Interferance or non interferance

volvoken , It is extremely rare but can happen , it depends on the engine speed and at which point the belt decides to say bye-bye , I have yet to to see one do it. Mister T.

I have often read this discussion about the B200F engine, so recently when I was changing the timing belt I did an experiment. Carefully turning the crankshaft by hand when the belt was off proved that there was definitely interference. It was not an exhaustive check, ie I did not try keep trying with different camshaft positions to see whether there might randomly be a non-interference position, I just tried the position the engine had naturally stopped at. But I would have thought that there was bound always to be at least one valve open one cylinder, so even if the camshaft stopped dead when the belt broke, the crank would go on turning so the piston was bound to reach TDC and hit that valve. That's in a 1993 Torslanda. I always understood that these had to be interference because they had higher compression ratios to compensate for squeezing the capacity below 2 litres. Earlier cars did not have this restriction, so were mostly non-interference, hence the often-repeated statement that most Volvos were non-interference.

generaly the pre 1984 engines ( B21A , E etc ) are ok but later black top engines are not ...

I was under the impression that all B21/B23 engines were non-interference, whereas B230/B200 units were interference ones. I think that the combustion chamber design on the B200/B230 units, which is referred to as "Heron Head", accounts for the loss of a very useful mechanical safety feature. I'm not so sure about the Compression Ratio per se being the culprit: the Turbo units run a relatively low CR, but are still interference types. Perhaps a cylinder head guru can enlighten us? (Alas Bill Blydenstein is no longer among us.)

The Heron Head is rare and Only used on the B230KH ( H for Heron) unfortunatly the H is ommited from the designation printed on the cam cover on some engines ! But they have EGR and pulsair which helps in indentification ...

ive seen b230 engines , bend a couple , it does depend on some things as posted above , however some HC versions of the B200 are definitely interference . that said , it was only one instance of a B230 .