1GM 10. A question about revs.....

[vertford]

My little GM10 (2007)has a little quirk it seems. I usually run it for 10-15mins before we leave the buoy and then a bit more until we don't need it anyway. Not heavily used.

I noticed that this week when I went to full throttle on the return home that the engine rev noise changed and slackened off a bit and then perked back up again. There was no funny smoke out of the exhaust or major loss of speed. There is no rev counter.

Not being a mechanic of any type, is this a timing issue? I thought that maybe the pistons were sticking a bit because it wasn't fully warmed up yet, but what do I know! Injectors not spraying properly?

Oil level fine.

Thanks for any help.

 

[boguing]

Almost cetainly not timing. That can only get worse if the belt/chain slips, and will not get better.

More probable is a fuel/air problem. Blocked injectors don't generally get better either.

I'd start by looking at the inlet air path. No obstruction around the intake, then the air filter.

Next are the water and sediment filters in the fuel supply.

And then air leaks into the fuel supply.

Oh and a further thought - check for anything that might apply a force to the throttle cable. That would not be helpful.

 

[vertford]

Thanks. That sounds like a good check list to start with.

 

[Appledore]

More probable is a fuel/air problem. Blocked injectors don't generally get better either.

Had the same thing happen with my (much older) 1 gm 10 2 weeks ago. I had recently added thick sound proofing in the engine compartment, and I rather suspect I had made too good an air seal! After I opened up the engine cover I never had the problem re-occur.

 

[25931]

I found that "TinyTach" rev counters were well worth their (small) price.

 

[Old Troll]

1GM10

Prior to stopping the engine or whenever take an opportunity to give the engine a full or near full rev run on occassion. The engine will welcome the load and be much the better for it. Worthwhile fitting a rev counter.

 

[Tranona]

You are treating the engine in the worst possible way. They need to be run hard and always run long enough at good revs (over 2500) to get up to working temperature. The drop off in revs could be an air leak, but suspect the exhaust is coked up and could be the valves need reseating.

Before you do anything serious, take it out for a long run at full power, it should rev at 3400 minimum with no black smoke. Not easy to judge without a rev counter, but if the boat is propped correctly that should be maximum speed.

 

[maby]

When our 1GM10 behaved like that, I found the sedimenter half full of water and the O-ring on the fuel filler broken...

 

[Shearwater]

at fullest revs?

You are treating the engine in the worst possible way. They need to be run hard and always run long enough at good revs (over 2500) to get up to working temperature. The drop off in revs could be an air leak, but suspect the exhaust is coked up and could be the valves need reseating.

Before you do anything serious, take it out for a long run at full power, it should rev at 3400 minimum with no black smoke. Not easy to judge without a rev counter, but if the boat is propped correctly that should be maximum speed.

An idiot question perhaps, but you're saying it's OK to open the throttle to the fullest extent for some period of time? With no tach o or temp guage this would have to be guesswork. (I note earlier advice of Tiny Tacho and will get one)

 

[penfold]

Unless your propellor is very undersized it will not be possible to overrev with it in gear. Like Tranona says, engines are harmed more by underuse than overuse.

 

[prv]

The maximum ratings for the 2GM20 are 3600 (full throttle) for up to an hour, 3400 continuous. I'm not 100% certain, but I believe they're the same for the 1GM10.

In practice I don't go everywhere at max rated power, I cruise at 2800 which is 85% or so of max continuous. But the manufacturer is saying those speeds are OK.

Pete

 

[Old Troll]

Rev Counter

Cost of Yanmar Tachometer YN128170-91100 was £88,89p and Sender
YN1281170-91100 at £109.97p. Not cheap but for me since fitting the Rev counter has enabled me to have the satisfaction of getting 100% from the wee engine.

 

[Old Troll]

Rev Counter

Sorry got the cost wrong way round. Oh well back to the Bowmore.

 

[Burnham Bob]

a friend of mine was a car dealer and he used to do what he called 'an italian tune up' for cars that had pottered about on short runs. He would rev it as hard as he could through the gears and then bang it down the motorway. it blew away all the crud and it did seem to work. i always used to let my 1GM10 idle for a short while but never as long as 15 minutes before using it. try the run at full throttle and see what happens. running flat out for a while won't harm your engine.

 

[Tranona]

An idiot question perhaps, but you're saying it's OK to open the throttle to the fullest extent for some period of time? With no tach o or temp guage this would have to be guesswork. (I note earlier advice of Tiny Tacho and will get one)

Absolutely. All small high speed diesels operate in the range of 2000- 3600 (mostly). Yanmar recommend you run continuously at 75% max power, which on a 1GM is about 2800. It is governed to 3600 so you could never overrev it. If it is geared and propped correctly on the OPs boat it should hit max hull speed (5.5 aprox) at around 3400, but 3600 would be OK. crusie at 2800 would be just under 5, using about .75l hour.

Unlike most of the slightly more modern engines it is seawater cooled, so runs cool and needs to run hard for at least 30 minutes to get up to temperature. Should never be run without a working thermostat. Short, low speed runs results in coked up valves and exhaust and in extremes bore glazing. Run hard and often will last a lifetime with minimal maintenance. Mine has been running since 1992 in 3 different boats and runs as well as when it was new.

 

[Topcat47]

Another possible is that, if the exhaust is close to the waterline, at full power, the hull is being driven down at the stern, partially blocking the exhaust and upsetting the scavenging. This is the mechanism by which the gas flowing out of the cylnder helps draw in air into the cylinder on the downstroke. I sometimes have this problem on Port Tack and we diagnosed the problem by having a crewmember move from the cockpit to the pulpit while motorsailing.