ST2 bent pushrods- replacements required

[FadeToScarlet]

A neighbour's ST2 failed reasonably catastrophically with one cylinder completely stopping working and some horrible bangs; it turns out that one pushrod has bent, and the other bent and snapped.

 

What might cause this? That cylinder has always been a bit dodgy, I.e. Not running properly, so I suppose one might have been bent for some time, finally snapping and causing the other one to bend.

 

The main thing is, I think, to eliminate and check things before replacing the push rods.

[Jay4424]

timing gears/pushrod shaft/valves/springs/clearence between piston and valves (debris)/any and all keyways

 

 

just as a starter for 10!

[BEngo]

Possibly sticking valves or rockers which have refused to go down and then the push rod has bent. Check that the valve stems are clear of carbon, the rockers are free and the valve gear oil feed is working.

 

I would also have the head off to check that the cylinder/piston is OK- a stuck valve may well have been hit by the piston.

 

 

N

[Bee]

Ooo that needs looking at, I would like to remove the head really just to make sure that its all ok and valve stems are not bent, a couple of pushrods are not a big problem but all the other moving bits need a careful looking over - and rockers and shaft etc.

[zenataomm]

I once knew someone who had re-assembled an air cooled cylinder head by tightening the rocker arm back down on to the head without slackening the tappets off first. The push rods took all the strain.

Why am I telling you this? About a month later an impressive sound effect pointed to one snapped push rod and another one kinked.

 

Alternatively ....

Exhaust valve has gathered clinker around the stem and stuck in the open position.

Push rod has dropped off the tappet when the cam dropped and then come back up whilst detached at the top.

Edited May 16, 2015 by zenataomm

[FadeToScarlet]

Right, looks like that head to come off to check the piston and valves, crankcase door off to check the camshaft, and inspect the gears and timing marks before reassembly with new pushrods.

Oh, and give the engine a proper clean too it's filthy and sitting over a very soggy bilge.

[Arthur Brown]

IMO it'd the ideal opportunity to review a repair or replace decision, then perhaps to take the engine completely to pieces (on a bench?) and count the bits.

[FadeToScarlet]

IMO it'd the ideal opportunity to review a repair or replace decision, then perhaps to take the engine completely to pieces (on a bench?) and count the bits.

There isn't really the budget for a replacement, repair it has to be. I can at least check all the timings and the other pushrods, set up the tapper clearances, ensure the oil feeds to the rockers are properly connected, etc. and give all the parts such as the cooling fins a decent clean.

[RLWP]

Just do the heads for now. A timing slip on an ST would mean a major mechanical failure, which is rather unlikely

 

Richard

[FadeToScarlet]

Right, heads are off (thought I might as well take both off once all the cowling, manifolds etc. were off) and it's looking good.

 

The valves look completely fine on both cylinder heads, and the piston crowns don't show any marks at all. I think I might lap the valves and valve seats whilst the heads are off, to make sure they're free to travel, but other than that it's looking fine- unless there's a reason not to?

 

The pushrods in the other cylinder are dead straight.

 

The camshaft looks fine too.

 

Anyone know a source for new pushrods, now MES are AFAIK no longer trading?

[FadeToScarlet]

Edit to add- the only worrying thing was when I removed the exhaust manifold, a small amount of water came out. This is Not Good, obviously. There was none in the cylinder, but the exhaust pipe slopes downwards from the exhaust outlet to the engine, even though it's a long way above the waterline. In fact, thinking about it, the old silencer rotted through in places, which would be consistent with ingesting rainwater.

 

A job that needs doing is raising the pipe for a section before allowing it to drop to the engine, so stop any water ingress.

 

I'm at a loss though as to whether this is linked to the bent pushrods, or how, because the cylinder was absolutely bone dry inside.

[MoominPapa]

Edit to add- the only worrying thing was when I removed the exhaust manifold, a small amount of water came out. This is Not Good, obviously. There was none in the cylinder, but the exhaust pipe slopes downwards from the exhaust outlet to the engine, even though it's a long way above the waterline. In fact, thinking about it, the old silencer rotted through in places, which would be consistent with ingesting rainwater.

