Wot @ 3000 rpm?

[brewern]

As a newb boat owner, and an avid reader of iBoats, I checked my RPMs at WOT on our 'new to us' boat this weekend and it's topping out at just above 3000 RPM.

We have a 1980 Rinkerbuilt Runabout witha Mercruiser 3.0, 4 cyl. inline, 140 HP. The prop is 13.75", 21 pitch, and 15 spline.
If I'm understanding everything right, the RPMs seem low, as I should be between 4000-45000 RPMs.

Am I correct? If so, any suggestions on my next prop? Or, it 3000 RPMs proper for this boat?

Thanks!
Neil

 

[jimmbo]

Re: Wot @ 3000 rpm?

3000 is low. However, what tach was used and is it set properly for your engine? If accurate is the carb opening fully, is the spark advancing as the engine revs up? Is it firing on all cylinders? How is the compression?

 

[BonairII]

Re: Wot @ 3000 rpm?

It's time to check compression and spark.

Your probably missing on a cyl or two.

 

[Texasmark]

Re: Wot @ 3000 rpm?

21P for a 140 sounds like a lot of pitch, course it depends on the gear ratio. I just looked up data on 1997 stern drives. A 135 prop hp engine at 3 liter, 4 cyl, 2 bbl carb. runs 4400 to 4600 wot.
With the Alpha 1 outdrive it could have a 1.47 thru a 2.4 gearbox in the LU. I'm amazed but it could also have a Bravo 1, Bravo 2, Bravo 3, and a Blackhawk with ratios from 1.36 to 2.43. I cannot believe this inline 4, 140 hp engine could be equipped with all these outdrives......amazing.

Sooo before we could help you with a correct prop calculator, we need to know your gear ratio.

HTH,
Mark

 

[brewern]

Re: Wot @ 3000 rpm?

3000 is low. However, what tach was used and is it set properly for your engine? If accurate is the carb opening fully, is the spark advancing as the engine revs up? Is it firing on all cylinders? How is the compression?

The tach, as far as I know, is the original tach. It came with the boat, and looks like it matches the original decor. Outside of that, I'm not sure of any details.
The carb is opening fully and looks good. I've not done a compressions test on it, but besides some noisey valves, the engine is running great. Spark advancing? I'm not sure what that means. I assume you are asking abouot the distributor and timing?
It sounds just fine, so I'm quite sure all cylinders are firing.

Here's a couple of low quality videos of the engine running when I was diagnosing the valve adjustment problem:
http://www.youtube.com/watch?v=pK0MaB_xLog

http://www.youtube.com/watch?v=YwhXlna_5Wc

 

[QC]

Re: Wot @ 3000 rpm?

I have a hard time believing that boat planes as quickly as it does and also only reaches 3000 RPM. Check the tach before you do anything else!

 

[jimmbo]

Re: Wot @ 3000 rpm?

Something in the video is making a hell of a lot of noise. The boat looks like it gets up on plane without too much trouble. What kind of speed are you doing at wot?
Spark advancing.. as the engine runs faster the spark has to occur earlier in respect to TDC so combustion is completed in time for the piston to make best use of the expanding gases.

 

[jimmbo]

Re: Wot @ 3000 rpm?

I have a hard time believing that boat planes as quickly as it does and also only reaches 3000 RPM. Check the tach before you do anything else!

I saw an engine that had a badly worn camshaft it had good bottom end power but couldn't breath above 2000 rpm

 

[QC]

Re: Wot @ 3000 rpm?

Did you see his videos? And your example was in a boat? I am not saying it isn't possible, well I shouldn't have, but I always suspect a boat that planes well and also reports low WOT RPM.

 

[Maclin]

Re: Wot @ 3000 rpm?

In the first video, that sounded like more than 3000rpm to me....verify tach/rpm's as suggested first.

 

[Maclin]

Re: Wot @ 3000 rpm?

Did I miss the MPH at the 3000rpm posted somewhere?

 

[brewern]

Re: Wot @ 3000 rpm?

Something in the video is making a hell of a lot of noise. The boat looks like it gets up on plane without too much trouble. What kind of speed are you doing at wot?
Spark advancing.. as the engine runs faster the spark has to occur earlier in respect to TDC so combustion is completed in time for the piston to make best use of the expanding gases.

