Older XR250 - What Cam?

[Jh85]

It's a 1990 XR 250 with a 280? kit from xrsonly. I needed a few odds and ends to get back into shape, the cam is the final step. I probably dont have to replace it but while it's apart I figured I would dig in deep.
There seems to be several different cams from several different shops. I was just wondering if anyone has been through this before and had some good advice.
BTW Out east here I was hesitant to get a full race cam but figured it would go well with the oversize piston. Suggestions?
Thanks in advance

 

[parish8]

where do you ride? what other mods do you have? it is my understanding that the cam is kind of far down on the list of things to do. exhaust, carb, big bore kit all come first then mabey some head work including porting, vlaves and a cam. i don't know alot about xr cams, the only one i have seen is an "all around cam" i think they called it.

 

[Jh85]

Southeast MA. Ever hear of New Bedford? Well I live in Acushnet, about 5 minutes from New Bedford. I like to call it the "Arm Pit of Cape Cod"
Long story short.
I bought the bike broken for a very reasonable price. It was origanily the kids father's friends bike. All the work on it was done by or with parts from XR's Only. His father got the bike for a good price from his friend. His parents got divorced he moved to Acushnet. It broke over the summer, he never fixed it. Got sick of looking at it. Sold it to me for another very very reasonable price. I fixed the problem, broken counter-shaft. Now I'm finnally getting it back together.

The List:
Supertrap Exhaust.....check
2mm(I think) overbore ......check
valves.........good shape not sure if they are stock or not
head work + porting ???
Carb?? I don't even know what the stock XR 250 carb is?
the shock looks like it has been recently serviced(plastered with XR's Only stickers with new spring)

I thought about eventually getting a pumper carb or pulse charged- I don't know i've heard good things about both. Maybe even a CR fork conversion depending how thick my wallet is. If not that I might make my own fork brace or instead of killing myself I'll bite the bullet and buy the Scott Summers one.

Back to the Cam. While taking it apart I noticed a small score or mark on the top of one of the lobes. I figured it was a good excuse to get a new cam, I just don't know which one.

Heh. Sorry for the long post.

 

[SFO]

If the cam was/is scored ...

check the rockers and make sure they are good.
Chances are if the cam is toast so are the rockers.
I would run kmpi valve springs and a megacycle torque cam for your conditions. I think there might be updated rockers as well.
Hey Ochster! Where are you for this individual? This is your bike!

 

[Jh85]

Everything else seems fine. Only one of the lobes is scored/marked. If someone can post some pictures for me I can mail them to you Tuesday.

Thanks,
Jared

 

[SFO]

Chain of events

The more I think about it, I want to plug oem.
Building up a rfvc head with the right cam,rockers, springs, valve guides, and valves is not an experience to do half heartedly.
If you want a no brainer runner oem is unsurpassed.
Also check/replace the wave washers that suck up the axial free play on the rockers. These fail as well.
I hate to bring you down but I want you to know all the implications of trying to get one of these heads to work.
Ochster?

 

[Jh85]

Well the main problem is that I don't know what I have in there. If I run an OEM cam there is no way it would do any harm to a modified head, Right?
If I do get some pics could you/anyone else tell what I do have in their?
Thanks,
Jared

 

[parish8]

it seems like honda makes a slightly bigger cam, it shouldn't need the after market rockers. Ochster?

 

[ochster]

jh85, I would agree with SFO's comments on the RFVC head!

It has been my experience that there is definately more performance to be had, but it involves upgrading more than the cam. The rocker arm pads that ride against lobes typically will wear, and ruin the cam in the process. The answer I have found, is to have the rocker arms "hard welded". This adds a thicker and harder face to the rocker pad, than what exist oem. The company I have been using with great luck, is "Megacycle". A good quality spring kit, like something from "kibblewhite performance" would also be a neccesity. I would also at this point consider upgrading to a stainless valve, and having a quality valve job peformed. The oem valves do not seem to hold up well in this environment, with increased spring pressures, and harder use. You should also be prepared to replace the guides, and possibly valve seats, judging from the year of your bike and previous usage. Once doing this, the head and valve train become a very solid performer!

I personally am not one who thinks there is enough "torque" in these smaller displacements, to design a engine around. Atleast not for the intermediate and up level rider. The 250 is a very willing and able revver, I like to use a cam that enhances the mid to top. You will achieve a torque gain, simply by going up in displacement. If your simply playing around and wan't user friendly power, I believe the oem cam to be a decent choice, especially with a 77mm or 78mm piston kit. For faster use, the two cams I have been using are "Megacycle" products. The #154-x5 is a very good all around profile, with a good top end. Mated with a 10.5:1 JE 78mm piston I think this is a nice build up. Thier #154-20 is full on race- "Rev". For guy's who are trying to compete in some of the more open style racing, revs are good. At this level/style of riding and engine tune, you need to expect a fair amount of maintenance issues. This cam requires a high compression piston, upwards of 11:1, wich will neccesitate the use of a quality fuel (race gas). I have a bike set-up with this cam and a 36mm pumper, that I like very much, but it completely changes the attitude of this engine.

