Engine won't do "flat out"

[magpie patrick]

Hi Guys:

 

I'm no engine expert: I can change the oil and the filters and know where to put the water in: I could change the fuel filters but bleeding the fuel system just aint my thing. I know a bit, but not much.

 

Following our crawl on the Ribble, I started thinking about overall performance: Ripple is no greyhound: steady, rather than fast, and overheats if left at full whack for too long: the deep draught, slightly blunt bow and engone/prop formation mean she will never set any records but...

 

Last summer she could belt along when she had to, wheras even before we got to the Ribble Link I has suspicions: not quite cutting it in reverse, struggling against a head wind... I think, neigh I'm al but certain, she's lost the top end. Day to day normal stuff fine, but when the going gets tough that last ounce of reserve, those last few revs that made all the difference just aren't there anymore. No, there's nothing on the prop and it is intact.

 

BMC 1.8, just had oil change and service, could perhaps do with an angine flush: surveyor thinks reconditioned when installed in 1999 (ex hire boat, new for 99 season, came off fleet after 6 seasons) others think probably brand new Indian or Turkish model. Smokes when cold and when under severe load. Has done as long as I've had her.

 

Any thoughts? What more information would help etc

[almostafloat]

try valve clearances if its breathing fresh air ok

[alan_fincher]

Has it always had an overheating tendency, or is it new/getting worse ?

 

Assuming it's cooled with a skin tank, how big is it, (i.e. how much area does it present to the hull side), and do you know if it's internally baffled ?

 

I believe someone in the know, (i.e. not me!), should easily be able to tell you if you have an old British built engine, or a more modern Turkish copy ?

(They are not identical).

 

Do you know the mariniser ? If it was Calcutt it will doubtless be on the engine, unless repainted, and probably the control panel to. For an engine supplied as recently as 1999, I think Calcutt, (if it were they), could tell you it's history. (Older ones they say they don't have easy access to the information).

 

Most BMCs smoke a bit when cold, and many when revved hard. It sort of comes with the territory, unfortunately.

[Keeping Up]

Throttle cable needs adjuxtment?

 

Fuel filter blocked?

 

Air filter blocked?

[Mick_B]

Throttle cable needs adjuxtment?

 

Fuel filter blocked?

 

Air filter blocked?

Stretched cable... Push the morse fully forward without starting the engine. Then check the lever on the injector pump to see if it has reached the stop. If you can move it a bit more try adjusting the cable.

 

If the fuel filter is blocked you would normally hear the engine starving, trying to go a bit faster.

 

A blocked air filter will always give you some nice telltale "excessive" BLACK smoke from the exhaust especially if you give it a good rev. However this could also point to worn injectors.

 

Excessive BLUE smoke when starting after sitting for long periods and then clearing after a minute or two would indicate worn valve seals as the oil seaps through when the engine is stopped.

 

If you rev the engine, knock it back to neutral until the rev's fall back and quickly rev it again, you may see a puff of BLUE smoke. This would indicate worn rings as the vacumn sucks the oil past the rings as the rev's fall. More noticible on road vehicles as the road wheels keep driving the engine during deceleration.

 

May be worth having a compressiion test done to see if there is excessive wear in the cylinders.

[RobinJ]

BMC 1.8, just had oil change and service, could perhaps do with an angine flush: surveyor thinks reconditioned when installed in 1999 (ex hire boat, new for 99 season, came off fleet after 6 seasons) others think probably brand new Indian or Turkish model. Smokes when cold and when under severe load. Has done as long as I've had her.

Sounds like its all interelated?

The engine needs to run to keep cool, load an engine and it will get hotter, anything that stops it running at its best will have the same effect, more load more heat!

When were the injectors last checked, is the fuel burning cleanly, is it sooted up? The injectors atomise the fuel when it is squirted into the engine, if a jet is blocked or sooted up, that piston will produce slightly less power, have larger carbon build up etc.

Have the valve clearances been looked at recently? When the valves open has a direct effect on the compression ratio and hence engine efficiency, over time the gaps will increase and the compression ratio goes down.