The noise is definitely the valves. I've adjusted them a couple times drydocked, and the noise seems to come right back. Next time out I'm going to adjust them with the valve covers removed and at WOT and see if I have better luck. If the crimped nuts are tightened down as expected, is there anything else that would make that valve chatter besides the nuts not being tightened down correctly? Am I hijacking my own thread?

jimmbo, replacing the gauges is on my winter to do list, so I guess that theory is on hold for a bit. Can I pick up a cheap gauge somewhere to check it next time we're out? Unfortunately, after looking at the calendar, it looks like we will only have 2-3 more trips to the lake before the cold hits. BOOOOOOOOOOOOOOOOO!

Thanks,
Neil

 

[jimmbo]

Re: Wot @ 3000 rpm?

Did you see his videos? And your example was in a boat? I am not saying it isn't possible, well I shouldn't have, but I always suspect a boat that planes well and also reports low WOT RPM.

As I said in a prior post "something in the video was making a hell of a lot of noise". The engine with the lopped off lobes was not in a boat, it was a 4.1 litre Cadillac engine, but it still had good low rpm torque for it's size, idled nice too. Just no cam lobes

 

[jimmbo]

Re: Wot @ 3000 rpm?

Don't mess with the valvetrain at wot, one it is too dangerous, hit a wave/wake and you could be tossed into the engine, two, you will have oil everywhere, three there is a risk of the valve not closing when adjusting lifters and could be hit by the piston. That is assuming the lifter'rocker arm are the adjustable type, most aren't, the nut is just tightened to a specific torque. Some Chevys were adjustable, one turn in from the zero lash point. While chevrolet had a process to set the rocker arm with the engine stopped, a lot of people will do it running, in 1/4 turn intervals to reduce the risk of the valve not closing.
The lifters might be stuck from varnish, a good detergent additive, GMs EOS is one of the best.
What kind of oil pressure does this engine have?

 

[jestor68]

Re: Wot @ 3000 rpm?

May I ask what procedure you used to "adjust" the valves, since you mention doing it more than once?

It should not be done(setting the lifter pre-load) with the engine running.

If in doubt as to the proper method of setting the pre-load on hydraulic lifters, you can find a couple of good videos on line. Just google "valve adjustment on Mercruiser 3.0L".

 

[steelespike]

Re: Wot @ 3000 rpm?

We need to first know what your gps speed was at 3000.
Also what was the load?
I suspect your tach isn't right.
To make up 1500 rpm you would have to go down 7" in pitch to something like a 14" prop.
A rediculess size for a runabout.
I hadn't read the lifter problem or seen the video though quick hole shot and low wot rpm don't usually go together.

 

[Texasmark]

Re: Wot @ 3000 rpm?

Adjusting valves? I had that engine when it was only 110 hp in a 1965 I/O. It had hydraulic valve lifters. The way you adjust a hydraulic valve lifter on a Chev engine is to get the rocker snug up against the top of the valve stem and then add 3/4 turn for preload. This puts a little pressure on the lifter and keeps it tight against the valve. It needs to be done with the valve closed....cam lobe 90 to 270 degrees away from the lifter. That way, when the lobe rises, the rocker is tight against the valve stem and the rising lobe compresses the valve spring, maintaining pressure, opening the valve and in the process no noise.

Prior to making the adjustment the lifters have to be filled with oil....on a rebuild. Yours should already be full of oil. Also it is done with the engine off.

Mark

 

[brewern]

Re: Wot @ 3000 rpm?

21P for a 140 sounds like a lot of pitch, course it depends on the gear ratio. I just looked up data on 1997 stern drives. A 135 prop hp engine at 3 liter, 4 cyl, 2 bbl carb. runs 4400 to 4600 wot.
With the Alpha 1 outdrive it could have a 1.47 thru a 2.4 gearbox in the LU. I'm amazed but it could also have a Bravo 1, Bravo 2, Bravo 3, and a Blackhawk with ratios from 1.36 to 2.43. I cannot believe this inline 4, 140 hp engine could be equipped with all these outdrives......amazing.

Sooo before we could help you with a correct prop calculator, we need to know your gear ratio.

HTH,
Mark

How can I find the current gear ratio? I looked at the lower unit and didn't see anything other than it's a Sterndrive and shows "SE106" on the side. I can also provide the serial # if that will help...

