What is the difference between the Thunder Tiger Pro and GP? From what I know the GP is a plain bearing engine while the Pro is a dual bearing. You might expect the Pro to be a better engine but the GP is of higher power and lighter than the Pro. To top it off, it cost less. It seems like the GP is an obvious choice over the Pro but am I missing something or is the Pro all marketing hog wash.

In most cases, the PRO has much more Power than the GP. The exception is with the PRO 61 and the GP 65. These two are about the same.

Enjoy,

Jim

Depends upon which engine size you are discussing. In this case it sounds like you are talking about the 61 engines, and as w8ye said, there isn't much between them. The Pro is a bit stronger at high revs & the GP is a little happier pulling a big prop.

Being a plain-bearing engine, the GP potentially has a longer lifetime.

However, they are both good (quite a bit better than their respective OS competitors), so you can't lose either way.

In the case of the smaller sizes, the Pro series engines are seriously more powerfull than the respective GP alternatives.

In addition to the bushing vs bearing difference, the GP series has air bleed carburetors and the PRO series has dual needle carburetors. I don't have enough experience to know how significant the carburetor difference is. My engines all have the dual needle design.

I have read that bushing engines need more castor oil in the fuel than ball bearing engines but I have no idea if that is fact.

My brother had a GP42 that ran great. It had a nice slow idle and probably would have idled for an hour if you wanted it to. It transitioned well and ran nicely at all throttle settings. He donated it to the club to go on a trainer.

If the engine is used in the normal manner with the usual props and not mounted inverted, the air bleed is more trouble free than the twin needle carb.

But in special situations, The twin needle is more flexible.

Generally the airbleed carbs are smaller than the twin needle ones.

Enjoy,

Jim

Since journal bearings rely on a lubricant film to "float" the crankshaft, anything that increases the lubricant film strength is a good idea -- & castor increases the film strength. They require more lubrication than a ball-race bearing, but properly designed & installed journal bearings have an almost infinite potential lifetime.

The big risk to BB engines is rear crank-bearing failure -- that will shed chunks of metal into the crank-case, which get sucked up into the cylinder -- often with terminal results. It is not a case of IF the ball bearing fails, it is a case of WHEN it fails. No such problem exists with journal bearings.

Additionally, depending on the bearing material & lubricating fluid, journal bearings are capable of tollerating extremely high rotational speeds -- far higher than any ball-race bearing.