Over-bores, strokers and reliability

I'm just digging into the world of big bore kits, and I have some simple questions about the reliability of bigger displacement kits.

Over-bore kits appear to come in +4, +5 and +5.5 mm. Can you go as far as +5.5 mm and still have commuter-level reliability? From what I've read on TT, you can with a +4, but what of the bigger bores?

Also, I've read that some strokers require a piston so light that it has less rings on it, and it is therefore prone to wear quickly. Is that right? Is it true of all strokers?

And if you want to give specific advice: I of course want more power, but don't want to sacrifice stock reliability for it, and want to spend as little as possible.

Oh, and finally, are new cams requisite with a big bore kit? Or can they be put off until later?

Anything over +4mm bore and you'll have head gasket sealing issues.

They are quite reliable.

Stock cams in a bored and stroked motor is not going to breath well. My big block with Hotcams is getting stroked. I've sold the cams to get a set of Ron Hamps cams. That necessitates valves and springs...just to keep it reliable

HotRods stroker piston is a single ring piston. Not good...but you don't need a spacer plate under the cylinder. I'd rather have the spacer and two rings...

J&E pistons need to have the skirt trimmed to clear the crank or it will hit. CP makes a 94mm piston with a shorter skirt that will require no machining. The J&E weighs 304 grams and the CP weighs 280.

You "Can" wait to cam it later but you won't make any power. And you need to degree the cams anyway (slotted sprockets) if you use a spacer plate. I'd just do it all at once. In fact...I am.

Waiting to cam a stroker is not a good idea. With that kind of cylinder pressure...huffing the head gasket is a real possibility...according to Eddie. The RHC cams have more overlap and bleed off the excess pressure.

I did initally run my 475 with the stock cams. The performance gain was not that impressive. It got impressive after upgrading the cams and Installing the MRD-SSW exhaust. Now it is a rocket ship.

my 470 stroker is a +4mm bore and +5mm stroker crank.i have all the goodies to make it a 50+hp beast.ive run it all year and have had no reliability issues.just the normal issues of your friends that bought huskies and ktms not wanting to ride with you after you blow there fenders off with a drz:busted:

oh ya im using a je 3 ringer(including the oiler rings)piston with a spacer plate

reliability.........

what is your power goal? a 47-50hp drz is just as reliable as stock.thats +4mm bore,hotcams,39mm fcr and mrd/ssw pipe or yosh ti.

big bores...........

on a stock cylinder being made into to a big bore i highly suggest +4mm as the limit. using an athena cylinder as a base they are safe to 96mm.the ice cube cylinders also will work at bigger than +4mm but are very expensive.

stroker cranks.........

hotrods released a +4mm stroker crank that doesnt use a special piston or mods or a spacer that the +5mm required.this makes building one a little cheaper now because of that. you save the money on the cylinder spacer and you dont need the $180 adjustable sprocker kit for the RHC cams.we have them ground to correct lobe center for stock deck height motors.if you want to vary the cam timing you would need them but otherwise they alwasy come in within 1 degree as long as the cam chain is good.not using the cylinder spacer also negates any issues that arise from raising the motor height 2.5mm (motor mount slotting,pipe to rad clearance,etc).

cams..........

stock stroke motors work well with the hotcams stg 1 cams.

stroker motors use the RHC cams that we had specifically made for the purpose.they are about $75 difference in price.

carbs........

39 vs 41mm. stock stroke motors used for all around riding work best with a 39mm fcr.sm race motors or bikes that see lots of track days the 41mm does offer some gian at high rpm.

stroker motors work best with the 41mm fcr unless used for off road work exclusively.for off road use a 39mm is better but i wouldnt want to ride a 50+ hp drz off road. it will jsut make you tired.

hotrods released a +4mm stroker crank that doesnt use a special piston or mods or a spacer that the +5mm required.this makes building one a little cheaper now because of that. you save the money on the cylinder spacer and you dont need the $180 adjustable sprocker kit for the RHC cams.we have them ground to correct lobe center for stock deck height motors.if you want to vary the cam timing you would need them but otherwise they alwasy come in within 1 degree as long as the cam chain is good.not using the cylinder spacer also negates any issues that arise from raising the motor height 2.5mm (motor mount slotting,pipe to rad clearance,etc).

Really Eddie?! Now I'm interested in a stroker motor. At first I didnt want to go 470 as the cost was a bit high. With a 434cc kit and a +4 crank, what would the final displacement be? Hmmm, the +4 seems to be an interesting option.

reliability.........

stroker cranks.........

hotrods released a +4mm stroker crank that doesnt use a special piston or mods or a spacer that the +5mm required.this makes building one a little cheaper now because of that. you save the money on the cylinder spacer and you dont need the $180 adjustable sprocker kit for the RHC cams.we have them ground to correct lobe center for stock deck height motors.if you want to vary the cam timing you would need them but otherwise they alwasy come in within 1 degree as long as the cam chain is good.not using the cylinder spacer also negates any issues that arise from raising the motor height 2.5mm (motor mount slotting,pipe to rad clearance,etc).

