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Re: Timing belt - engine breakdown??

posted by  someone claiming to be M.Aaro on  Thu Aug 20 23:30 CST 1998 [RELATED]

ICQ>

All the oem heads have a combustionchamber height of 12mm, nominally.

The gasket has a compressed thickness of 1.25mm, nominally.

The valvehead side has a height of 1.25mm, nominally.

The piston at tdc is below deck with 0.2mm (a lot of different measurement here! No one although is above deck at tdc.)

If the valveseats on the valves are at the outer edge of the valves (normally not in oemcut valveseat on oemheads) the following valve is safe:

12mm + 1.25mm + 0.2mm -1.25mm => roughly 11.8mm max valve lift STATICALLY...

DYNAMICALLY: At a high rpm (maybe like a missed gearchange...) the "stretch" of the rod and piston assembly takes/stretches roughly 1/10mm for each 1000rpm i.e. "a new rpm record" of 7000rpm reduces the 11.8 figure down to roughly 11.1mm of a "safe valvelift" IF/WHEN the cambelt is lost...

(The Heron/B230K has no combustioncamber in head.)

See list further down of critical oem valvelifts.

I suggest; change the cambelt at recommended intervalls!

The Volvo sohc is a very safe engine!

Stay away of uninformed mechanics and find one with the neccessary know-how...

If you anyhow want to break the cambelt; never change the belt and run without a cambelt cover on dirt roads, preferably with the underlying enginecover removed...

BR

M.Aaro

List of oem net valvelifts above 11mm:

D/11.2mm

V and consequntly VX/11.37mm

K/11.95mm

H/12 and 11.5





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