 

A job that needs doing is raising the pipe for a section before allowing it to drop to the engine, so stop any water ingress.

 

I'm at a loss though as to whether this is linked to the bent pushrods, or how, because the cylinder was absolutely bone dry inside.

Do the valves actually move? Water in exhaust manifold + engine sat for long period = valve rusted into guide causes bent pushrod.

 

MP.

[gazza]

Right, heads are off (thought I might as well take both off once all the cowling, manifolds etc. were off) and it's looking good.

 

The valves look completely fine on both cylinder heads, and the piston crowns don't show any marks at all. I think I might lap the valves and valve seats whilst the heads are off, to make sure they're free to travel, but other than that it's looking fine- unless there's a reason not to?

 

The pushrods in the other cylinder are dead straight.

 

The camshaft looks fine too.

 

Anyone know a source for new pushrods, now MES are AFAIK no longer trading?

 

Try these http://bryco.co.uk/

 

Used them in the past, they are in Daventry.

[FadeToScarlet]

Do the valves actually move? Water in exhaust manifold + engine sat for long period = valve rusted into guide causes bent pushrod.

 

MP.

Good point, I tried a bit yesterday but couldn't, will get it on the workmate and give a decent push. That would make sense for the chain of events you describe.

[FadeToScarlet]

Try these http://bryco.co.uk/

 

Used them in the past, they are in Daventry.

Brilliant, thanks.

[gazza]

Brilliant, thanks.

No Problem

[zenataomm]

Did the failure occur at start up?

I'm thinking water ingress = hydraulic lock = bent push rods.

[RLWP]

MES are most definitely still trading.

 

Richard

[David Mack]

MES are most definitely still trading.

 

Richard

 

And the list of surplus stock on the website includes

 

"Smaller Lister - LD/SL/SR/HSR/ST. Cylinders, heads, air ducting, camshafts, pushrods, housings,

flywheels & housings, governor parts, crankcases for SL1, 2 & 3, SR1,2 & 3, ST1 & 2, TS3."

[Thewatchmaker]

Did the failure occur at start up?

I'm thinking water ingress = hydraulic lock = bent push rods.

Bent conrod perhaps but how would both push-rods be under stress?

Edited May 22, 2015 by Thewatchmaker

[bizzard]

Even though you said that there is no evidence that the valves have struck a piston, and if the valves prove to not lap in properly lop-sidedly, therefore slightly bent I'd be inclined to remove the crankcase door to check the big end on that cylinder. As you said the engine has been running badly, noisely and probably on one cylinder for some time, so the valves striking the piston may have happened some time ago and oil, muck and carbon may have cushioned the blow leaving no evidence and the push-rod only just deciding to break.

 

Or and remove the cylinder barrel to check the piston small-end, con-rod for bentness, yanking the piston and rod up and down might reveal excess big-end play- wear.

Edited May 22, 2015 by bizzard

[FadeToScarlet]

Success! Installed the new pushrods from Marine Engine Services, lapped the valves, cleaned out the passages in the heads, had a general clean up to remove muck and carbon, replaced the heads, set the clearances on the valves, bled it through, and it fired up after a little bit of oil squirted into the air inlets.

 

One cylinder, it's clear, had been leaking past lots of shims into the cooling ductwork, leaving many years worth of un burnt carbon and fuel over everything, so I cleaned the fins as best I could, and all the engine pieces, and will run it off load without all the shrouding for a bit to check for any other leaks, but having cleaned up the mating faces and torqued the head nuts on properly (they undid pretty easily with a spanner before!) I hopefully won't have to.

 

It runs much more smoothly now, on both cylinders, without as much hunting and rev changing, which it used to do.

Edited June 18, 2015 by FadeToScarlet

[Tony Brooks]

Sorry to come late to this thread but a question that may help.

 

Is the ST one of the models that use either aluminium tube or normal steel push rods? If the answer is yes then maybe the aluminium rod valve clearances\were set to the steel setting or the valve clearances \were adjusted but with the settings transposed.