BMC Knocking

[Liam webb]

hi there got a BMC 1.8 it seems fine in tickover hardley any smoke, put it in gear it starts knocking also starts to run hot after about 30 to 45 mins. could this be either head gasket, or big end bearing gone.

many thanks

Liam

[Tony Brooks]

More information required. It could be a gearbox fault, broken engine mount or foot, especially if the stern gland is smoking after 30 to 45 minutes. I would not expect a big end to cause overheating in its initial stage of failure but a head gasket might but I would not expect that to normally cause knocking. maybe two faults?

 

Ideal we need some history, info about coolant use, and a sound file or video of the engine when the noise occurs.

[Tony Dunkley]

hi there got a BMC 1.8 it seems fine in tickover hardley any smoke, put it in gear it starts knocking also starts to run hot after about 30 to 45 mins. could this be either head gasket, or big end bearing gone.

many thanks

Liam

 

Not having much luck with engines in boats are you ? . . . just over 3 weeks ago you posted the following about a Lister ST2 : ~

 

Posted 28 August 2016 06:19 PM

 

"Right, iv set the gov up on my lister st 2, but its still ticking over way to quick when you go to turn engine off the rack is almost fully back as well I mean its mm. But if you open it up and control it on gov by hand it ticks over lovley this is with the morse disconected. You then stop engine and re start and back to square one again. Any ideas and sometimes has a habbit of running away too. Both pump marks are spot on with the sides of the housing so im baffled know.could retarding fuel pump timing move the rack to a diffrent position "

Edited September 19, 2016 by Tony Dunkley

[Tony Brooks]

I see Liam lists his occupation as mechanic. I just hope he is not charging for services to boaters and coming on here to get us to make up for gaps in his knowledge and experience. That sort of behaviour winds me up a treat. However if he is simply trying to help fellow boaters without any thought of payment I am happy to help if I can.

 

How many can remember the chap who announced that he was offering "a quality service" to boaters and within days proved he had no idea that an LH150 gearbox needed the engine running before it would put itself into neutral.

[Tony Dunkley]

 

I see Liam lists his occupation as mechanic. I just hope he is not charging for services to boaters and coming on here to get us to make up for gaps in his knowledge and experience. That sort of behaviour winds me up a treat. However if he is simply trying to help fellow boaters without any thought of payment I am happy to help if I can.

 

How many can remember the chap who announced that he was offering "a quality service" to boaters and within days proved he had no idea that an LH150 gearbox needed the engine running before it would put itself into neutral.

 

 

I believe the term "mechanic" is Americanism for contract killers, . . . . but I don't know if there's an equivalent for people who bugger up engines.

[Iain_S]

Are you sure the knocking is coming from inside the engine?

 

Once when we picked up Copperkins, a shared boat, the engine sounded like a bag of nails. Cause was one slack engine mount, and two broken mounting legs.

 

I can envisage a situation where a similar fault could increase the load on the engine when in gear, which could lead to overheating, if he cooling system was a bit marginal.

[Tony Brooks]

as per post 2. Check simple things first.

[Geoff Taylor]

Broken mounts etc may make a noise etc but will not cause overheating, a big end problem would show itself pretty quick by a drop in oil pressure and rise in water temp and total engine failure would soon follow.

 

Maybe a faulty thermostat on the cooling side assuming knocks are mountings and oil pressure ok , it was not mentioned if the engine is raw cooled or skin tank so a problem could be there. The head gasket can be checked with a chemical test kit and the knocks could be lurking in the injection system caused by a faulty fuel injector (a "crack" test will eliminate this).

 

The art of diagnosis is the order in which it is done, I tend to check the easiest first and do not jump to conclusions and keep calm !!.

[Liam webb]

Just to clarify things, the st2 is in my own boat, and was very badly maintained so iv gone through and rebuilt it, the posts I have put up on here have been to help me fault find on a few things that were wrong with it, from when the fuel pumps had been set up after being reconditioned.

I have been doing mechanics for rather a long time know, and I always like to hear other peoples opnions on what the problem might be, as evrey one is diffrent and diffrent sujestions, after having alook at the bmc, it appears to have bent an exhuast valve. As it is slightly off set to the rocker arm, and also has alot of gunk in the rocker box exactly where this one has bent, problem diagnosis, so then problem will be fixed.

Liam

As o have also stated above I just do mechanics as a hobby and to help people out. As I have all the tools and kit. But I akways like to hear other peoples thoughts on what things might bee. Evrey day is a learning curve with stuff, and evrey problem can show many diffrent signs

[RLWP]

hi there got a BMC 1.8 it seems fine in tickover hardley any smoke, put it in gear it starts knocking also starts to run hot after about 30 to 45 mins. could this be either head gasket, or big end bearing gone.

many thanks

Liam

Doesn't sound like a bent valve to me

 

Richard

[Tony Dunkley]

..... ...... ............ ........ after having alook at the bmc, it appears to have bent an exhuast valve. As it is slightly off set to the rocker arm, and also has alot of gunk in the rocker box exactly where this one has bent, problem diagnosis, so then problem will be fixed.

 

 

Firstly, any engine with a bent valve isn't going to run alright at idling, or at any other rpm's. Secondly, valves don't bend at the rocker end of the stems, . . . they bend at the other end of the stem, below where it protrudes from the guide into the port.

 

If the top end of the valve stem isn't sitting directly under the rocker pad, and there's a lot of carbon and soot around it, then the guide, and probably the valve stem, are either very severely worn or the guide itself has worked loose in the head. Whatever the problem with the valve and guide turns out to be, that won't be the cause of the overheating after running for half to three-quarters of an hour, so you need to look elsewhere for the cause of that.

[Liam webb]

I think iv already found that problem as well the water pumps on bmc engines are known for trouble this one appears to be leaking and has a good wobble on it. Where the fan belt goes arround it

Liam

[RLWP]

 

Firstly, any engine with a bent valve isn't going to run alright at idling, or at any other rpm's. Secondly, valves don't bend at the rocker end of the stems, . . . they bend at the other end of the stem, below where it protrudes from the guide into the port.

 

If the top end of the valve stem isn't sitting directly under the rocker pad, and there's a lot of carbon and soot around it, then the guide, and probably the valve stem, are either very severely worn or the guide itself has worked loose in the head. Whatever the problem with the valve and guide turns out to be, that won't be the cause of the overheating after running for half to three-quarters of an hour, so you need to look elsewhere for the cause of that.

 

 

The easiest valve problem I ever diagnosed was on a Triumph Herald. Removing the rocker cover, there was the end of the valve poking up above the rocker shaft. The end of the rocker was broken off and sitting in the oil next to the spring

 

Goodness knows where the valve head was, or what it had done to the piston

 

Richard

[Liam webb]

Problem solved. Worn valve guide.

[Geoff Taylor]

No way would the valve guide cure the problems with this engine, what you have probably done is inadvertently solved it by replacing the head gasket that was possibly starting to blow, I have seen engines running quite well with all of the guides knackered and the only tell tale sign is being that of blue smoke and using oil.

[Mikexx]

No way would the valve guide cure the problems with this engine, what you have probably done is inadvertently solved it by replacing the head gasket that was possibly starting to blow, I have seen engines running quite well with all of the guides knackered and the only tell tale sign is being that of blue smoke and using oil.

 

I also find it difficult to believe a worn valve guide would cause a knock and overheating. The only symptom I would expect is perhaps excessive oil consumption.

 

I believe your diagnosis is more likely.