Crankshaft Strokes 250, 360, 390, 420, 430, 500cc

[Bigbill]

Just some talk about strokes, I learn all the time here.

250 is 64.5mm stroke,
360 is 67mm stroke.
390 is 71 mm stroke
420 is 71mm stroke.
400 is 74mm stroke similar to the 430 lq
430 is 74mm stroke ac/lq
500 is 84mm stroke. Ac/lq

Correct.?

I picked up a mid to late 70's crankshaft. It has a larger taper shaft on the ignition side like a 360/390. The seller called it a 250, was there a 250 that used a larger 360/390 flywheel? I'm trying to figure out what it is
.

 

[grouty]

Measure the stroke Bill. That will give you a good indication as to what it is. The seller may have thought it was a 250, but ......

 

[jimspac]

The edge of the con rod is more than 1/4" from the edge of the crankcheek on the 250 crank. I am not sure if the 360 has the cheek or lug crank like the 390.

The 1976 250WR and 360WR both had FEMSA point ignition. That could account for the large stub. So like Grouty just said, measure the stroke. You can check the distance between the crank center and con rod center with a vernier or even a scale. Multiply result by 2. If using SAE measurement divide calculated result by 25.4 to convert value to millimeter

 

[grouty]

The 360 had a full circle crank, the 390 had a counter weight crank.
Not sure about the 250's.

 

[Bigbill]

If the 250 came with that bigger flywheel it should be a mountain climber with that mass on the crank.

If it's a 360 crank using a base gasket spacer with a 250 cylinder makes the bore and stroke somewhat boxed. They say when the bore size and stroke is close to each other these engines run better?

 

[wrx]

under square vs over square.

 

[jimspac]

The 360 had a full circle crank, the 390 had a counter weight crank.
Not sure about the 250's.

250s have full circle

 

[Bigbill]

I just found a crank that looks like a 430 crank but the rod is copper plated. Maybe a after market rod?

 

[grouty]

Sounds aftermarket. Probably copper plated when it was heat treated.

 

[fran...k.]

"
250 is 64.5mm stroke,
360 is 67mm stroke.
390 is 71 mm stroke
420 is 71mm stroke.
400 is 74mm stroke similar to the 430 lq
430 is 74mm stroke ac/lq
500 is 84mm stroke. Ac/lq

Correct.?
"


The 250 changed with time. The 87-88 has a longer stroke than the ones just before that, not sure about the ones way before that. There is an earlier 400 than the one in the 84-88 range not sure about that.


430 auto crank looks different than standard shift one as likely some other auto displacement ones.

I do not think any of the ones in the list above is stroke longer than bore perhaps called undersquare. 72mm is what two cycle 250cc bikes seem to have for the last 20 or perhaps more years.

fran

 

[Kartwheel68]

I picked up a mid to late 70's crankshaft. It has a larger taper shaft on the ignition side like a 360/390. The seller called it a 250, was there a 250 that used a larger 360/390 flywheel? I'm trying to figure out what it is
.

Many Huskys used FEMSA points ignitions, any bike with that ignition had the large taper crank snout. My 76 250WR has that large taper crank snout, from then on I think all 250s had the medium taper.

 

[jimspac]

"
250 is 64.5mm stroke,
360 is 67mm stroke.
390 is 71 mm stroke
420 is 71mm stroke.
400 is 74mm stroke similar to the 430 lq
430 is 74mm stroke ac/lq
500 is 84mm stroke. Ac/lq

Correct.?
"


The 250 changed with time. The 87-88 has a longer stroke than the ones just before that, not sure about the ones way before that. There is an earlier 400 than the one in the 84-88 range not sure about that.


430 auto crank looks different than standard shift one as likely some other auto displacement ones.

I do not think any of the ones in the list above is stroke longer than bore perhaps called undersquare. 72mm is what two cycle 250cc bikes seem to have for the last 20 or perhaps more years.

fran

The 500 2T is considered square with a bore of 86mm and stroke of 84mm.