stroker crank

[kiesta00]

I have an 86 engine and I just ordered a '86 69.5mm piston and I want to order a stroker crank, but the cranks are only available in the long rod 87 model. What size and spacer plate do I need to compensate for the 5mm longer rod? where can I get it? I know the head needs to be cut for the 4mm stroker crank and the port timing altered so I've got that covered...I just need to know about the longrod/spacer plate info...thanks

Keith

[C-LEIGH RACING]

You will need something like a 7mm plate & then cut it down to get the proper piston to deck height, or you could just get a 5mm plate, recut the squish & dome & let the piston run up into the head.
If everythings new, like the cylinder not ported its not so bad setting it all up, but a ported cylinder, it will take 10 times as long to finish it.
Neil

[wilkin250r]

Listen to the man above me. I know a thing or two, but he knows it all. I don't think there is anything I can add that he hasn't already covered. In fact, if you're looking to send your cylinder to somebody to have it ported for your new stroker crank, I'd reccomend him.

One of the main obstacles is that the stroker crank changes all the port timing. On a 4-stroke, a stroker doesn't change the camshaft specs, so your timing is all the same. But on a 2-stroke, the timing is set by the rod length, angles, and so forth, and a stroker crank changes all those aspects. Many people are often upset to hear they can't use their existing ported cylinder with a stroker crank, because they don't understand that their old porting specs were based on the STOCK stroke, and won't work properly with the new increased stroke.

[kiesta00]

so the ESR .190 (4.8mm) spacer plate would work? Would we have enough room in the head to cut for the additional clearance from the increased rod length and stroke?

[C-LEIGH RACING]

The 0.250 plate is what ESR uses for the strokers. That plate might not be listed on the ESR site or in a new flyer sales sheets.
If your going to use the 5mm plate & cut up into the head for the piston, you would be better off getting a cool head with the changable dome & have them pre cut the dome.
Stock heads kinda thin, but it could be machined for the stroke, I just hate to use those angle plug heads.

Neil

[86 Quad R]

as you've come to realize, there are different ways to set up an engine with the 4mm stroker crank. the reason that the 4mill is only avail. in the long rod is due to the extreme rod angle that is created by the added 4mm stroke and the short rod.

as i mentioned in my reply to your pm, you can go with the 87-89 piston(which i'm told is now avail in the bigger bore application by my builder) and not have to run a spacer plate at all. on a stock head, a small amount of the head will need to be milled to adjust the squish band and the chamber(if wanting to keep the compression around 180-190 psi) will need to be reshaped to up the cc's but if you use the cool head, then you can go with larger dome to get the compression where you want it. various thicknesses of head gaskets can also be used to determine squish bands to be cut and so on.

another thing with going this route is that the skirt on the piston will need to be milled about 50 thou, give or take a few. i like this setup because it doesnt require a spacer plate therefor doesnt increase crankcase volume.

as mentioned, regardless of which way you go. you have to have the cylinder ported for this setup and trying to use an already ported cylinder makes it tuff if not impossible.

good luck with which ever route you go. :)

[Rich250RRacer]

I like the set-up I have in my XC 250R. It's a long rod, 2mm stroker, done by Bud Fischer at Fischer cycle. It uses an '86 piston, Pro-design spacer plate and a Cool-head with a 20cc dome. Using a stock thickness, full ATC head gasket I have about 195 PSI compression. Of course the cylinder is ported to match and I run a stock pipe. It makes for an awesome cross-country set up. Bud's work is flawless, he's like a mad scientist, but that's to be expected, he's FORGOTTEN more about building motors and chassis than anybody on here knows.

[kiesta00]

I think I'm going to go with the .250 spacer plate, 86 piston, and 4mm crank...thanks for ALL of your input, couldn't do it alone haha. With christmas approaching, I won't be able to do this until after finals are over this week and christmas shopping is done :ermm:

[Aceman]

Originally posted by Rich250RRacer
Bud's work is flawless, he's like a mad scientist, but that's to be expected, he's FORGOTTEN more about building motors and chassis than anybody on here knows.

That's a bold statement Rich. I wasn't aware you knew how much experience everyone on here has.:rolleyes:

[robyone]

I'm thinking of building a stroker motor also, so all I need is +4mm rod, .250 spacer, 86 piston and the port timimng adjusted?

[Rich250RRacer]

Originally posted by Aceman
That's a bold statement Rich. I wasn't aware you knew how much experience everyone on here had.:rolleyes:

Not to take anything away from anybody on here, but Bud is very good at his work. His knowledge will just floor you if you have the chance to talk to him. It comes from years of experience, he was a Honda dealer for quite a long time, and knows the ins and outs of what makes them work. It could be a killer race motor, or one of his hand-built custom chassis (which truely are a work of art, you really have to see one to appreciate it), it's hard to find better work. If you ever have the opportunity to talk to someone else who's had work done by him, I'm sure you'll hear the same. Laz Sommers is the only one I've seen who's on the same level as Bud. Yeah, I know it's a bold statement, but I stand behind it.

