utskicat
Seaman Apprentice
- Joined
- Dec 15, 2015
- Messages
- 41
The History:
Original setup was 1975 Mercruiser 888 with Ford 302. 888 outdrive leg is good old MC-1. The old engine was high on hours and ready for rebuild or replacement. Boat ran smoothly before old 302 was removed. Sourced a low mileage early-seventies Ford 351W (automatic) from a Ford Galaxy 500 that had been tuned for a race setup but never really used. Seemed like a good upgrade since Mercruiser in 1975 also offered the "233" which was same outdrive but with the 351W engine. Same gear ratio as well.
The Symptoms:
Once the new engine was installed the engine hums away. Sounds and feels great. No vibration present at idle. When increasing speed and rpms, there is a vibration that is felt in the floor of the boat that did not exist with old engine. The vibration increases with throttle increase to WOT and is quite noticeable.
Important Details:
- 2 years before engine replacement stringers and transom were replaced and West Epoxy system was used so boat structure is fine.
- The only engine balance conversion performed was using the old 302 flywheel on the new engine since it had a flex-plate. A custom engine shop took the flex-plate and balanced the original 302 flywheel to match the balance of the flex-plate. So theoretically, the engine should be in balance. All 70's 302 and 351's used same 28oz flywheel. Not sure if the new engine had previously been re-balanced to an "internal balance", but if it had, the balancing performed by the mechanic should have addressed this.
- We are aware of the different firing order in the 351W from the 302. Firing order is correctly wired on new 351W.
- Outdrive has been reasonably serviced over the years. No obvious concerns of neglect here.
Unknowns:
- I do not know if trimming up or down or steering left to right affects vibration. Will test when the lakes melt.
- Do not know last time gimbal bearing was replaced.
- Have not pulled the drive yet.
Question:
I want to start troubleshooting this now while I have a lot of time on my hands. I am in Alberta, so our lakes are still frozen. I am looking for you guy's input on what the most important things to check first and in what order. At this point, they need to be things that do not require a lake test. I do have muffs though. I want to do a good service on the outdrive using a transom seal kit (bellows, gimbal bearing, etc). I also want to replace the shift assembly with the new redesigned kit and service the water pump impeller and seals. However, I don't want to pump much money into this 40 year old outdrive if its ultimately something major like gears. If that is the case, I'm guessing I'd be better off to look for a rebuilt Alpha drive?
So fire away at your thoughts on where to start and if there is something blatantly obvious about where this vibration could be coming from.
Original setup was 1975 Mercruiser 888 with Ford 302. 888 outdrive leg is good old MC-1. The old engine was high on hours and ready for rebuild or replacement. Boat ran smoothly before old 302 was removed. Sourced a low mileage early-seventies Ford 351W (automatic) from a Ford Galaxy 500 that had been tuned for a race setup but never really used. Seemed like a good upgrade since Mercruiser in 1975 also offered the "233" which was same outdrive but with the 351W engine. Same gear ratio as well.
The Symptoms:
Once the new engine was installed the engine hums away. Sounds and feels great. No vibration present at idle. When increasing speed and rpms, there is a vibration that is felt in the floor of the boat that did not exist with old engine. The vibration increases with throttle increase to WOT and is quite noticeable.
Important Details:
- 2 years before engine replacement stringers and transom were replaced and West Epoxy system was used so boat structure is fine.
- The only engine balance conversion performed was using the old 302 flywheel on the new engine since it had a flex-plate. A custom engine shop took the flex-plate and balanced the original 302 flywheel to match the balance of the flex-plate. So theoretically, the engine should be in balance. All 70's 302 and 351's used same 28oz flywheel. Not sure if the new engine had previously been re-balanced to an "internal balance", but if it had, the balancing performed by the mechanic should have addressed this.
- We are aware of the different firing order in the 351W from the 302. Firing order is correctly wired on new 351W.
- Outdrive has been reasonably serviced over the years. No obvious concerns of neglect here.
Unknowns:
- I do not know if trimming up or down or steering left to right affects vibration. Will test when the lakes melt.
- Do not know last time gimbal bearing was replaced.
- Have not pulled the drive yet.
Question:
I want to start troubleshooting this now while I have a lot of time on my hands. I am in Alberta, so our lakes are still frozen. I am looking for you guy's input on what the most important things to check first and in what order. At this point, they need to be things that do not require a lake test. I do have muffs though. I want to do a good service on the outdrive using a transom seal kit (bellows, gimbal bearing, etc). I also want to replace the shift assembly with the new redesigned kit and service the water pump impeller and seals. However, I don't want to pump much money into this 40 year old outdrive if its ultimately something major like gears. If that is the case, I'm guessing I'd be better off to look for a rebuilt Alpha drive?
So fire away at your thoughts on where to start and if there is something blatantly obvious about where this vibration could be coming from.
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