There is another link here that needs to be checked, if your truly wanting to go all the way with this engine. That is the crank rod! If your going to spin these things up with high compression piston, the oem rod will eventually be the weak link. It is nice to eliminate that with a Carrillo or other product. My last build-up was done with a Carrillo, and balanced by Falicon.

There is a member here "DualSportr", that I'm sure could provide you some info based on dyno charts. I do not have that. I'm also sure she could elaborate further on my cam choices...

I was helped by SFO (he's an insider), on my last head build-up. It is a work of art, I'm sure he can give you a referal if you were interested. All machine shops, are NOT created equal.

I simply enjoy working on, and riding these air cooled "dinosoars". And at the end of the day when riding with a group of newer bikes, the rider is still the difference! I love it. Have fun!

 

[Jh85]

That's what I was looking for. Thanks.

I think I've decided that I'm going to go with the stock cam. After proding and poking inside the engine I found out that it has a few modifications already.(I wasn't sure before) Some kind of aftermarket valve kit is in their. It has a 78mm, 11:1 JE piston. A messed up reground cam, done by XRs Only. The valves themselves have two markings. Two have K6 on them, the other two have K1 marked on them. The cam itself had some numbers on it, I forgot what though, I'll have to check on Thursday when I go back to work. I'll have some pics up soon.

Since I already have your attention a few quick questions.
What kind of exhaust are you running?
Have you ever thought of doing a fork conversion? What about a steering dampener? Fork brace?
What made you decide on the Pumper over that pulse charged intake system?(I think that's what it's called)
Thanks Once More,
Jared

 

[Jh85]

Here is a valve spring with some kind of spacer underneath:

The rocker arms:

I hope I did that right :confused:

 

[ochster]

jh85,
Those springs look like a "R&D" kit with aluminum retainers. The "spacers", are normal for that kit.

Hard to tell in the photo, You can tell by being able to fell the edge to the plating, and or gouges and scratches. It also appears there is some bluing? I find it the rarity, when someone has had the rockers hardcoated, when installing a new cam. Unfortunately the old rockers quickly wear, taking out the new "cams" lobes with it. XR's Only may have provided the parts, but they do not grind cam's. This is most likely a customer decision based on $$, and is the reason "SFO" was promoting the oem set-up. To do it right includes more than simply installing a cam and springs. If infact they are worn, they will continue to go downhill quickly, The only solution is to fix/replace the componets.

I use a oversize header with a XR's Only megaphone with a trapp, this is on a fully modded motor. I also have a mildly modded 78mm piston motor, that utilizes the oem header and White Bros E-series muffler, and oem carb. It is a great woods set-up.

I have utilized both convential and upside down forks on several conversions. It can be alot of work, but for fast agressive riding is a big plus.

I have never used the "pulse charged intake" set-up. But I do not equate it on the same level of performance as the pumper.

 

[SFO]

If you had seen what I've seen...

You would bin that spring kit pronto.
You probably have a megacycle cam too.
Barbara at megacycle sells R&D spring kits with her cams.
I would do a 100% inspection of the head and report back.
I bet it has shortened guides too. I'd like to know how they feel.
First thing though is to send your rockers into megacycle to get welded up.
While your waiting we can tackle the rest of the head...:eek:

 

[Jh85]

Ahhhhh

First Ride Today - Woooooooooooooooooooo Hooooooooooooo

That is one fast little bike. It seemed like I would never get to ride it. It was only a 20 mile ride, but it was still good enough to get to know the bike.

Next - Fork brace and SS

More later.

 

[SFO]

I love these bikes...

I won my first (and last) race on one of these bikes!!!
What combination did you settle upon?

 

[Jh85]

I ended up getting the cam from XR's only, it was the 02-1030 Competition Cam. I left the rockers, springs and retainers in there.

I hope to race next month with it. The only thing that I think needs some attention is the front end. It seems to "drag" into others lines on rutted trails. Almost a vague feeling. If I remember right this is caused by fork flex, right? SRC wants $200 for their brace and there is another company I heard someone talking about that has one for $100.

To me that seems like alot for a chunk of aluminum. If someone would give me the dimensions I think I might try to make one myself, I dunno yet.

Happy Trails,
Jared