BMC's normally have a breather pipe, either from the oil filler cap or from the side of the tappet cover (under the exhaust manifold). It is worth cleaning these out (rinsing the steel gauze in solvent) and checking there are not blocked, but it will also gives some indication of the state of the engine. As an engine wears, more exhaust fumes are blown past the rings, at high revs when the crank is stirring up the oil, this can result in froth which gets blown through the breather pipe. Over a period of time this can build up in the air intake, be burnt in the engine and contribute to deposits in the exhaust. It may be that removing the exhaust manifold and cleaning the inlet and exhaust ports will help, but you can also think about what state the silence box is in, when was it last replaced? If you do replace it, think about running a brush (like a chimney sweep) throught the rest of the exhaust.

How worn are you fan belts? A new fan belt may not improve things by a lagre amount, but worn belts can also affect engine load, as they wear they sink into the pulley deeper and place a slightly larger load on the engine.

All this will help your engine to breathe and run at peak efficiency and is worth doing before you think about a major overhaul.

[gary4lw]

Have you filled the boat up with stuff ?????

[John Orentas]

I still have an idea that something is impeding the boat from going through the water, I know your first thought was to check the prop for fouling but check it again, some funny things can happen.. Hooking up a tarpaulin under water could do it, so could two or three extra passengers or equivalent 'stuff' as Gary suggests.

 

Engine over heating or becoming greatly out of tune will normally give other clues, most have been mentioned but watch and listen for things unusual.

Edited April 28, 2008 by John Orentas

[Peter Reed]

You can download BMC owner and workshop manuals from www.calcuttboats.com

[Timleech]

I still have an idea that something is impeding the boat from going through the water, I know your first thought was to check the prop for fouling but check it again, some funny things can happen.. Hooking up a tarpaulin under water could do it, so could two or three extra passengers or equivalent 'stuff' as Gary suggests.

 

Engine over heating or becoming greatly out of tune will normally give other clues, most have been mentioned but watch and listen for things unusual.

 

When was the boat last docked? is it moved regularly?

Weed growth etc can cause similar symptoms, especially if the engine is already fully loaded by the prop.

 

Tim

[magpie patrick]

Hi Guys, lots of useful ideas, some of which are beyond me to deal with but I'll start with those I can when we are next on the boat in a couple of weeks time.

 

Jon and Tim: I hadn't thought of a tarp being caught: on the Ribble (where she really struggled) current and headwind were supplemented by having six passengers and, as per BW advice, a full tank of water. However it was on the Bridgewater I was having suspicions as I couldn't get Ripple to go too fast (why was I trying? I was already suspicious) as in flat out was only about 4 mph and no great wash: only the two of us on board and perhaps half a tank of water?

 

Boat hull was blacked in September 06 and has since done best part of 1000 miles: that said boat didn't move from November 4th until March 20th, Christmas cruise was cancelled due to bad weather.

 

Overheating: always has, as skin tank is a bit small for engine size at full revs: On the weaver last year I got an impressive fountain from the header tank. friends who didn't clear the prop went one better and got a jet of steam: so far this year the best I can get (if that's the right term) is the water just reaching the header tank vent which suggests the engine isn't getting as hot. As I haven't done anything to improve the cooling this isn't necessarily a good thing as it suggests it isn't working as hard.

 

So, when I get to Preston I'm going to

 

Check Prop and rest of hull for something caught

check vents, breather pipe and exhuast and clean out as necessary

check throttle cable

change drive belt (getting due anyway and I don't want it snapping on the return over the Ribble)

 

I'll probably change the oil again in lieu of a flush, but would an engine flush help?

 

valve clearances and seals is probably beyond me so I'll try the others first.

 

Thanks again: if anyone has further thoughts

 

Oh, and thanks for the manual links, I've been looking for one ever since I got the boat

 

what spendid people you all are

[almostafloat]

Sounds like its all interelated?

The engine needs to run to keep cool, load an engine and it will get hotter, anything that stops it running at its best will have the same effect, more load more heat!

