Need power? had to raise cylinder .095"(2mm+)

[socalscott]

Plagued with chronic weak power?

The cause is likely to be that the cylinder is sitting quite low.

Contacted Bob of North Tahoe MotorSports. He wasn't surprised when my concerned brother ask about raising the cylinder/ports .095". Bob said he was on the right track and that he can provide custom gaskets of .035" and .057". Well now, that's .092" init.

My brother also found that the case/cylinder base was a poor match. He had to remove 3/16" from the cases!

Yee-haw, this thing rips now and easily pulls 6th gear with authority despite a 13/44 sprocket set. The 44 was the previous owners solution for an extremely short p/b. He said it was for the dez. Just got a 12T c/s and a G2 throttle.

Check yours by removing the head and cranking the piston down to BDC. Look down into the transfer(side) ports to see where the top of the piston is in relation to the bottom edge of the port. It should be even with it.

 

[AZRickD]

What the FARC?

 

[EricP]

Lately I have seen a lot of talk of the cylinder being to high or too low. How do you know if it is at its correct height?

 

[2 strokes 4 life]

Why not just adjust the head squish?

 

[PEB]

Adjusting the squish would not move the piton in relation to the ports, something I thought the factory got right, but not according to socalscott. Tell us more Scott.

 

[socalscott]

Well, as I mentioned. According to Bob of North Tahoe Motorsports 'we are on the right track'. Did I mention he sells the thick set of gaskets?
BTW, He also mentioned getting the squish gap down to .051" or .052" is a good idea.

I'll defer to Bob.
http://stores.ebay.com/NORTH-TAHOE-MOTORSPORTS_W0QQcolZ4QQdirZ1QQfsubZ0QQftidZ2QQpZ2QQtZkm

 

[101racing]

How good is this bike off the bottom ? This whole deal that you have done raised the port timing considerable and I would think that the bottom power would be sacrificed. Have you had it on some tight trails yet ? Thanks

 

[widebear]

There is more on this from Scott in the general discussions.

 

[socalscott]

How good is this bike off the bottom ? This whole deal that you have done raised the port timing considerable and I would think that the bottom power would be sacrificed. Have you had it on some tight trails yet ? Thanks

Crawled up some step, technical climbs with no sign of weak bottom.

 

[iancp5]

What are you guys riding that makes you want more top end?
Desert?

My 300 would hit 70 mph (13/48) and pull strongly on the way. Here in the UK there was only 1 event where I had it tapped out. I'd guess most I do we never exceed about 50 mph and average speeds are closer to 15 mph! We do have some Rally type events in the forests that have lots of fast fireroads but to be honest I get queezy above 60 mph looking at steep drops off the side of bends with trees and tree stumps everywhere! Occasionally people go over the side and it never ends well. Usually they lay them down first or they'd sail so far out they'd have a few hundred foot drop at 70 mph.

 

[widebear]

port timing specs

The cause is likely to be that the cylinder is sitting quite low.

Contacted Bob of North Tahoe MotorSports. He wasn't surprised when my concerned brother ask about raising the cylinder/ports .095". Bob said he was on the right track and that he can provide custom gaskets of .035" and .057". Well now, that's .092" init.

You guys are getting off easy.Just did a preliminary measurement on the mc 250 prior to splitting the cases. Looks like I need to raise the cylinder 0.11 inches to get the transfers and exhaust port to completly open, hope to get the degree wheel on in the next few days for some port timing specs.

 

[Hollywood]

The cause is likely to be that the cylinder is sitting quite low.

Contacted Bob of North Tahoe MotorSports. He wasn't surprised when my concerned brother ask about raising the cylinder/ports .095". Bob said he was on the right track and that he can provide custom gaskets of .035" and .057". Well now, that's .092" init..

[You guys are getting off easy.Just did a preliminary measurement on the mc 250 prior to splitting the cases. Looks like I need to raise the cylinder 0.11 inches to get the transfers and exhaust port to completly open, hope to get the degree wheel on in the next few days for some port timing specs.

This is not good....

 

[widebear]

I'm sure its not a huge deal as the port width may be more important than its height in how a engines power characteristics are going to be exhibited. Correcting it is going to effect how many degrees of crankshaft rotation the the port window remains open as well as its effects on scavaging. Pipe choice and designe in conjunction with higher pressure and higher volume of the mixture due to the larger port area and its effects of pumping. Lots of engineering and math thats beyond my ability. I'm not up to in predicting the changes in a academic sense, but obviouslly I feel strongly enough that the efforts will be worth it and end results will be positive. As Ive stated before the gasser is a world market, ( say fuel quality) enduro bike and I believe the engineers have very sound reasons for setting them up in a softer state of tune. Besides for the price of a head, like they say, no guts no glory!

 

[widebear]

From my friend chad

http://bluemountainmotorcycleclub.com/forum/showthread.php?t=771