A look inside the CRF150R

Rich Rohrich · Feb 5, 2007

I'm in the process of tearing apart a CRF150R to document and blueprint the engine. I figured I would share a few pics of some of the internal parts in this thread for those who haven't seen what's under the covers.

As you'll see in the pictures I post over the next few weeks, this is a really slick design and there is no doubt this is a REAL race engine.

Take a close look at the piston side view and you'll see skirt is so short that it doesn't even extend as far as the pin boss. Single compression ring, with a standard 2 rail oil scraper package. This is a serious F1 inspired piston that won't last long when run hard.

Rich Rohrich · Feb 5, 2007

The cam gear uses a removable cartridge setup to support the cam. It's very similar to the CRF450 design, and is welcomed by most of us who found the CRF250 design to be a bit of a PITA by comparison.

It differs from the CRF250 and 450 by using two separate exhaust roller rockers each with it's own cam lobe, rather than the single lobe single rocker setup of the bigger bikes.

oldguy · Feb 5, 2007

This is really going to be interesting I hope we get to see everyting and the explanations will be invaluable to any future owner. Rich tearing into a brand new engine kind of makes me think back to the old 'Incredible Journey' book where the scientists get shrunk down and go into the human body

IndyMX · Feb 5, 2007

That's one hell of a macro setup you have there Rich.. I can't wait to see the rest of the series on this!!

gwcrim · Feb 6, 2007

I've never seen such a short piston. Would the aftermarket be able to extend skirts for longevity?

Rich Rohrich · Feb 6, 2007

gwcrim said:
I've never seen such a short piston. Would the aftermarket be able to extend skirts for longevity?

Sure they could, but they would also have to make it heavier which would require lowering the rev limiter to keep the loading the same on the parts. Unfortunately physics doesn't care how often we have to change pistons. :)

I for one am glad they built a real race engine. People who want a reliable trailbike engine have tons of good options.

Rich Rohrich · Feb 6, 2007

IndyYZ85 said:
That's one hell of a macro setup you have there Rich.. I can't wait to see the rest of the series on this!!

It's a fairly inexpensive ($399 new) 60mm F2.8 Nikon 1:1 macro lens in the top 3 pics, and a cheapo 18-35mm F3.5 Nikon lens I picked up used in the bottom pics. Controlling the lighting makes all the difference in the end.

IndyMX · Feb 6, 2007

As I am finding.. I just got a new Tamron f/2.8 17-50mm. This lens is so much better than that POS that came with the 20D.

I plan on getting a macro lens soon, but I'm not sure which I want. I can get a 60mm f/2.8 or a 100mm f/2.8. Just not sure if the $100 extra for the 100mm is going to be
worth it.

Rich Rohrich · Feb 6, 2007

IndyYZ85 said:
I plan on getting a macro lens soon, but I'm not sure which I want. I can get a 60mm f/2.8 or a 100mm f/2.8. Just not sure if the $100 extra for the 100mm is going to be
worth it.

Working distance from your subject will really determine the focal length you need. For small parts shots I use the 60mm Nikon macro, for things outside like flowers and small animals where I want to put a bit more distance between myself and the subject I use a Sigma 105 F2.8 macro lens These shots are an example http://dirtrider.net/forums3/showthread.php?t=145792.

I think a 200mm macro would be a better choice by the cost of the good lenses has kept me away.

oldguy · Feb 6, 2007

letsride24-7 said:
How many hours are on that motor?? I think that piston looks cheap, it looks like pin boss is oblong and chewed up. But other than that, this is going to be a sweet thread. I can't wait till you really get into it..

I don't think Rich has ever started this engine. He is funny that way gets his kicks tearing into a brand new engine putting it back together then thrashing it

Rich Rohrich · Feb 6, 2007

It's brand new. ;)

Ol'89r · Feb 8, 2007

Very cool Rich. :cool: Can't wait to see the rest of it.

Are the valve shims the same as the 250's?

What diameter are the valve stems?

Awesome photos. :cool:

YZ165 · Feb 9, 2007

This is gonna be cool....Nice Rich!

ChopperDave · Feb 10, 2007

Great pics Rich! That 150R looks like it is going to be a serious bike.

Rich Rohrich · Feb 10, 2007

Ol'89r said:
Very cool Rich. :cool: Can't wait to see the rest of it.

Are the valve shims the same as the 250's?

What diameter are the valve stems?

Yep, 250 shims. 1.90mm intake 2.20mm exhaust are the stock sizes on this one.

Intake valves are two piece all steel (cheap stuff not stainless) 26mm with 4.5mm stems.

Exhaust valves are two piece, steel stem fused to what looks like an Inconel head like the 250 uses. Same 4.5mm stem.

Port to seat transitions aren't perfect but not bad for an inexpensive production head.

No back cuts on the valve from the factory, or radius on the edge of the exhaust valve.

Rich Rohrich · Feb 10, 2007

Here's a couple of pics of the valve seat insert to port transition on the intake side. The pics aren't great but hopefully they show that while the transition is far from perfect, from an airflow point of view it's pretty damn good for a $200 production head. The inclusions you see won't make much difference to the mass flow of the port.

I'll get some better pics once I figure out the correct way to light the port. In the mean time, here's a different view of an intake port than you might be used to seeing.

Rich Rohrich · Feb 11, 2007

Here's a couple of 100% crop pics of the insert to port transition. I kinda blew the DOF center point so they are a bit blurry in parts. :bang:

IndyMX · Feb 11, 2007

That's just amazing.... Can't wait to see it with good lighting.

Ol'89r · Feb 11, 2007

Rich Rohrich said:
In the mean time, here's a different view of an intake port than you might be used to seeing.

That's a great shot Rich. Lookin' from the inside-out. ;)

How did you make yourself small enough to climb in the port? :whoa: :laugh:

Looks like there is room for improvement in those engines. Glad they didn't change the shim and stem size.

Keep em coming. :cool:

Chili · Feb 11, 2007

That macro stuff is awesome Rich :cool: Never been inside a 4 stroke but I'd imagine to the naked eye that stuff looks smooth and perfect?

oldguy · Feb 11, 2007

Ol'89r said:
That's a great shot Rich. Lookin' from the inside-out. ;)

How did you make yourself small enough to climb in the port? :whoa: :laugh:

From page one my prediction :nod:

oldguy said:
Rich tearing into a brand new engine kind of makes me think back to the old 'Incredible Journey' book where the scientists get shrunk down and go into the human body

Rich Rohrich · Feb 11, 2007

It's kinda funny, I've read reports on a number of websites from people that were convinced Honda put stainless steel intake valves in this engine. I figured there was no way Honda would go to that expense, and I was right. Plain old cheap steel intakes with a single 45 degree face cut and no back cut angle. Here's what it looks like:

Rich Rohrich · Feb 11, 2007

Just for reference here's what a real one piece Stainless Steel Kibblewhite valve looks like.

This is just a test valve I use on the flow bench so the valve face is still rough. It would get finish ground before use in an engine.

Notice the machine marks all the way up the backside of the valve and on up to the stem. These valves are works of art. :cool:

rickyd · Feb 11, 2007

Any Ti in the future? Or is it not even needed?

76GMC1500 · Feb 12, 2007

Those valves could be stainless and just show some mill scale? I don't know that the mill scale on stainles steel would be that black like because most forged stainless stuffs are electropolished afterwards. I've never seen it as forged.

A look inside the CRF150R

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