head and port clearence for 4 mill stroker

[gmctruck1976]

Hi Ok not completly ready to do this yet but have got the part together. Im building a 4 mill stroker.

It will be useing 110 mm rods instead of the 115 rods. And ive got a phathead with 21 cc cut domes for a stroker. with stock port I "think"

I dontknow if i need to use this stroker plate or or not. the domes are all ready milled the 2 mill for the stroke, but with these new heads not sure if i need a copper gasket or not for the seal.

im also wondering about the ports at stock do i need the plate for timing issues. or does have to be ported when not using the plate. Last thing is the skirt of the piston. im useing the vitos superstock pistons 65mill bore or 40 over is this going to end up being an issue for me or should i get 21cc none cut domes and run the plate very concerend about this. ive built a few 2 stroke but this is the first stroker ive contended with. so its kinda of a new playing field to work in Ive done alot of research on doing this. every ones got somay vering oppinions on it.

it would be helpfull to know what to look for when finally getting to putting the jugs and head back on.

what issues can arise if i just run the cut domes no plate and stock port? Is this thing just granade on the first sign of combustion.

Im pretty sure im going to get "send it to a builder" awnsers, but honestly want to finish this one on my own. thanks for checking this out

[jbooker82]

Most people will agree that the best way to build a 4 mill stroker is to run domes cut for the stroker crank, and no spacer plate, and have it ported for the 4 mill with cut domes.

 

A 4 mill stroker crank allows the piston to drop 2mm farther down in to the jug (BDC) and it aslo pops out of the jug 2mm (TDC). That is why your domes are machined 2mm for for the stroker crank.

 

You can check this clearance. Put the motor together with no spacer plate and your cut domes. Bend a pice of Solder in the shape of an L, Stick it down through the plug hole so it touches the side of the cylinder. Roll the motor over by hand with the kicker. It will smash the solder. Then measure the solder's thickness where it was smashed. Most people shoot for .035-.040. When you stick the solder in to the cylinder make sure you go parallel with the wrist pin. If you do it over by the exhaust port or intake port the piston could rock a little in the bore causing an inaccurate reading.

 

As for the port timing. When you run no spacer plate with no porting the piston is still going to go 2mm down past the ports. Add that 2mm spacer plate in there now the piston is going to be going down 4mm past the ports.

 

The 2mm spacer plate will advance the timing of the exahust port. A raised exhaust port does help top end power. If you ran no spacer plate it will lower the exhaust port, giving better bottom end. I would run no plate. That way all the stock porting is working together. I however wouldnt plan on keeping it this way. I would get the jugs ported. It will run fine with no problems not being ported. It just wouldnt run as hard as it could. Same is also true for a stock ported, stock stroke banshee.

 

josh

[gmctruck1976]

Most people will agree that the best way to build a 4 mill stroker is to run domes cut for the stroker crank, and no spacer plate, and have it ported for the 4 mill with cut domes.

 

A 4 mill stroker crank allows the piston to drop 2mm farther down in to the jug (BDC) and it aslo pops out of the jug 2mm (TDC). That is why your domes are machined 2mm for for the stroker crank.

 

You can check this clearance. Put the motor together with no spacer plate and your cut domes. Bend a pice of Solder in the shape of an L, Stick it down through the plug hole so it touches the side of the cylinder. Roll the motor over by hand with the kicker. It will smash the solder. Then measure the solder's thickness where it was smashed. Most people shoot for .035-.040. When you stick the solder in to the cylinder make sure you go parallel with the wrist pin. If you do it over by the exhaust port or intake port the piston could rock a little in the bore causing an inaccurate reading.

 

As for the port timing. When you run no spacer plate with no porting the piston is still going to go 2mm down past the ports. Add that 2mm spacer plate in there now the piston is going to be going down 4mm past the ports.

 

The 2mm spacer plate will advance the timing of the exahust port. A raised exhaust port does help top end power. If you ran no spacer plate it will lower the exhaust port, giving better bottom end. I would run no plate. That way all the stock porting is working together. I however wouldnt plan on keeping it this way. I would get the jugs ported. It will run fine with no problems not being ported. It just wouldnt run as hard as it could. Same is also true for a stock ported, stock stroke banshee.

 

josh

Just wanted to say thanks for this post. I wasnt sure the correct way to go with this set up. Your post was a grate help. The set up i was planning was cut domes no plate. Ive been trying to set up a good running trail runner with a little bit of hair scrambles mx mix. im trying to shoot for 50 to 60 hp hope this set up will get it there. trying to build a bottom end ride anyway

[jbooker82]

Glad I can help. Just make sure to check the clearance with the solder. That is your squish clearance.