When were the injectors last checked, is the fuel burning cleanly, is it sooted up? The injectors atomise the fuel when it is squirted into the engine, if a jet is blocked or sooted up, that piston will produce slightly less power, have larger carbon build up etc.

Have the valve clearances been looked at recently? When the valves open has a direct effect on the compression ratio and hence engine efficiency, over time the gaps will increase and the compression ratio goes down.

BMC's normally have a breather pipe, either from the oil filler cap or from the side of the tappet cover (under the exhaust manifold). It is worth cleaning these out (rinsing the steel gauze in solvent) and checking there are not blocked, but it will also gives some indication of the state of the engine. As an engine wears, more exhaust fumes are blown past the rings, at high revs when the crank is stirring up the oil, this can result in froth which gets blown through the breather pipe. Over a period of time this can build up in the air intake, be burnt in the engine and contribute to deposits in the exhaust. It may be that removing the exhaust manifold and cleaning the inlet and exhaust ports will help, but you can also think about what state the silence box is in, when was it last replaced? If you do replace it, think about running a brush (like a chimney sweep) throught the rest of the exhaust.

How worn are you fan belts? A new fan belt may not improve things by a lagre amount, but worn belts can also affect engine load, as they wear they sink into the pulley deeper and place a slightly larger load on the engine.

All this will help your engine to breathe and run at peak efficiency and is worth doing before you think about a major overhaul.

i think you mean the valve clearances decrease in time as the valves settle into their seats with the potential for lack of compression and a resultant loss of power see my first reply ,regards, stuart

[alan_fincher]

Do you have a temperature gauge, and what is the most it's going up to ?

 

Do you know what temperature your thermostat is designed to open at. (Typically this will be 74 degrees or 82 degrees).

 

Alan

[RobinJ]

i think you mean the valve clearances decrease in time as the valves settle into their seats with the potential for lack of compression and a resultant loss of power see my first reply ,regards, stuart

I appreciate that is possible, but my experience is that they increase over time, especially with build up of carbon on the seats.

When the valve clearances increase the valves open later and close earlier, thereby reducing the intake of air and expulsion of exhaust and reduce compression.

If they were to decrease the valves would open earlier and close later, thereby increasing the intake of air and expulsion of gases and increase compression.

[RLWP]

I appreciate that is possible, but my experience is that they increase over time, especially with build up of carbon on the seats.

 

That's interesting, what engine is this on? I know "A" series engines get increased valve clearances but that's because the tips of the rockers wear where they contact the valve head.

 

Richard

[almostafloat]

I appreciate that is possible, but my experience is that they increase over time, especially with build up of carbon on the seats.

When the valve clearances increase the valves open later and close earlier, thereby reducing the intake of air and expulsion of exhaust and reduce compression.

If they were to decrease the valves would open earlier and close later, thereby increasing the intake of air and expulsion of gases and increase compression.

ive never experienced increasing valve clearances through normal use and the inlet side is never exposed to pressurised gases even allowing for overlap in timing i must work on completely different engines but i would have thought that the ageing perkins 6354 4236 and leyland six cylinders that i constsantly maintain would be subject to the same principles as the bmc in question perhaps i,m wrong regards, stuart

[redfastlad]

Hi Guys:

 

I'm no engine expert: I can change the oil and the filters and know where to put the water in: I could change the fuel filters but bleeding the fuel system just aint my thing. I know a bit, but not much.

 

Following our crawl on the Ribble, I started thinking about overall performance: Ripple is no greyhound: steady, rather than fast, and overheats if left at full whack for too long: the deep draught, slightly blunt bow and engone/prop formation mean she will never set any records but...

 

Last summer she could belt along when she had to, wheras even before we got to the Ribble Link I has suspicions: not quite cutting it in reverse, struggling against a head wind... I think, neigh I'm al but certain, she's lost the top end. Day to day normal stuff fine, but when the going gets tough that last ounce of reserve, those last few revs that made all the difference just aren't there anymore. No, there's nothing on the prop and it is intact.

 

BMC 1.8, just had oil change and service, could perhaps do with an angine flush: surveyor thinks reconditioned when installed in 1999 (ex hire boat, new for 99 season, came off fleet after 6 seasons) others think probably brand new Indian or Turkish model. Smokes when cold and when under severe load. Has done as long as I've had her.

