OK, explain this

I've got two 550 Secas, one with just under 8K and one with 22K miles.

On both bikes, the intake manifold rubbers are cracked to beat the band (not all the way through, but cracked.) Just like every other XJ in the world. ONE of them on the '81 could stand to be replaced.

So I'm looking at my "spare" head. I got a cylinder head off eBay a while back for $19.00; it came with its valve cover, cam chain tensioner and all the manifolds still on. It's grubby and dirty, just what you'd expect for $20 from eBay.

Except all four intake manifolds are PERFECT. PERFECT. Not a crack anywhere-- a bit grubby, but NO CRACKS. None.

WTF???

Wanna bet all the screws come right out too?

 

You might get lucky. I did. Thought I would change all the gaskets on the inlet manifolds, and all the Allen bolts came right undone. They now have anti-sieze on them too. The exhaust header bolts came off easily too. Sometimes you get a win. The manifolds on my XJ are fine - no cracks.

 

Fitz, the crubbiness can actually be a good thing. UV rays if I understand things correctly is the biggest enemy of rubber. I bet your your spare head was also kept in a garage somewhere - away from direct sunlight?

 

I keep reading about cracked intake boots
But "up here' I've not seen ..Any... with that problem. I suppose UV and chemical laden air plays a large part.
Brings a disturbing thought to mind though.. IF.. the above does such damage to Rubber bits imagine what it;s doing to YOU Time to Move??

 

I think its the storage and sun like mentioned Fitz. My 650 manifolds are great as are the XS400 manifolds, although the 400s air boots are like rocks - no cracks though.

 

I would think hot and cold cycles would be the killer of manifold boots.

 

The flexing from the intake pulses and then a few carb back flashes you got a lot of stress on the rubbers. Next time youy light it off just put your fingers on the side of them and you willl feel them pulsing and carrying on. The gas going thru it also isn't all that friendly to rubber either.

Art

 

could simply be the the PO replaced them!

 

Yep. Also, ozone is hard on rubber. If the thing's been stored in a dark corner of a damp basement for 20 years the rubber won't age nearly as much.

 

[quote="MiCarl ... If the thing's been stored in a dark corner of a damp basement for 20 years the rubber won't age nearly as much.[/quote]

True, but the engine will be crap ... <grin>

 

My intake and manifold rubbers look new too, both sets, 16 total. the ones that are on the girl now and the ones on the spare. guess I got lucky too