Engine questions

[USMC1STSGT]

I am somewhat of a newbie, (Although I grew up on an '86 atc250r)

I think I have read every post from the last 2 years trying to learn everything I can about these awesome bikes. But I have come up with a couple of engine questions, hopefully the experts can steer me in the right direction.

It is a 310 pro-x and I was told it was ported by CT, but it isn't engraved, so I cant be sure. It will only be ridden on dunes. I like to do hill climbs and some racing. I will get a new pipe (PT eliminator, ESR-5) and a PWK39.....I am trying to do everything mid/top end.

I know there are some differences between the model years on the engines. How can I tell what year my engine is?

I have no idea what type of porting I have, so do you recommend that I just pull the cylinder and send it to someone to have it checked?

If it is ported incorrectly, can that be fixed/adjusted or do I need a new cylinder?

I could just take the whole engine to Duncan or CT, because I also want to know if I have the other usual mods, like CR ignition.

All advice is appreciated.

-Gary

[All250R]

Originally posted by USMC1STSGT
I am somewhat of a newbie, (Although I grew up on an '86 atc250r)

I think I have read every post from the last 2 years trying to learn everything I can about these awesome bikes. But I have come up with a couple of engine questions, hopefully the experts can steer me in the right direction.

It is a 310 pro-x and I was told it was ported by CT, but it isn't engraved, so I cant be sure. It will only be ridden on dunes. I like to do hill climbs and some racing. I will get a new pipe (PT eliminator, ESR-5) and a PWK39.....I am trying to do everything mid/top end.

I know there are some differences between the model years on the engines. How can I tell what year my engine is?

I have no idea what type of porting I have, so do you recommend that I just pull the cylinder and send it to someone to have it checked?

If it is ported incorrectly, can that be fixed/adjusted or do I need a new cylinder?

I could just take the whole engine to Duncan or CT, because I also want to know if I have the other usual mods, like CR ignition.

All advice is appreciated.

-Gary

Hi Gary,
I'll try to help by starting with a general statement about buying used 250R's/bikes. If you want it to last and not give you any surprises, and you aren't pretty sure about the maintenance in the engine and chassis, people should pull these items down and go through them with a fine tooth comb.

That said yours looks really clean! So, maybe the owner kept up with maintenance and the cost of doing anything more will be small. A lot of maintenance items go unchecked though when it comes to harder to get to items or items that require more knowledge and tools. One of those items is the bottom end. You need a variety of specialty and machinist tools to do a 100% check on things. Bearings that have been in there a long time go bad and often take other items like gears with them. It's not something to be scared of, but it's something to not be surprised of if it happens.

Having said all that, I started my business initially out of necessity for my own bikes after I got some horrible, incomplete work done from ESR (to be specific). I had enough experience and aptitude to gather the tools and books and invest in myself and then a small business. You can send your engine in to CT or Duncan and maybe get great results, but if you've read a lot you know probably that results vary. It's tough to find someone to give you custom, quality reliable results every time. Employees I think are hard to trust when they don't work for you. Sometimes you have to just do it yourself to be sure. There are quality smaller builders out there you can easily find. The choice there is yours.

At a minimum you should invest in a service manual and a quality compression gauge to keep an eye on the top end with. Go through the intake tract and check that the rubber is sealing and doesn't have sand or dirt inside. That will give you an idea on your own how intact the top end might be. The bottom end isn't quite as straight forward and so there are lots of people inclined to increase hp by 10-15 but didn't see how healthy the bottom end was. It's not glamorous and doesn't add to power, but I've become a believer in taking care of this part as a prerequisite for buying and building an engine.

There are several lube points in the chassis you want to pull off and get some grease into. I always find the brake pedal and rear shock upper collar are bone dry. The swingarm pivot bolt and linkage in particular need inspecting and service. The chassis isn't too difficult to navigate and service. Honda did a really good job making it easy to work on with a small amount of tools.

What year your engine is isn't as important as what's inside it now. The main difference the average guy needs to know is if it's a short or long rod crank. You have a Pro-X though so that narrows your choices down. For reference the 86 came with a 125.3mm crank, the same as all or at least most year CR250 engines. In 87 forward 5mm's were added. I can't tell if you have a spacer plate under your big bore but your engine looks like an 88-89 from the paint color so unless it's been customized it's probably a standard long rod with the CR style piston which is very typical. It could be stroked, and to measure that the engine needs to come apart.

The CR ignition doesn't have provision for lights unless it's been customized further, and has a really small flywheel. If you open the cover and you see a custom backing plate and a little flywheel you have the CR ignition most likely. Otherwise it's probably stock.

Porting in my opinion is done "incorrectly" mostly if it doesn't fit what the customer wants or is poorly matched with the pipe the customer wanted to run. The rest is fine tuning and customization, and more than porting goes into that category. So I'd say that unless you don't like how it runs, it's probably good enough for now at least. One of the first things you should appreciate about your R is that it doesn't cost a lot to keep running and running well once it's in healthy shape. You don't have to worry about valve train or engine oil and you always know you can beef it up to 70-80hp whenever you want to. I think it's good to get to know what you have so you're better equipped to voice clearly what you want to change when you're sure, and you're doing it on your own terms, not because it's broken or already apart. So if you can get way with it, do your maintenance and then don't fix it if its not broken, and enjoy that for a while. Hope to see you in the Glamis dunes! :D

[USMC1STSGT]

Thanks for all of that good info! It does not have a spacer plate, what does that mean, that it is the shorter crank?

I already got the honda manual, so that will help with the service.

Here is a copy of the dyno run with the current components.

-Gary

[All250R]

If there's no spacer plate, it sounds like you might have a short rod crank. Short rods yield a slightly more aggressive port time/area but less dwell at TDC and BDC.

Regarding your dyno, and any individual component like rod length, there is almost no end to the combinations that can be put together to change the power curve. That little dip in there looks like a soft spot caused by something not quite in tune, but your peak number isn't aweful. There's room for improvement for sure especially if you want a mid/top engine for Glamis. If you want the overal system to be inspected and modified for performance, your best bet is to commit to all of it at once. The dune season is coming really soon though. Otherwise, I don't think you're doing too bad for now. A bigger carb or a different, possibly more aggressive pipe like an ESR 5 or 11 might add a few easy ponies to your setup and can be custom built to later.

[USMC1STSGT]

I go to the Oregon Dunes every Thanksgiving, so I want to have this bike perfect for that trip.

What I would like to do is tear the engine down and inspect/repair everything. Then start fresh with a new clutch, carb and pipe. Who do you recommend I have do the work?

[Master LTR450]

Talk to Neil (C-Leigh Racing) he knows what he doing from what everyone else says, seems to have a top notch rep!!! I have also heard nothing but good about Arlen (LRD)

[All250R]

Check PM.

[havinnoj]

Hey bro welcome to R's. Do you have a dyno over RPM? THose numbers look okay for CT. What is your rider weight?

Concerning people to perform motor work for dunes only, I'd stick with the shops that specialize in that. Living 10 minutes from LRD, seeing the motors they produce, and having had them build me a motor myself-- your money is better spent elsewhere.

I hear nothing but good things from Neil as well, however I've never seen any of his motors run out here in Oregon.

Truely top notch builders for sand bikes are Packard ent, Pete at Piranah ent (Oregon), MAC Racing, and my builder Dave Moore Racing (OR). There are lots of good builders but these guys really specialize in R's and inturn have the times and trophies to back it up.

PM me if you want to chat further.