Repowering with Perkins 4.108 -- Have some questions...

[sww914]

There is no way that I will ever use synthetic in an old design engine that hasn't been broken in. Never again. I had 2 that the rings never seated because the synth lubricated too well and I had to tear them down and re-hone the cylinders and replace the rings. Once it's broken in, great, in an engine designed for synth, great, but never on an old design.

[Astral Blue]

Originally Posted by sww914

There is no way that I will ever use synthetic in an old design engine that hasn't been broken in. Never again. I had 2 that the rings never seated because the synth lubricated too well and I had to tear them down and re-hone the cylinders and replace the rings. Once it's broken in, great, in an engine designed for synth, great, but never on an old design.

Thanks for the insight! I never considered the lubricating strength of synthetic oils to play a role in preventing the rings from being seated...but what you mentioned makes perfect sense! I'll keep that in mind. For the break-in period, it's non-synthetic!

[djmarchand]

Synthetic oils have two advantages over petro oils: they lubricate better and they don't break down (oxidise generally) over time so that you can run longer between oil changes.

But with diesels, particularly old NA diesels you still have to change the oil to remove the soot loading. If you don't the oil loses lubricating capability.

So one of the advantages of synthetics is out the window and the other just isn't worth it IMO. Modern petro oils have more lubrication capability than oils available when your Perkins was designed.

David

[capttman]

I would love to find a surplus 4 108. Know of any in the states?

[Cheechako]

Did this project ever get completed...?

[Astral Blue]

Originally Posted by Cheechako

Did this project ever get completed...?

Yes, our first sea trial was on Sunday. Here are the results:

We took her out for the first time on Sunday, since fixing the tachometer. She performed beautifully!

The information here is limited -- as I need to repitch my propeller and am experiencing problems with the FloScan meter. I will continue to update this section as I gather more data.

Here are a few observations:

Sound:

The Perkins 4.108 is much louder at idle than it is at say 1500 RPM's. As the RPM's increase, the clunking noise common to Diesel engines smooths out and becomes hardly apparent. The waterlock muffler is definitely the way to go with respect to suppressing the sound coming from the exhaust. There is a huge difference compared to when the engine was operated without it.

The fact that the cabin and helm are well isolated from the engine compartment helps tremendously. And when the door to the cabin is closed, it is hardly bothersome.

Exhaust smoke and smell:

On a cold start, there is a considerable amount of exhaust that appears for the first 30 seconds. This is non-existent during warm starts.

As the engine warms up, the exhaust subsides and becomes a non-issue.

Speed:

She was able to hit 8 knots, but it was at very high (3400) RPM's. The propeller's pitch is too low. There is a considerable amount of cavitation and the engine is attaining high RPM's effortlessly. I'm currently using a 16X9 propeller. I want to get some base line data before proceeding with repitching it. I ordered a 15X15 propeller to use as a diagnostic tool. Once I am able to gather data from a propeller with an extremely high pitch (for this hull and engine), I will have baseline measurements and can accordingly repitch the original propeller more accurately. I had an extensive conversation with Steve from Thomas Marine Propellers, and he concurred with this strategy.

Fuel Usage:

No data to report yet. I am having a problem with the return sender on the FloScan unit. Will report fuel usage data when the problem is corrected.

Engine Temperature:

160 degrees F is maintained at idle and lower RPM's. The temperature jumps to 170 degrees F at 2200+ RPM's. This is consistent with the manufacturer's spec sheet.

Oil Pressure:

50 PSI at starting, gradually dropping to 40 PSI upon engine warm up. There is very little difference in oil pressure at varying RPM's. This is common to the Perkins 4.108 engine.

[Cheechako]

Cool... thanks!... keep us posted. I think you'll find fuel usage so low as to not worry about....

[phorvati]

Interesting stuff Astra Blue. I have 15/9 prop and was not reaching hull speed. I was not going pass 2400rpms tho. Definitely noticing the slip as i motor into wind, for instance going into 25-30kts calm water, speed does not get over 3kts. I am curious to see what you get with 15/15. I am looking for something in the order of 15/12 for next year.

[Cheechako]

Phorvati, what is your max rpm wide open?

[Astral Blue]

I put together a photo album of the project, from beginning to end. Here is the link:

http://flic.kr/s/aHsjCycscX

[Astral Blue]

Originally Posted by phorvati

Interesting stuff Astra Blue. I have 15/9 prop and was not reaching hull speed. I was not going pass 2400rpms tho. Definitely noticing the slip as i motor into wind, for instance going into 25-30kts calm water, speed does not get over 3kts. I am curious to see what you get with 15/15. I am looking for something in the order of 15/12 for next year.

What type of hull do you have? What is the length and displacement?

[DeepFrz]

Nice job Astral Blue. I hope the boat works well for you. By the way, where did you get the engine?

[Astral Blue]

Originally Posted by DeepFrz

Nice job Astral Blue. I hope the boat works well for you. By the way, where did you get the engine?

Thanks. I came across the engine on Craig's List.

[phorvati]

Originally Posted by Astral Blue

What type of hull do you have? What is the length and displacement?

C&C 38 its a fin keel 16k lbs displacement. Never really had it fully open, but I got to about 2400-2500 RPMs w/o increase in speed. I was still at around 5kts, nothing in tow, clean bottom.

[westwinds]

This is not a displacement hull so I think all the propeller calcuators are going to get it wrong. Will need some specific information for this hull like how much does it weigh with crew, passengers, provisions and 2/3 fuel. Put it on a trailer if you have one and take it and weigh it on a trucker's scale. Also need waterline beam, waterline length and hull draft. These numbers are used in the cavitation formula. What's the largest propeller you can fit on this boat with a tip clearance of 15% of propeller diameter? It's probably going to be small because a planing propeller is small making it difficult to get a propeller large enough to prevent cavitation; however, with four blades (or more?) and the right gearing it might be possible. What is the gearing, do you have a gearbox to reduce the propeller speed? What maximum RPM do you want to use since you will probably determine that from hull speed or will you need more than that if you want to tow, or have extra horsepower to buck wind. The cruise RPM is 3000, the maximum shaft horsepower is 42 at 4000.