Engine seems to start but rolls to a stop

[leecea]

the valve stuck open THEN got belted back up by the piston

I have a different engine (Yanmar 3GM) but I was curious if the typical small sailboat engines are interference designs?

[leecea]

Nevermind - a quick Google tells me that diesels are all interference engines.

Should have done that first

[skipperpete]

Originally Posted by leecea

I have a different engine (Yanmar 3GM) but I was curious if the typical small sailboat engines are interference designs?

Your 3GM has just enough clearance for the decompressors to work without damaging the valves. The Bukh is similar but it’s probable that his valve got stuck fully open because that’s where the engine stopped on the last shutdown, then possibly the moist atmosphere from the wet exhaust corroded that clean shiny valve stem. Sometimes they free up, other times not. The really bad interference collision is with the Volvo MD22 (Perkins Prima) when that timing belt breaks it’s pretty much all over as the valves get hit by the pistons, they don’t have the luxury of a pushrod to bend, just a solid camshaft so it ain’t good.

[JustinT]

Does anyone know of a good place UK postage to get Bukh gaskets? So far https://tnorrismarine.co.uk/ seems the only option.

[JustinT]

Just did the exhaust valve pushrod and with feeler gauge piston gap, Unfortunately on an experiential turn appears the valve is stuck downwards too, not just the stuck in the air arm.

[GrowleyMonster]

Originally Posted by JustinT

Just did the exhaust valve pushrod and with feeler gauge piston gap, Unfortunately on an experiential turn appears the valve is stuck downwards too, not just the stuck in the air arm.

I had assumed that this was the assumption.

In that case if you have not pulled the head, do so, and tear it down, take the whole assembly apart down to its individual components, polish, inspect, make sure oil can get into all the places it must get, and put it all back together. Be glad it is a two cyl and not six or eight. Everything is small and light and simple.

Get some nice trays for putting parts in. Take pics as you disassemble. Mark stuff, and lay it out in order. Don't be the guy who ends up with a big scrambled box of parts and no idea of how to put them all back the way that they were.

If you were to simply pull the head and take it to a shop, nobody would think ill of you, but it would probably cost you a couple hundred or a few hundred bucks to put it all to rights. Depending on how much work you want done.

[JustinT]

Ah, oh, thanks for the advice.

[Wotname]

You might be extremely lucky and find the valve spring is broken and that might be able to be replaced in situ but I strongly suggest you follow Growley's advice and remove the head. Take it home and find a comfortable place to strip in down. As Crowley suggests, your camera is your friend and have the service manual open at the same time.

Once you have done it once, you will be amazed how simple it is.

[deblen]

You will probably need a valve spring compresser tool.
Watch some Youtube vids of valve repairs.
Cheers/Len


Sample vid. Watch those flying keepers.

https://www.youtube.com/watch?v=qEe8C5u1LWg

[JustinT]

Thank you all.
I never thought of taking it home to the warm to fix it!

[JustinT]

Can't get the head off, am I missing something?
https://youtube.com/shorts/-UBBC3CTQOM?si=JzAxDlDWJBzFi69i

[Wotname]

Something is missing from the YT link, it isn't active!

There is nothing tricky about removing a DV20 head. Assuming you have followed the steps in C7 of the manual, it probably only needs a good whack with block of wood and hammer to loosen the 'grip' of the head gasket. Use some judgement though and don't go hammering it to death.

Other ideas include turning the engine over on the starter motor (with injector fuel pipe DISCONNECTED) hoping the compression on the good cylinder will aid in loosening the 'grip'.

When all else fails, a wedge (screwdriver blade etc) can be tapped into the joint between the head and the block to force them apart. Again judicious judgement is required not to do damage to the two surfaces.

Once the 'grip' is broken, the head will lift off without much effort.

[skipperpete]

I can’t get that link to open but if you get a couple of ordinary table knives, thin ones preferred and gently tap them into the gasket in a couple of places, the headgasket will either release or possibly split and the head will be freed. I use a couple of meat cleavers with very sharp edges and fine tapers, never use a screwdriver or any sort of thicker wedge and avoid going in further than an inch with the knife blade, often the liners protrude above the block deck and you don’t want to harm them in any way.
This advice assumes that you absolutely, positively dont have any remaining physical head to block connections such as a circulating pump, rocker shaft bolts , hidden unseen head bolts or lifting brackets

[Wotname]

Good point about the wedge has to be thin. I overlooked that essential piece of advice. Thanks for highlighting it skipperpete.

[skipperpete]

Haha, sorry Wottie , I was typing and having breakfast and never noticed your words of wisdom, it took me a long time to wake up to the knife blade trick, I started using cheap steak knives but finally settled on the meat cleavers….great for easing a gap on saildrive propshaft carriers to get em moving. For years, I used a big screwdriver and a selection of little ones but the turning point was when a workmate had trouble splitting off a Cat diesel head with screwdrivers and damaged the spacer….that cost him his job and us $1000 for a new spacer.
I’m embarrassed to confess to loosening off all the head bolts on a Perkins 6-354 and STARTING the engine as a last resort after wedges failed…. It worked but not nicely. Far better to do as you suggested with just compression.