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WR450FGreg

Camshaft grind

11 posts in this topic

Please humour me here, this Wr450F is my first four stroke in many many years! ........

Instead of paying for and installing new performance intake and exhaust cams, couldn't the stock cams be ground (ie. the fat section, not the pointy end) down and valve clearances restored through shimming to achieve the same or similar result?

Obviously you'd have to do your homework on valve lift and stuff first, but i can't see why it wouldn't work and be a much cheaper alternative to paying $200 to $300 for a pair of new cams.

I could be totally off track here, but had to ask the question anyway.

Cheers,

Greg

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Well, the fat section on the cams does nothing, it's always X amount of distance from the bucket - X being the current gap depending on your shims/valves.

The pointy end does all the work - depending on it's profile - it is what determines the lift and speed of lift of your valves, grinding the fat end does sfa.

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Well, the fat section on the cams does nothing, it's always X amount of distance from the bucket - X being the current gap depending on your shims/valves.

The pointy end does all the work - depending on it's profile - it is what determines the lift and speed of lift of your valves, grinding the fat end does sfa.

I think I see where Greg is coming from. If you cut down the neutral part of the cam, you effectively make the lobe higher. Shimming your buckets up to achieve the proper clearance to the newly cut cam would give you a higher valve lift, but I don't think you could do much to increase duration.

I've never had cams ground, but unless you have a pal with a machine shop, I think the custom setup and cutting would be more expensive than new cams. It's a cool idea though and I've never heard of it before.:thumbsup:

I just checked out your website - also cool. I used to roadrace and a fella at our track had a TZ 250, beautiful bike. Our track is tight and twisty and Ross was a great rider, so he could mop up the 600's and production 750's. I also saw an open class race on a faster track where a bunch of 250's were running NOS, and could stay with superbikes, until they ran out of NOS. Most of them ran out before the last lap, too bad they didn't have bigger bottles.

Frosty

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Ok, I see where he's coming from to get more lift, you'd also have to fatten the lobe for a longer duration, then there's the crunch issue of lifting too far too soon/late, which can already come into play if you raise the buckets depending on how much you take off the neutral part and how you transition to the lobe.

For what a set of cams costs, I can see the setup and grinding costing similar if not more....

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The "fat part" is the base circle of the cam. In every application, there is a limit imposed by components near the cam as to how tall the lobe can be before it starts bumping into things (this is particularly true in the automotive world, where cams often have to slip through a set of closed circular bearings and lobe height is limited by the diameter of those). Thus, at some point, making the base circle smaller is the only effective way to increase the lift, which is, as Frostbite accurately noted, the difference between the distance of the base circle from center, and the distance of the lobe peak from center. This is how many aftermarket cams are made.

The YZF/WRF 450 is not so limited as to lobe height that the lobe cannot be taller, but from a physical/mechanical standpoint, regrinding the stock cams is a legitimate approach. From an economic standpoint, it's apt to be much less practical, as Matt suggests.

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The "fat part" is the base circle of the cam. In every application, there is a limit imposed by components near the cam as to how tall the lobe can be before it starts bumping into things (this is particularly true in the automotive world, where cams often have to slip through a set of closed circular bearings and lobe height is limited by the diameter of those). Thus, at some point, making the base circle smaller is the only effective way to increase the lift, which is, as Frostbite accurately noted, the difference between the distance of the base circle from center, and the distance of the lobe peak from center. This is how many aftermarket cams are made.

The YZF/WRF 450 is not so limited as to lobe height that the lobe cannot be taller, but from a physical/mechanical standpoint, regrinding the stock cams is a legitimate approach. From an economic standpoint, it's apt to be much less practical, as Matt suggests.

Thanks for the info Greyracer. It's nice to hear from someone who actually knows, I just made the assumption on the fly.

I'll make another assumption here, based on Greg's website and list of owned bikes, that he has a machine shop, or has a buddy in the business.

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I'll make another assumption here, based on Greg's website and list of owned bikes, that he has a machine shop, or has a buddy in the business.

That may be, but no machine shop outside of those that specialize in grinding cams have cam grinding equipment. In this day and age of CNC technology, such equipment is actually a little more accessible, but there are still a huge number of issues involved in the shape of a cam lobe. Timing, the point at which the cam opens and closes, and the lobe center split, the distance in crank degrees between peak exhaust lift and peak intake lift, are both more important that either lift or duration to how a cam performs, and in fact, up until the '06 YZ450, the WR used the same cams, timed differently on the exhaust side only. It was very common before the advent of auto decompression to simply move the exhaust cam back a tooth to convert the bike to YZ timing.

There is also the length of the quieting ramps, valve acceleration curves, time at peak lift, etc. This is all separate from the question of retreating the cam surface after the grinding process.

I am not saying he can't do it, but he needs an education beforehand. It isn't as simple as it may look.

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Thanks for the nice comment about the website Frosty.

I've got a little home workshop with a bunch of machinery, but nothing suitable for a crank re-grind.

Besides, I certainly don't have the skill to be able to attempt it myself and no, I don't have any friends in the business, so it's all very much "pie-in-the-sky" thoughts at the moment.

I appreciate all the responses guys, thank you.

It's probably not worth the hassle, I just needed to air my thoughts, see what everyone thought about the idea.

It's sounding less feasible.

Greg

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That may be, but no machine shop outside of those that specialize in grinding cams have cam grinding equipment. In this day and age of CNC technology, such equipment is actually a little more accessible, but there are still a huge number of issues involved in the shape of a cam lobe. Timing, the point at which the cam opens and closes, and the lobe center split, the distance in crank degrees between peak exhaust lift and peak intake lift, are both more important that either lift or duration to how a cam performs, and in fact, up until the '06 YZ450, the WR used the same cams, timed differently on the exhaust side only. It was very common before the advent of auto decompression to simply move the exhaust cam back a tooth to convert the bike to YZ timing.

There is also the length of the quieting ramps, valve acceleration curves, time at peak lift, etc. This is all separate from the question of retreating the cam surface after the grinding process.

I am not saying he can't do it, but he needs an education beforehand. It isn't as simple as it may look.

Trust me, this is well over my head. You've got a carpenter visualizing how to do this on a wood lathe, haha.

If he's thinking of simply increasing the lift, he could machine the base circle only, and wouldn't hve to mess with the lobe at all, except to make sure that he has a smooth transition between the base circle and the lobe.

At first glance I thought that since the base circle would be smaller, you'd have to machine away a bit of the lobe ramp to match, so you'd decrease your duration. I just drew a couple of circles on a piece of paper and realized that you could actually increase lift and duration by grinding the base circle only. It seems like it wouldn't, but it would.....I think.

It would be a fun project but I don't think it would be cost effective over aftermarket cams.

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If he's thinking of simply increasing the lift, he could machine the base circle only, and wouldn't hve to mess with the lobe at all, except to make sure that he has a smooth transition between the base circle and the lobe.

Not true. The timing and duration are affected, and must be taken into account.
At first glance I thought that since the base circle would be smaller, you'd have to machine away a bit of the lobe ramp to match, so you'd decrease your duration. I just drew a couple of circles on a piece of paper and realized that you could actually increase lift and duration by grinding the base circle only. It seems like it wouldn't, but it would.....I think.
See, you figured it out. :thumbsup:
It would be a fun project but I don't think it would be cost effective over aftermarket cams.
You're right about that, too.

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Not true. The timing and duration are affected, and must be taken into account.

See, you figured it out. :thumbsup:

You're right about that, too.

OK, I'm going to quit while I'm ahead. Haha

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