6.5mill spacer?

[sangheraent]

well i was looking into stroker cranks and thinking how big a spacer should be and mine just looked huge. so i measured it and its huge!!
i dont get it why would my bike need such a huge spacer its suppose to be an 89 crank with an 86 cylinder and piston. i had .53 squish band with a stock gasket and ran 160 psi compression. the bike had power was maybe 3 lengths behind piped and jetted yfz450.
http://i609.photobucket.com/albums/tt172/sangheraent/IMG_5478.jpg

Huge spacer for a stock cylinder and stroke…something is not correct here, unless the cylinder base was cut down for some reason. What is your exhaust & transfer timing set at?

.53…? Is that in MM or inches? If it is MM, then it is very tight (.020”) for a squish band clearance and the 160PSI does not fit with a .020” or .53MM squish band, you would expect a much higher compression.

If the .53 is in inches (.530”), and you are saying you have .53” squish band, then the reverse is true, I would not expect you to have 160PSI, it would be much lower.

6.69MM spacer is more what you would find in a large displacement build…Pumashine is the resident “spacer plate” expert, maybe he will shim in…

Carlos.

[Honda 250r 001]

Im betting your cyliner has either a custom piston and port work, or has been milled great ammounts.

“custom piston and port work, or has been milled great amounts”…Agreed.

Could also be the cylinder was part of another previous build by a different owner, and transferred to this relatively stock engine requiring the 6.69MM spacer plate.

Carlos.

[sangheraent]

sorry .053 squish band. its not a custom piston. I know because i bought it from prox as an 86. the head is a standard pro design head with a 19cc dome. 160psi compression and it hauls *** i dont get it?
the cylinder is a 68mm bore LRD MX ported stock cylinder.

.053” squish band, 19CC and 160 PSI, a little low on the compression, however; “OK”…

Sounds like the 6.69MM spacer plate is what it takes to “put back” what was removed from the bottom of your cylinder at one time…

If it “hauls”, then its good!

Carlos.

[sangheraent]

i think you could be right. They take off a little bit to increase bottom end right?

A little yes, 6.69MM I don’t know…

Can you post more information, pictures, port timing…?

Carlos.
:)

[sangheraent]

well heres something interesting. I put it right beside a stock cylinder and well the top of this cylinder is shaved down. i couldnt think of any reason for it to be shaved down I'm stumped.

Are you sure the crank has not been stroked? Possibly a short rod in a long stroke?

Sounds like the cylinder has been raised to increase all port timings significantly, then the top of the cylinder was decked to provide the desired squish clearance. The bottom of your cylinder could also have been decked…

Pictures, port timing, dimensions will get you a much clear picture…

Carlos.

[bndon450r]

My guess Is +4mm stroke with long rod and a 86 piston??? (.190 spacer Normal spacer for Long Rod with 86 piston) + .040 for 2 gaskets= .230 or (4.842 converted to Metric) + (2MM stroke half of 4mm total stroke = 6.842. That could be why they shaved the top possibly? Did It have both gaskets on the top and bottom of the spacer?

[sangheraent]

that makes sense. how would i find out if it is a stroker crank. I know the rod says hot rods on it. i have a 86 stock crank and if the pin is in diffrence places does that mean its a stroker crank?

[bndon450r]

A long rod Is 125MM long, the short Is 120MM measure the rod first, then measure from the crank wheel to the top of the rod I have a stock long rod crank If you want me to measure It.

[sangheraent]

i have a stock 86 crank that i can refer to.

[sangheraent]

it looks identicle to my 86 crank but 5mm longer. the pin on the crank bottom is in the exact same spot on both cranks.

Sounds like you have a long rod crank (87-89) and a 85-86 cylinder & piston. The difference between a long & short rod is 5MM. 85-86 cylinders came with short rods…

If you account for the 5MM rod difference between an 85/86 & 87-89 crank, the 7.69MM (6.69MM spacer + two .5MM gaskets) total spacer height, and assume 2.69MM for the added raised port timing, it makes sense.

The cylinder appears to has been raised to increase all port timings significantly, (inexpensive method of porting) then the top of the cylinder was decked to provide the desired squish clearance of .53MM. The bottom of your cylinder could also have been decked either for clean up or to adjust post heights…

Most likely she is a screamer; high port timings with the longevity of a long rod…

Carlos.

[atv fan 28]

Originally posted by bndon450r
A long rod Is 125MM long, the short Is 120MM measure the rod first, then measure from the crank wheel to the top of the rod I have a stock long rod crank If you want me to measure It.

130.3 long rod, 125.3 short rod.

[Pumashine]

Originally posted by atv fan 28
130.3 long rod, 125.3 short rod.

I was told 130.3mm long rod and 125mm short rod. Actually a 5.3mm difference?

Yes; 130.3MM long rod and 125MM short rod sounds correct…

Carlos.