More power AND better engine life?

crmachineman

crmachineman

New Member
Hi everybody!

Good engine life is very important to us. The last thing we want to see when we take the head off is scratches in the cylinder bore!

When I started developing the new cylinder head for the 66cc. 2 stroke engines, I was looking for maximum power, but when I started running the head, I noticed the pistons and cylinders are not wearing out like they used to!

In the early days, I was very disappointed with how the cylinder walls would get scuffed up within days of operating. That problem is gone! Totally gone! The new cylinder head has ample cooling, it's strong and doesn't warp.

Now, when I take the engine apart, I see a nice oil film on the cylinder and the piston.

Before I ran the new head, I used to take the engine apart and see dry, burnt oil deposits; how can a 2 stroke engine survive that! They can't! I would wager that almost every stock engine is just running too damn hot!

Here is a link to my ebay store, where you can purchase the cylinder heads.

http://www.ebay.com/itm/Motorized-b...Accessories&vxp=mtr&hash=item1e6f5e313d#ht_14

There is a bunch of technical data on the head, and also a bit on the special things you need to do on the GT-5 motor. They put the wrong cylinder on those engines. It's a really good cylinder, but it's too tall!

Thank you!

.duh.

-Fred
 
OK, I would like to use the head as it looks to be a nice piece but I would like to put it on a Grubee "Super Rat Engine". Have you had any experience with that engine/cylinder/piston combo? If not, I could take a digital depth guage and let you know how far down the piston sits in the jug at TDC. Also, wouldn't you need to know how much of a dome the piston has?
 
Hi Fonzie.
That is no problem. I know a little about that engine. Your engine is pretty good to take the head without any modifications. The nice thing about your engine is that it has a good crankshaft (one that doesn't need straightening). And it uses, in my opinion, the best cylinder design yet offered for these engines. Your engine will not have the kind of problems the GT-5 engine has. I think it would be good idea to check where the piston sits when it's at TDC, like you mentioned. If you want to achieve maximum compression, you will want the outer edge of the piston to be as close to the top of the cylinder as possible. The head gasket will then determine the squish clearance. The head is designed to be able to run that kind of compression without having any bad effects.

Oh yeah, and about the radius of the dome top of the piston; They are all the same, including the GT-5 piston. There is some bad information out there regarding that. Your engine runs the same piston that all the 66cc engines use, except for the GT-5, which is the unique from all the others in that it uses a different connecting rod and piston and requires a shorter cylinder, but when they were put together at the factory, they didn't put the right cylinder in, so now, the GT-5 cylinders we got need to be decked about 1 MM to solve that problem.

I also have two SR cylinders in stock, in case you need one decked. According with the measurements I have made, I would probably recommend one decked -.020", but you should check that to confirm.

Thank you very much.
-Fred

brnot
 
Thanks.... I will double check the depth of piston in the jug at TDC and let you know if I need a cylinder as well. I bought a good super rat bottom end and bought a new cylinder and piston from Gasbike that is supposedly for the super rat but it will be easy enough to check.
 
I knew I saw this somewhere. This is a quote from Pirate cycles website about their head-Thats why I asked about the piston dome

"A High Comp Head for the Grubee GT5 engine. This Head works on the GT5 and other motors with the .060 domed piston and only works effectively on the .060 domed pistons. If you use this head on a motor with the .030 piston you will soften your compression, loose power, then wonder why.. These heads do NOT work on the Grubee super rat motor."
 
fonzie said:
I knew I saw this somewhere. This is a quote from Pirate cycles website about their head-Thats why I asked about the piston dome

"A High Comp Head for the Grubee GT5 engine. This Head works on the GT5 and other motors with the .060 domed piston and only works effectively on the .060 domed pistons. If you use this head on a motor with the .030 piston you will soften your compression, loose power, then wonder why.. These heads do NOT work on the Grubee super rat motor."
Click to expand...
Bad info and hopefully a typo.

Should read 0.160 and 0.100

Piston Bikes head is a copy of the original MM "ash tray" head. :)
 
Ok.
Thanks for that correction. I've never seen any of those old engines, and I have not seen any replacement pistons with a different piston dome contour.
-Fred

zpt
 
Oh, and another thing about that Pirate Cycles information. The GT-5SR is not a low compression motor, like the GT-5. That whole description of that head must be wrong! The GT-5 motors are the only low compression motors, yet they say the head is designed for those motors; that just doesn't make any sense. Anyway, that ashtray head doesn't look like it has adequate cooling either. The GT-5 motors were supposed to get what Don Grube calls a "Big hole 68" cylinder body. Instead, they got "Big hole 69" cylinder bodies. Rather than taking them all apart and putting the right cylinders on, they just sent them to us. I have never seen a big hole 68 cylinder body, so I'm just decking the cylinders for people who are running GT-5's. That is the proper way of solving the problem. You can't utilize the benefits of the squish band type cylinder head if the piston is stopping too far away from the combustion chamber, so it is not practical to design a head for the GT-5 motors, unless you deck the jug.

-Fred

.flg.
 
CRMachineman
Thanks for all the info....I just ordered a head and cylinder decked .020. Also sent you a note thru Ebay that it was for a "Super Rat". Just covering all the bases.
Thanks....anxious to see how it works
 
Thanks Fred!
Hey guys.....Fred gets an A+++++++ from me on service, speed of shipping, knowledge of products, and communication! Can't wait to get the head and cylinder.
Clyde Miller(Fonzie)
 
do you manufacture that head in an angle fire config ? I like to build in really tight frames , an what is its over all outter dimensions?
Gary
 
Hi Gary.
I don't have a angle fire head, yet.
I do plan on making a twin spark plug version which will have the spark plugs on each side of the head. It will be a little more expensive because of an additional setup.
The nice thing about this setup is that I will allow me to also make single spark plug angle fire heads as well. Also it will be no trouble for me to orient the spark plug hole forward facing as well.

Back to the twin plug head:
If using twin ignition is not practical, I am thinking of eventually finding or making a decompression valve which will fit in one of the spark plug holes. This would be the other way you could use the "twin plug" design.
So, anyway I will probably have something really great to show you guys in about 2-4 weeks.

My work on the 49 cc head is on hold for the moment; not enough time!

laff

-Fred
 
thegnu said:
do you manufacture that head in an angle fire config ? I like to build in really tight frames , an what is its over all outter dimensions?
Gary
Click to expand...

Oh sorry Gary, I forgot one of your questions.

The outside diameter of the head is 5 inches. The total height is about 2 inches.

-Fred
 
I would definitely buy a head with a crv (compression release valve). My engine is high compression, and even though I have not made any modifications to the engine, it still usually takes two bumps to get it started when cold. How much do you think you would sell a head like that for? my engine is a 68cc engine, not sure of the exact dimensions of the head, but I could measure it if you needed.
 
Yeah, I should be a help for starting, and it can be used for braking from what I understand. I have not done any research on what valves are available or even exactly how to make one, so a little time for that maybe. I really can't say exactly what the price will be, but I'm thinking that it will probably be another 10-20 dollars in additional cost over the current one I'm producing.

About what kind of engine it will work for:

Well, it will be designed for the common Grubee 66/80 cc engines you find all over the place. And the engine will need to have 8 MM studs.

-Fred

.duh.
 
I just discovered that another vendor has stock rechambered high comp heads for $35. cant beat that, so I will be picking one of those up.
 
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