45cc rovan case/cylinder matching technique

[Mr. Marmot]

Hi. So the rovan 45cc cylinder transfer ports and crankcase don't match (no discussion there). What is better for matching them: to jb weld the case or to enlarge the cylinder transfer ports?

If you have to make 3D shapes with jb weld (like in the crankcase) , how do you do it? Or do you use the jb putty?

Thanks

 

[HXRC]

The answer is both.
I use the original liquid JBweld

 

[jeepfreak1972]

I've only ported chainsaws and only for a hobby, so take that that for what its worth lol. I would enlarge the lower transfers to match the case depending on how far off they are. If you hog out too much, without other modifications, you can make an engine lazy. It slows the velocity of the charge going up the transfers because of increasing the case volume. Grinding the lowers increases the case volume. It's a balancing act.

 

[jeepfreak1972]

Are you doing any other modifications like cutting the base and squish band? Or a base gasket delete? Lowering the intake? Widening exhaust? Upper transfer work?

 

[one2boost]

I have a few of these 45s. I did these a bit different. I opted to ramp it and take the basic shape of the cylinder for more of a direct airflow. As compared to the original design, too many areas to obstruct the air flow. I taped off the area of the transfer port area on the case. I didn't use the putty style of JB Weld. I used the conventional standard JB Weld and used a syringe to fill the void. I flattened the case deck, applied Dykem Blue and scribed the shape I wanted. Then went crazy with the Dremel and other tools.

 

[Mr. Marmot]

Thanks. No mods yet. Just figured out that the stock cylinder/case match is so bad that I need to do something about it. The squish is also pretty bad, like 1.7mm with the gasket on, I will have to remove it (but still not good enough). The thing vibrates like crazy, any specific reason for that?

 

[one2boost]

I'm not sure which version you have. Like I mentioned I have a few. There were 2 versions of the cylinder heads;
v1, had a larger exhaust port piston side. When messing with the case deck/base and/or cylinder deck/base, it's easier to freeport.
v2, had a smaller exhaust port piston side.

Pistons also had differences over the years'
v1, single piston ring with domed piston top. Great for achieving a higher compression/tighter squish band.
v2, dual piston ring with domed piston top. I don't have this version as I remember seeing these for sale.
v3, dual piston ring with a flat piston top.

If one will attempt this, scuff the case with some coarse grit sand roll and clean the area for the JB Weld have a better chance to adhere to the case.

 

[Mr. Marmot]

I'm not sure which version you have. Like I mentioned I have a few. There were 2 versions of the cylinder heads;
v1, had a larger exhaust port piston side. When messing with the case deck/base and/or cylinder deck/base, it's easier to freeport.
v2, had a smaller exhaust port piston side.

Pistons also had differences over the years'
v1, single piston ring with domed piston top. Great for achieving a higher compression/tighter squish band.
v2, dual piston ring with domed piston top. I don't have this version as I remember seeing these for sale.
v3, dual piston ring with a flat piston top.

If one will attempt this, scuff the case with some coarse grit sand roll and clean the area for the JB Weld have a better chance to adhere to the case.

Great explanation for the 45cc versions. Didn t know there were so many. Thanks. My piston is double ring and flat. The squish is 1.8mm (really bad) and the gasket is 1.05mm. I think I can take it out and put grey rtv or permatex #2 to get around 0.7mm squish, hopefully.