 

Any thoughts? What more information would help etc

Take the top off the lift pump poss 7/16"AF spanner or 10/11mm you will find a gauze filter in there which may be getting clogged up,if it is clear rebuild the pump and feel the lift pump mechanisim as they tend to get sloppy and the lift arm that runs on the cam will be worn to excess, so a new lift pump will be required this is my thoughts but its your engine!

[dave_2A_]

Had a similar thing on the way up from the K&A, which turned out to be the outer of the cable having pulled through the clamp a bit (probably due to spending 2 days flat out on the Thames) - 2 mins with a screwdriver and full revs were restored.

[Timleech]

ive never experienced increasing valve clearances through normal use and the inlet side is never exposed to pressurised gases even allowing for overlap in timing i must work on completely different engines but i would have thought that the ageing perkins 6354 4236 and leyland six cylinders that i constsantly maintain would be subject to the same principles as the bmc in question perhaps i,m wrong regards, stuart

 

My experience has generally been that valve clearances increase over time, but of course it's possible for them to decrease, it depends whether valve face & seat wear is greater or less than tappet, rocker etc wear.

Surely increased clearances will tend to increase the compression ratio? It may depend on the timing diagram for a particular design of engine, but it definitely can have that effect, and has in the past been used as a starting aid on some engines. It will certainly reduce gas flow and efficiency, though.

 

Tim

[Hairy-Neil]

Surely increased clearances will tend to increase the compression ratio?

 

Tim

 

I think you mean the compression pressure. Compression ratio is a fixed figure.....total volume divided by swept volume.

[Timleech]

I think you mean the compression pressure. Compression ratio is a fixed figure.....total volume divided by swept volume.

 

It'll affect the actual volume swept with valves closed, and therefore the actual compression 'ratio', though of course cannot alter the total swept volume.

I really don't mind how you refer to it, though

 

Tim

[Hairy-Neil]

It'll affect the actual volume swept with valves closed, and therefore the actual compression 'ratio', though of course cannot alter the total swept volume.

I really don't mind how you refer to it, though

 

Tim

 

Tim, I can't see that. The compression pressure cannot start to raise till the valves are fully closed, back to the fixed dimentions.

[Speedwell]

Patrick

My BMC 1.8 had a similar history to yours (I.e. Turkish ex hire) and had similar symptoms but worse. It turned out to be worn cam shaft lobes. Some of the valves were hardly opening at all, even though I had set the valve clearances correctly. I hope this is not your case but it is something to check if the simple things don't work.

Arthur

[Timleech]

Tim, I can't see that. The compression pressure cannot start to raise till the valves are fully closed, back to the fixed dimentions.

 

Take an extreme case where the valves only close with the piston halfway up the cylinder, crank at 90degrees. There's only half the available swept volume used for compression. If this is dependent on the inlet valve closing, it will be shutting as the piston rises on the compression stroke. Open up the tappet clearance, the valve won't open as far and it will also close sooner, ie when the piston is at a lower point in the cylinder, so more of the available swept volume is used, therefore more compression because the combustion chamber volume - the volume with piston at TDC - is fixed.

 

Tim

[John Orentas]

Hi Guys, lots of useful ideas, some of which are beyond me to deal with but I'll start with those I can when we are next on the boat in a couple of weeks time.

 

 

valve clearances and seals is probably beyond me so I'll try the others first.

 

Thanks again: if anyone has further thoughts

 

Oh, and thanks for the manual links, I've been looking for one ever since I got the boat

 

what spendid people you all are

 

 

Magpie.

 

Keep an eye on your skin tank though I doubt it it is the cause of your immediate problem, if an an engine has not boiled it's coolant it cannot really be overheating, the other way could conceivably do it though, it you check the thermostat it should be marked not much below 90 deg (raw water ones can be very low temp though), the coolant pipes should be 'very hot to the touch'.

 

We have had a few very interesting topics about under-size tanks, a few builders tend to cut corners with the sizes.