Broken timing belt on startup

[DarrellK]

1978 Volvo Penta AQ120B. Ran yesterday for 45 minutes on lake. Ran great, started right up. At home, drained fresh water open system at manifold and heat exchanger. Also broke and drained lines to sea water pump. Closed system has antifreeze in it.

Temps were freezing last night and today.

Went to lake again today. Upon trying to start engine - ugly noise. Grinding like. I looked, saw nothing, tried again, same noise and then it quickly changed to a quieter almost spinning noise. Looked at engine again and found my timing belt was sheared. (Belt was in fine shape prior to this).

Was there water left in the bottom of the sea water pump that froze?
If so, is that enough to shear a perfectly conditioned timing belt?
Did I fry my impellor?

I figure I should start at the sea water pump, but not sure where to go from there.


Thanks for any input.

 

[jerryjerry05]

Re: Broken timing belt on startup

How old was the belt?
It's have to freeze pretty hard for the impeller to lock up.
Try turning the gear?
Try turning all the gears.
You have a manual?
Remove the pump cover and see what's in there?
Installing the belt can be a pain without diection.
Maybe look on U-tube for a video.

 

[DarrellK]

Re: Broken timing belt on startup

Thanks for the reply. We are currently under snow. When things warm up, I'm going to tear into it. Someone mentioned my cam may have been frozen to the belt. I'll let you know what I find out.

 

[cr2k]

Re: Broken timing belt on startup

The link below should get you all the info you need. Or at least to the right place to look for a 120.
I did one (pump rebuild, timing belt) last summer.
See if you can find all the seals before you start, I found kits on ebay for the cooling system seals.
This would be a good time to rebuild the waterpump (not just change the impeller) too, new shaft, seals and bushings come in a kit and can be done with garage tools.

Boatinfo - Volvo Penta AQ125A, B and AQ145A, B Engine Service Manual

Don't over complicate it, these were tractor engines before they made marine systems.
You may notice you only need a few sizes of wrench not 17 like the new stuff.

 

[user-name]

Re: Broken timing belt on startup

Tractor motor https://www.youtube.com/watch?v=iq9AY6uyaB8

 

[Walt T]

Re: Broken timing belt on startup

To shear the timing belt, something stopped the cam or intermediate shaft suddenly or one or the other was frozen up somehow. Seems pretty unusual to me. If it was original belt, well I suppose just the cold may have done something or it just decided to fail then. Once the belt has been removed make sure the cam, crank and intermediate shaft all turn nicely. I fear water may have gotten into a cylinder somehow and caused a sudden stop while cranking and sheared the old belt. Impeller easy enough to check but I don't think that's the cause.