[kiesta00]

Originally posted by robyone
I'm thinking of building a stroker motor also, so all I need is +4mm rod, .250 spacer, 86 piston and the port timimng adjusted?

If I were you i'd go with the 87 piston that way you don't have to mess with the spacer plate and just mill the piston skirt for clearance. The only reason i'm using the 86 piston is because I ordered the piston before I tore the engine down.

How does the power of a stroked engine compare with that of a stock 72mm stroke feel? just curious what kind of animal i'm going to have on my hands :devil:

[jas250r]

I hope you guys keep this topic goig, so can get a better understanding on the stroker setups. So the rod is shorter and the way it gets the longer stroke is the cranke pin position is moved 4mil. So by doing this you get more displacement? By how much? What does it affect the reving of the motor? Does it make for smoother power and a wide power band? What type of riding is this good? To me it sounds like an xc setup but ist a shot in the dark. Keeping explaining please!

[kiesta00]

No...actually on the 85-86 engines the rod is 5mm shorter than the 87-89. The 85-86 piston's pin heigh is also 5mm lower than the 87 piston because of the longer rod on the 87. So when converting an 85-86 to a stroker crank (which comes with the longer rod) the crankpin is moved 2mm (4mm total added movement up and down) so depending on which piston you choose, that'll dictate if you need a spacer plate or not. correct me if i'm wrong lol

[C-LEIGH RACING]

That is right kiesta.

Now lets throw a knott in the water hose, use a 5mm stroker crank :eek2: :p :p .
Neil

[kiesta00]

wilkins you have a pm

[robyone]

So I have a 86 crank that I want to make a 5mm stroker....what all do I need?

[C-LEIGH RACING]

Originally posted by robyone
So I have a 86 crank that I want to make a 5mm stroker....what all do I need?

You can send that 86 crank to ESR & they can stroke it for you to a 5mm.
What will be done is the two halfs will be machined for the + stroke & then a new long rod kit that has been clearanced will be installed in your machined crank halfs to complete a 5mm stroker.
You will need that crank, the proper thickness cylinder base spacer plate, a piston kit & gaskets.
Neil

[robyone]

Will there be any problems with adjusting the porting for the stroker on a PV cylinder that has been ported for low /mid?

[C-LEIGH RACING]

Yes it will.
It will take quite a bit of time to degree the ports in & re-set them because they will be higher in the cylinder than need be.
The head dome will need cutting as well because of the ports being cut, piston will need to go up into the head to make the ports degree out like they needs to be.
Neil

[fireburns99]

sure seems like a lot of work and money to make a stroker work. Wouldn't a big bore cylinder be easier and cheaper?

[C-LEIGH RACING]

Originally posted by fireburns99
sure seems like a lot of work and money to make a stroker work. Wouldn't a big bore cylinder be easier and cheaper?

Yes it would.

Building a stroker engine is just one of the little things that add all up in the end when hunting HP.
Neil

[wilkin250r]

Originally posted by fireburns99
sure seems like a lot of work and money to make a stroker work. Wouldn't a big bore cylinder be easier and cheaper?

There are advantages and disadvantages to each.

But a stroker can be made into a very potent motor. In fact, I heard once that back in the prime of the 250r, pro racers kept the stock bore and they stroked the motor to get the maximum 265cc.

[86 Quad R]

Originally posted by fireburns99
sure seems like a lot of work and money to make a stroker work. Wouldn't a big bore cylinder be easier and cheaper?


but it sure is worth it in the long run. add a larger bore(preferribly a pro-X cylinder) to up the cc's to about 310, get everything setup and dialed in and you'll have your hands full. :devil:

[robyone]

Originally posted by C-LEIGH RACING
Yes it will.
It will take quite a bit of time to degree the ports in & re-set them because they will be higher in the cylinder than need be.
The head dome will need cutting as well because of the ports being cut, piston will need to go up into the head to make the ports degree out like they needs to be.
Neil

So what is the best set up to go with so you don't have to cut into the dome with a low mid ported cylinder?

[86 Quad R]

if i recall right. the best setup for the least amount of head work would be the 4mm crank, 87-89 long rod and piston with a 2mm spacer plate. with this setup you should be in and around the 87-89 piston to deck height. neil, correct me if i'm wrong :confused:

[robyone]

So what kind of cc's would I be looking at with the 4mm stroker and a 70.00mm piston.
I'm trying to decide what would be best, build a stroker for my 275 PV or just sell it and get the 305 PV.