Al
Guru
- Joined
- Apr 1, 2012
- Messages
- 2,206
- Location
- usa
- Vessel Name
- 'SLO'~BELLE
- Vessel Make
- 1978 Marben-27' Flybridge Trawler(extended to 30 feet) Pilothouse Pocket Cruiser[
Greetings.
Within the last couple of days an interesting issue regarding the discussion of ‘Over Propping’, WOT, and such became relevant.
The subject has several threads in history, yet this I believe, is a different approach to the subject as a whole with a specific point.
A couple of weeks ago while diagnosing a different issue, [Why did the tachometer not register with the engine running] for a future subject, the young mechanic noticed that my fuel injector pump housing was damp with leaking fuel. Not bad or dangerous, but noticeable. I then stated that within the last couple of outings, the throttle idle had dropped from the normal 550 down to 200 or less. Everything ran well, there was not concern with the range of throttle while underway, that the idle had dropped without any adjustment was nagging.
The mechanic indicated that there were springs within the pump and that the drop without any physical involvement happened and the pump was showing leakage perhaps a re-build of the pump was in order.
With the time frames involved with removing, shipping, re-building, shipping back and reinstalling, I decided to search out a rebuilt pump or new depending on cost. In my search I found a source offering brand new injector pumps at the normal rebuild cost plus free shipping [To Alaska that is a item as many lower 48 states consider us a foreign land!!]
I purchased this pump. The arrival was four days from the East coast and the mechanic installed. Now here is the interesting discovery.
On start up all was well 550 RPM out of the box. Following warm up the maximum throttle RPM in neutral was 1900 RPM. The old pump allowed near 2800 RPM in neutral. It has been believed that was the accepted normal WOT RPM even knowing that in some applications the engine is rated at 3000 RPM WOT. I had never given the thought to the difference and how that was obtained.
As we pondered this shortage of RPM at WOT, the mechanic adjusted the full throttle setting to the max. We obtained 2500 RPM with his forcing the pump to the furthers point. Still thinking on it, the mechanic then had a ‘Eureka’ moment. He sought out the replaced pump and read the plate on that pump. It ended with the numbers “2750” He read the numbers on the replacement pump which were “2200”.
As I do not exceed 1600 RPM while in operation as that is ‘Hull Speed’ max. I normally set the throttle between 1450-1550 RPM. With this setting the pump delivery is still far more than the demand will ever be.
The point of this post is in discussion of over propping always includes the ‘'”Recommended wheel based on the manufactures RPM rating” So in the case of our engine as applied to marine use, the two RPM ratings, 2800 and 3000 are in play depending. The assumption being in any discussion is that the engine in question is achieving that RPM, There is not a proviso “If”. Here now is a “If” situation. Were I to sell the boat the new owner not being able to achieve 2800 RPM would inquire to a source such as this forum and receive multiple responses as to why he is not able to obtain WOT setting of 2800. The more probably response would relate to “Over Propped”.
In this case it may be a factor, however that the fuel injector pump is ‘Rated at 2200 RPM’ if that is the case with the relationship of these numbers given, then the engine will not exceed for lack of fuel, RPM over the 2200.
I am submitting this to the forum for digestion and comments. As everything related to this pump and our boat operation reflecting a smooth operation, it would not be an intention to make any changes, yet it would not be unheard of to have other or future readers come in contact with a similar or same issue.
Regards,
Al-Ketchikan
Within the last couple of days an interesting issue regarding the discussion of ‘Over Propping’, WOT, and such became relevant.
The subject has several threads in history, yet this I believe, is a different approach to the subject as a whole with a specific point.
A couple of weeks ago while diagnosing a different issue, [Why did the tachometer not register with the engine running] for a future subject, the young mechanic noticed that my fuel injector pump housing was damp with leaking fuel. Not bad or dangerous, but noticeable. I then stated that within the last couple of outings, the throttle idle had dropped from the normal 550 down to 200 or less. Everything ran well, there was not concern with the range of throttle while underway, that the idle had dropped without any adjustment was nagging.
The mechanic indicated that there were springs within the pump and that the drop without any physical involvement happened and the pump was showing leakage perhaps a re-build of the pump was in order.
With the time frames involved with removing, shipping, re-building, shipping back and reinstalling, I decided to search out a rebuilt pump or new depending on cost. In my search I found a source offering brand new injector pumps at the normal rebuild cost plus free shipping [To Alaska that is a item as many lower 48 states consider us a foreign land!!]
I purchased this pump. The arrival was four days from the East coast and the mechanic installed. Now here is the interesting discovery.
On start up all was well 550 RPM out of the box. Following warm up the maximum throttle RPM in neutral was 1900 RPM. The old pump allowed near 2800 RPM in neutral. It has been believed that was the accepted normal WOT RPM even knowing that in some applications the engine is rated at 3000 RPM WOT. I had never given the thought to the difference and how that was obtained.
As we pondered this shortage of RPM at WOT, the mechanic adjusted the full throttle setting to the max. We obtained 2500 RPM with his forcing the pump to the furthers point. Still thinking on it, the mechanic then had a ‘Eureka’ moment. He sought out the replaced pump and read the plate on that pump. It ended with the numbers “2750” He read the numbers on the replacement pump which were “2200”.
As I do not exceed 1600 RPM while in operation as that is ‘Hull Speed’ max. I normally set the throttle between 1450-1550 RPM. With this setting the pump delivery is still far more than the demand will ever be.
The point of this post is in discussion of over propping always includes the ‘'”Recommended wheel based on the manufactures RPM rating” So in the case of our engine as applied to marine use, the two RPM ratings, 2800 and 3000 are in play depending. The assumption being in any discussion is that the engine in question is achieving that RPM, There is not a proviso “If”. Here now is a “If” situation. Were I to sell the boat the new owner not being able to achieve 2800 RPM would inquire to a source such as this forum and receive multiple responses as to why he is not able to obtain WOT setting of 2800. The more probably response would relate to “Over Propped”.
In this case it may be a factor, however that the fuel injector pump is ‘Rated at 2200 RPM’ if that is the case with the relationship of these numbers given, then the engine will not exceed for lack of fuel, RPM over the 2200.
I am submitting this to the forum for digestion and comments. As everything related to this pump and our boat operation reflecting a smooth operation, it would not be an intention to make any changes, yet it would not be unheard of to have other or future readers come in contact with a similar or same issue.
Regards,
Al-Ketchikan