Thatsdax new GT5 geometry engines

[mapbike]

Just wanted to report that I received the two GT5 "type B" 38mm stroke lowers I ordered from thatsdax last week, he was kind enough to add a couple extra parts in the package which was very nice of him to do, the engines look good, I'll have to do some closer comparison to see for sure but it does look as though the transfer passages in the case may be a bit smaller than those in the older GenIV 40mm stroke engines, the casting is a bit rough around edges of transfer areas but nothing that cant be smoothed up easily, the cranks spin a bit tight in both lowers but I've seen the same thing in others and hasn't ever created any issues in my other engines, that tightness goes away quickly after engine is run a few minutes, nothing rough feeling during rotating just a bit tight.

I'm gonna try to get one of these together and on a bike asap so I can honestly report what the balance is like and what I think of the performance that can be expected with just a few basic mods which will be mainly cleaned up ports and I will most likely use a PK80 cylinder that has had the deck shaved to a good height for the Puch 70cc Hi Hi head I plan to use on it.

It is possible that I will just clean up and mod the small port jug just to see what I get from it, but I just don't think good top end speed is gonna be achieved with one of these jugs that have extra small ports in every area.

I may put some very small ramps on piston at transfers if the ports on the jug I use aren't as open at BDC as I would like them to be.

My old Black mountain bike that has the horribly balance old BGF engine on it will be the likely candidate for one of these, it has never seen 40MPH and that is what I will be shooting for, not looking for a 10,000 RPM engine, just something that will be comfortable to ride mid 30's to 40mph when I hit the open road 10-12 miles into town now and then.

Pics below are of the GT5 dax lower, post that will follow this one will be of the jug.

 

[mapbike]

GT5 small port jug link

I decided to put this post in the correct area to save the mods the trouble of needing to move it.

http://motorbicycling.com/showthread.php?p=597773#post597773

 

[bluegoatwoods]

It's a nice looking crankcase and connecting rod.

Is it a light bronze color or is that just the lighting?

 

[cannonball2]

Does the rod still have the two thrust type washers on either side?

 

[mapbike]

The rod is the Bronze color like most all but the Z-L rods, has the oiler holes drill on piston end also.


No these dont have the extra thrust washers like the older GenIV had, the side to side of the rod is very minimal on each of these two I have though.

That is one point that Duane made when I spoke with him over the phone, he told me that these 38mm stroke engines didnt have the thrust washers, but he also told me the side to side movement was less than many of the engines without the spacers and this seems to be the case just as he said.

Im super curious to see what the balance of these are compared to the Gen IV engi es I have, Duane said that these are just as good so I have high hopes they will be, if not Ill be very disapointed.

 

[maniac57]

Are the case bolts under the clutch replaced as well?

 

[mapbike]

just got them today b3fore i left for work so i havent had a chance to take into one of them yet, but I'll sure post the answer to that as soon as I get a cover off oneof them which will probably be Friday.

 

[Davezilla]

They do look a lot like the Gen IV engines he's been selling and like they're well built from what I can see so far... The tightness in the bearings is a good thing and will go away after it's been run a while, most of it's the preservative oil or grease in the bearings but the gas/oil mix quickly washes that stuff out and protects the bearings from corrosion from that point on after the engine has run. The bronze color on the rods is a copper or bronze plating for the same reason, to protect it from corrosion when not in use for long periods of time such as the normal rider who rides during the summer months then stores the bike all winter, some light surface rust can form in humid environments which can then shed off and get into the bearings etc if it was run without removing this thin layer of light rust, which is like putting sandpaper in your bearings. This isn't needed in a 4 stroke engine, but on a 2 stroke where the piston is up and the intake port is open then let it sit for several months and this rust can form if enough oil is shed off the rod.