Did I miss the MPH at the 3000rpm posted somewhere?

I don't have a GPS, and the boat doesn't have a MPH gauge. I'll have a GPS before next season. Soooo, I'm not sure about MPH.

Don't mess with the valvetrain at wot, one it is too dangerous, hit a wave/wake and you could be tossed into the engine, two, you will have oil everywhere, three there is a risk of the valve not closing when adjusting lifters and could be hit by the piston. That is assuming the lifter'rocker arm are the adjustable type, most aren't, the nut is just tightened to a specific torque. Some Chevys were adjustable, one turn in from the zero lash point. While chevrolet had a process to set the rocker arm with the engine stopped, a lot of people will do it running, in 1/4 turn intervals to reduce the risk of the valve not closing.
The lifters might be stuck from varnish, a good detergent additive, GMs EOS is one of the best.
What kind of oil pressure does this engine have?

I probably should have noted the oil pressure gauge eh? On my next trip, I'll make sure I note the oil pressure. For now, would it be enough to run it with muffs and check the pressure that way?

May I ask what procedure you used to "adjust" the valves, since you mention doing it more than once?

It should not be done(setting the lifter pre-load) with the engine running.

If in doubt as to the proper method of setting the pre-load on hydraulic lifters, you can find a couple of good videos on line. Just google "valve adjustment on Mercruiser 3.0L".

I did find a video that showed exactly how to do it on this engine here:

Basically, I turned the engine until cylinder 1 was at top dead center on the compreession stroke. I adjusted the appropriate valves down to zero lash, and then 3/4ths of a turn after that. Then I got, I think it was cylinder 4 to top dead center, and adjusted the remaining ivalves the same way. It's all in the video, and the video agrees with my service manual.

We need to first know what your gps speed was at 3000.
Also what was the load?
I suspect your tach isn't right.
To make up 1500 rpm you would have to go down 7" in pitch to something like a 14" prop.
A rediculess size for a runabout.
I hadn't read the lifter problem or seen the video though quick hole shot and low wot rpm don't usually go together.

As mentioned, I don't have a GPS yet, but I'll definitely be getting one soon. Yeah, from 21 to 14 seems like a big jump.

Adjusting valves? I had that engine when it was only 110 hp in a 1965 I/O. It had hydraulic valve lifters. The way you adjust a hydraulic valve lifter on a Chev engine is to get the rocker snug up against the top of the valve stem and then add 3/4 turn for preload. This puts a little pressure on the lifter and keeps it tight against the valve. It needs to be done with the valve closed....cam lobe 90 to 270 degrees away from the lifter. That way, when the lobe rises, the rocker is tight against the valve stem and the rising lobe compresses the valve spring, maintaining pressure, opening the valve and in the process no noise.

Prior to making the adjustment the lifters have to be filled with oil....on a rebuild. Yours should already be full of oil. Also it is done with the engine off.

Mark

I thought maybe there is a problem with the lifters as well. I hope to remove the engine this winter and replace whatever I feel capable of replacing. See the video above for my method of adjusting the valves.

 

[brewern]

Re: Wot @ 3000 rpm?

Oh, and in case this helps diagnose the problem, the previous owner told me to use 5W30 for the oil. After mentioning that on iBoats, I found out I should be using 25W40, which I recently switched too, and changed the oil filter while I was at it.

 

[Texasmark]

Re: Wot @ 3000 rpm?

I thought maybe there is a problem with the lifters as well. I

If you have a bad cam lobe, and Chev engines had their share back then, you have a constant partially opening valve meaning that the required air for that cylinder will be reduced. if the lifter is adjusted properly for that bad lobe, there still will be no valve noise. Since an engine is an air machine, and only 4 cylinders, it could seriously affect performance if really worn.

A collapsing hydraulic lifter on the other hand, if leaking, can collapse under pressure. This does 2 things: It won't open the valve fully so you have the same problem as a rounded cam lobe but also, when the rocker turns it (the valve) loose, it (the lifter) may remain in the collapsed state for a half second which is enough time for the rocker to leave the valve then re contact it when it recovers and WALA you have a tick.

I wouldn't expect all your lifters to collapse simultaneously. One or two maybe. So you should be able to go down the valve train with the cover removed and engine idling with something like the tube that paper towels are rolled on and find the ticker(s).

HTH,
Mark