Do they use a 4mm shorter rod? I guess they have to if the don't move the wrist pin. Do you know the street price of the crank? I may build up the extra bottom I have.

With a 434cc kit and a +4 crank, what would the final displacement be?

462cc

Do they use a 4mm shorter rod? I guess they have to if the don't move the wrist pin. Do you know the street price of the crank? I may build up the extra bottom I have.

yes,shorter rod.

the crank is $375 msrp i believe.

Really Eddie?! Now I'm interested in a stroker motor. At first I didnt want to go 470 as the cost was a bit high. With a 434cc kit and a +4 crank, what would the final displacement be? Hmmm, the +4 seems to be an interesting option.

unless someone really wants a +5mm i will be using the +4mm from here foward.

it lowers the price of the motor about $300.

still not cheap to build but these days everything helps.

if you want a quote pm me yout current bike set up and what you will be using the motor for.

for most people a 436cc motor is the best way to go.

Sounds great. After thinking it through I think I'll be just fine with a big bore kit. As my daily ride, I'd just like my SM to be quick and not "fast". Porting the head of a big bore may be an option, of course then I'd be shipping it to you for you to work your magic.

Do you know how much of a hp gain you may get from porting on a drz with an 3x3/fcr39/cams/434/sswmrd? That may just bring it up past that 50hp mark.

462cc

It should be like this ?

std bore 90.0 x stroke 62.6 mm (formula π x r2)

400 = 45x45x3,14x62,6 = 398cc

434 = 47x47x3,14x62,6 = 434,20

4mm stroker + 4mm overbore = 47x47x3,14x66,6 = 461,95

5mm stroker + 4mm overbore = 47x47x3,14x67,6 = 468,89

Interesting...didnt know that hotrods came out a +4mm stroker crankshaft too..So by using this setup, there's no need for the spacer plate and modfication to the piston. How will the base gasket setup be if I want to stick to pump gas?

i have + 5mm stroker , 94 mm JE piston with spacer , RHC cams & valves & springs , mild porting , 41 mm FCR .

full dirt use for 2 years with no issues . use quality oil , quality air cleaners , the full motor kit is rock solid reliable

for most people a 436cc motor is the best way to go.

Just to confirm, that's a +4 mm overbore and no stroker, right?

Just to confirm, that's a +4 mm overbore and no stroker, right?

yes ..

Hey Eddie,

Just wondering what you would rate the difficulty of a stroker conversion out of 10.

From the sounds of things the ease of the new +4mm crank makes it sound like it could be done at home (obviously with the right tools etc.)?

I've never done this much engine work myself before - but I'm looking for a project bike and the appeal of the stroker conversion retaining commuter reliability is making it a very attractive option.

Was already going to do the big bore and carby install myself as that stuff seems fairly straight forward considering my experience... just want to know how much more work/difficulty the next step would be as I've never gone that far...

Sorry if it seems like a noob question. Just want to do as much labour myself as possible - but not if its so difficult I could risk permanent damage to the engine.

Thanks,

Marc

It should be like this ?

std bore 90.0 x stroke 62.6 mm (formula π x r2)

400 = 45x45x3,14x62,6 = 398cc

434 = 47x47x3,14x62,6 = 434,20

4mm stroker + 4mm overbore = 47x47x3,14x66,6 = 461,95

5mm stroker + 4mm overbore = 47x47x3,14x67,6 = 468,89

Yes, that's correct.

Sounds great. After thinking it through I think I'll be just fine with a big bore kit. As my daily ride, I'd just like my SM to be quick and not "fast". Porting the head of a big bore may be an option, of course then I'd be shipping it to you for you to work your magic.

Do you know how much of a hp gain you may get from porting on a drz with an 3x3/fcr39/cams/434/sswmrd? That may just bring it up past that 50hp mark.

the stock head supports 55hp.

in order to see real gains on a 436cc motor with porting you would need the RHC 187 cams (and related valve train parts) and a 41mm fcr. full on SM race motor this would work welll.street motor or off road it will be too peaky.

at that point you are a $375 crank away from having the 462 motor.

Hey Eddie,

Just wondering what you would rate the difficulty of a stroker conversion out of 10.

From the sounds of things the ease of the new +4mm crank makes it sound like it could be done at home (obviously with the right tools etc.)?

I've never done this much engine work myself before - but I'm looking for a project bike and the appeal of the stroker conversion retaining commuter reliability is making it a very attractive option.

Was already going to do the big bore and carby install myself as that stuff seems fairly straight forward considering my experience... just want to know how much more work/difficulty the next step would be as I've never gone that far...

Sorry if it seems like a noob question. Just want to do as much labour myself as possible - but not if its so difficult I could risk permanent damage to the engine.

Thanks,

Marc

imho its past the skills of most hobbyists.

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