Xu9 Main Bearing Cap Bolts / Studs

[Anthony 1,000]

Finally got around to picking up my 1.9 Mi16 (XU9J4) engine block amongst some other parts from the engine shop today, and spent a few moments staring at it because something didn't look right but I couldn't work out what initially. Ended up looking at some photos of previous engine builds and I worked out what looked odd - the usual arrangement of bearing cap bolts on mains #1, 2, 4, and 5 aren't bolts as you'd usually find, but instead are all a stud and nut affair like you'd normally find on main #3.

 

I've never personally seen this on an XU9 block, and looking at the pictures of few other XU9 builds that I found on here, none appear to have this arrangement. I'm assuming this has changed at some point in the past (I know the engine had been previously stripped and rebuilt atleast once) or was it standard on some XU9 blocks, prehaps very early or very late ones?

 

Are there any advantages to retaining this stud setup over the usual bolt arrangement, or indeed any disadvantages? Just trying to work out why it would have been done this way, and whether to keep this arrangement or to remove the studs (threadlock dependant) and revert to using bolts as normal.

[welshpug 1,626]

well not a direct answer to your question, but the XU7 bottom end I have been taking apart is all bolts on the mains.

[Anthony 1,000]

Had a closer look at the block this evening, and I'm convinced that it didn't leave the factory like this - the studs on #3 (where it would have been present from the factory) are a different colour to the ones on #1/2/4/5, suggesting to me that they've been added at a later date. The question remains though - why?

 

well not a direct answer to your question, but the XU7 bottom end I have been taking apart is all bolts on the mains.

As are XU10's, or atleast certainly the ones that I've stripped (XSi, S16, and GTi-6).

[base-1 17]

Studs with nuts are better, as you don't create twist all the way down the shank when torquing them up, because obviously the only bit that's turning is the nut at the top, which means yu get a more reliable torque setting and less stress in the fastener. They *could* be ARP or similar perhaps? Although not replacing #3 seems a bit pointless if this was the case - so either the company don't bother supplying it (surely ridiculous) or whoever built it didn't bother fitting the middle 2 (was any of the rest of it badly built? )