Gravy
Platinum Member
After 5 years and approaching 600 hours of hard use and abuse, along with several catastrophic air filter failures in extremely dusty conditions, the Robin EH72D 720cc/25hp engine in my PT425 has just about had enough. The blow-by is now overwhelming the additional crankcase breather separation/filtration system that I added last year. I also cranked up the governor to a maximum speed of somewhere between 3800-4000 rpm to compensate for lost compression. (It was out of warranty, and I needed the power...)
I don't think a rebuild is practical. The engine has ingested a lot of dust, and I suspect the wear is systemic. Also, it's snow season, and disabling the PT for more than a few days could be a problem - we have a long driveway.
On top of that, there are some improvements I'd like to make over the original Robin engine: I want MORE POWER! I also want less noise and much better fuel efficiency. (My employer has a Cat 416C backhoe that weighs on the order of 10 times what my PT425 does, and can lift and dig proportionally. It does all that while using LESS fuel per hour than my PT.)
I'm starting to look at replacement options. There are a bunch of choices for replacement engine. There are two that a pretty much no-brainers:
1: An exact replacement Robin EH72D. Pros: Exact fit with no worries. Cons: It was underpowered, excessively noisy, and a fuel hog from the factory.
2: The new Robin fuel injected EH72FI. Pros: Probably exact fit, since it's the same basic engine with the addition of EFI. Also, it's rated to run at 4000RPM with an increased HP rating. Cons: The claimed power and fuel efficiency improvements are pretty trivial (maybe 4-11%). Also, the ECU is incorporated in the throttle body, which leads to concerns about heat and vibration damaging the electronics. In addition, I haven't seen any claims of noise reduction.
Those are the easy ones. After that it gets complicated. Honda, Kohler, Briggs, Generac and Kawasaki all offer a range of air-cooled V-twins, some of which *might* physically fit. Some of them are fuel injected. Some have greater displacement, some have higher compression ratios. Some have extra noise controls.
But wait, there's more! Even on the basics, comparing apples to apples isn't easy. Some manufacturers quote "SAE Gross" or "maximum" HP & torque specs. Others quote "SAE Net" specs, which always give lower numbers for the same engine. (Not to mention DIN or ISO specs).
So aside from the implied rant, I do have an actual question: Does anybody know of a replacement engine that will be an overall improvement? If I have to, I will buy an exact replacement, but I'm really hoping for better.
Anybody got a spare "Mr. Fusion" laying around?
I don't think a rebuild is practical. The engine has ingested a lot of dust, and I suspect the wear is systemic. Also, it's snow season, and disabling the PT for more than a few days could be a problem - we have a long driveway.
On top of that, there are some improvements I'd like to make over the original Robin engine: I want MORE POWER! I also want less noise and much better fuel efficiency. (My employer has a Cat 416C backhoe that weighs on the order of 10 times what my PT425 does, and can lift and dig proportionally. It does all that while using LESS fuel per hour than my PT.)
I'm starting to look at replacement options. There are a bunch of choices for replacement engine. There are two that a pretty much no-brainers:
1: An exact replacement Robin EH72D. Pros: Exact fit with no worries. Cons: It was underpowered, excessively noisy, and a fuel hog from the factory.
2: The new Robin fuel injected EH72FI. Pros: Probably exact fit, since it's the same basic engine with the addition of EFI. Also, it's rated to run at 4000RPM with an increased HP rating. Cons: The claimed power and fuel efficiency improvements are pretty trivial (maybe 4-11%). Also, the ECU is incorporated in the throttle body, which leads to concerns about heat and vibration damaging the electronics. In addition, I haven't seen any claims of noise reduction.
Those are the easy ones. After that it gets complicated. Honda, Kohler, Briggs, Generac and Kawasaki all offer a range of air-cooled V-twins, some of which *might* physically fit. Some of them are fuel injected. Some have greater displacement, some have higher compression ratios. Some have extra noise controls.
But wait, there's more! Even on the basics, comparing apples to apples isn't easy. Some manufacturers quote "SAE Gross" or "maximum" HP & torque specs. Others quote "SAE Net" specs, which always give lower numbers for the same engine. (Not to mention DIN or ISO specs).
So aside from the implied rant, I do have an actual question: Does anybody know of a replacement engine that will be an overall improvement? If I have to, I will buy an exact replacement, but I'm really hoping for better.
Anybody got a spare "Mr. Fusion" laying around?
