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Sucking sound from bmc 1.5 air intake


boode

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So we've recently had the head gasket replaced and all was fine but now engine won't start and we have a loud sucking noise every 4th stroke coming from the air intake when we try to start....any ideas?

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Have you checked the valve clearances? That sucking sound might be a blowing sound.

 

I would want to do a  compression test because I fear it may be a gasket failure between two cylinders, especially 2 & 3. This would be more likely if the head and block were not checked for flatness before replacing the gasket OR some half baked method was used for tightening the cylinder head gasket if the mechanic did not have a crows foot spanner.

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You say ''all was fine a first'' Mmm, I think I'd be checking the timing chain as well it may have snapped or jumped teeth if the tensioner is in trouble. Can you hear definite regular gur, gur, gur, gur of each compression as you turn it over on the starter?

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On 11/03/2020 at 13:02, Tony Brooks said:

Have you checked the valve clearances? That sucking sound might be a blowing sound.

 

I would want to do a  compression test because I fear it may be a gasket failure between two cylinders, especially 2 & 3. This would be more likely if the head and block were not checked for flatness before replacing the gasket OR some half baked method was used for tightening the cylinder head gasket if the mechanic did not have a crows foot spanner.

Head and block both flat before replaced. valve clearance checked and tappets in correct cold clearance in accordance with the book. I didn't watch the guy replace the head so can't comment on crows foot. But I've ordered one myself and am going to redo work in the next week as im sending head off to replace all valves just incase.

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On 11/03/2020 at 13:08, bizzard said:

You say ''all was fine a first'' Mmm, I think I'd be checking the timing chain as well it may have snapped or jumped teeth if the tensioner is in trouble. Can you hear definite regular gur, gur, gur, gur of each compression as you turn it over on the starter?

When turned over you get the regular gur gur as you put it but as i said every 4th gur is a loud sucking sound. I will take the plate off and have a look at the timing chain today and see if anything is out of line....just getting annoying now as ive took this head off 3 times now and the engine is very close to being sledge hammered in my fits of rage. Had a day off to calm down.

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How was the truth of the block and head checked. Was it by straight edge and feeler gauges, abrasive paper and surface table, DTI?

 

There is no need to replace valve "just in case". When the head was off I would expect a competent mechanic to have ground them in, or at least had them out for a close inspection and checking their seating.  Only replace valve SEATS if they are cracked or burned,. To do so is to have an insert forced into the head and very occasionally they have been known to fall out. If it is a valve fault then once each valve is out the damaged seat is normally obvious.

 

also don't have new valve guides fitted unless you know they are worn.

4 minutes ago, boode said:

When turned over you get the regular gur gur as you put it but as i said every 4th gur is a loud sucking sound. I will take the plate off and have a look at the timing chain today and see if anything is out of line....just getting annoying now as ive took this head off 3 times now and the engine is very close to being sledge hammered in my fits of rage. Had a day off to calm down.

No plate t take off on a 1.5. Its the front pulley and timing cover. Might as well put an new timing cover oil seal in at the same time. When refitting put the pulley into the cover and then fit the whole thing. Put as many timing cover set screws in loosely as you can and only then start to tighten them. When tight take the pulley out to fit and you can't get at and torque up.

 

Don't hold the outer rim of the pulley to undo the pulley bolt. Jamb the flywheel.

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2 minutes ago, Tony Brooks said:

How was the truth of the block and head checked. Was it by straight edge and feeler gauges, abrasive paper and surface table, DTI?

 

There is no need to replace valve "just in case". When the head was off I would expect a competent mechanic to have ground them in, or at least had them out for a close inspection and checking their seating.  Only replace valve SEATS if they are cracked or burned,. To do so is to have an insert forced into the head and very occasionally they have been known to fall out. If it is a valve fault then once each valve is out the damaged seat is normally obvious.

 

also don't have new valve guides fitted unless you know they are worn.

Good to know, all valves look good and sit correctly, flatness was checked with some digital machine by mechanic as well as my own straight edge by myself as i removed head myself and had him replace it as i didn't have correct tools to replace.

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Just to be sure did you check the block. They can sink between cylinders. I don't think the 1.5 needs liner protrusion because it does not use liners so it should not be that unless it has been linered and one or more have sunk.

Edited by Tony Brooks
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9 minutes ago, Tony Brooks said:

How was the truth of the block and head checked. Was it by straight edge and feeler gauges, abrasive paper and surface table, DTI?

 

There is no need to replace valve "just in case". When the head was off I would expect a competent mechanic to have ground them in, or at least had them out for a close inspection and checking their seating.  Only replace valve SEATS if they are cracked or burned,. To do so is to have an insert forced into the head and very occasionally they have been known to fall out. If it is a valve fault then once each valve is out the damaged seat is normally obvious.

 

also don't have new valve guides fitted unless you know they are worn.

No plate t take off on a 1.5. Its the front pulley and timing cover. Might as well put an new timing cover oil seal in at the same time. When refitting put the pulley into the cover and then fit the whole thing. Put as many timing cover set screws in loosely as you can and only then start to tighten them. When tight take the pulley out to fit and you can't get at and torque up.

 

Don't hold the outer rim of the pulley to undo the pulley bolt. Jamb the flywheel.

Yes by plate i ment timing cover lol thanks for the advice :)

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Could you have ingested a foreign lump and bent an inlet valve head? if so you will have a big tappet gap on that rocker.   The injector heat shields top hats have been known to break up and drop bits into the cylinder.

 

Odd that it won't fire on 3 cylinders though....................................I would check everything else before tearing it down, you could reduce it to a box of bits and find out that it is something totally unconnected.

 

No smoke at all from the exhaust? Or even out of the inlet? if so its got no fuel. If the chain was far enough out of kilter to stop it I would expect lots of smoke from the inlet ports, hugely retarded.

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