance OHC motor with the benefit of hydraulic valve lifters.
The only big V-Twin in our recent Heavyweight Nakeds shootout, the KTM 1290 Super Duke R, peaked at 9,700 rpm with 159 horsepower at the rear wheels. Its eight valves will need to be checked every 18,600 miles. Meanwhile, the Harley Pan AmericaThe new Revolution Max V-twin delivers 134.5 hp at 9200 rpm at the rear wheel of Mickey Cohen’s dyno, but its hydraulic valves should never need to be adjusted.
In all fairness, many recent models of bikes without hydraulics seem to retain their valve clearance very well: a quick glance at a few forums reveals that most KTM 1290 valves were to specification at the time of check, and this also seems to be true the BMW K1600 24-valve in-line six in its 18,000 and 36,000 mile checks. Yet just checking these sets can take a lot of disassembly and therefore expense, even if no tuning is required.
Ultimately, it’s in the buyer’s hands: what is more important, ultimate performance or great performance with low maintenance?
On a personal note, I got a little wet the other day when someone online wrote that my new Jaguar, 20-year-old 32-valve V-8 would need a valve tuning on its anniversary of 100,000 miles. Taking deep breaths and checking the plant’s maintenance schedule revealed no such requirements. This is because, according to another online expert who is, “These engines are designed so that the valve seat wear is roughly equal to the valve lift wear, so the clearances remain unchanged.” If the car has delayed oil changes or other issues, that balance may be upset and require repair, but that would be unusual. This is an area where Jag design has always been good.
How smart is that?
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