This is pretty embarrassing but I installed what I'm guessing is an AAZ injection pump bracket on my AHU TDI. I had ordered it from ebay and had it machined to accept a land rover pump (mTDI) and didn't notice it was missing the part of the cast where the small timing belt roller (028 109 244) bolts on. How important is the roller? I wouldn't normally even ponder this and I am going to get the correct part machined, but it has me wondering how necessary it is considering there was a model without.
Thanks.
The camplate profiles for the direct injection pumps is quite a bit more abrupt and has higher lift than typical IDI camplates. That more abrupt pressure rise makes a more significant load on the timing belt. The added roller gives better wrap around the pump sprocket (and the cam) making it less likely to jump time. It probably will not jump time without the added roller. It just depends on how comfortable you are with risk. It also probably wouldn't jump time at the cam, just at the pump, so piston/valve contact is unlikely from such an event.
I would mention that I am sure that the VW engineers didn't change the pump bracket casting and add the extra roller whimsically. The load on the belt without the added roller must have exceeded what they considered safe for the TDI pumps/engines.
I agree I'm sure it is there for good reason and I only posted after I found at least one example online of someone running their AHU as such. I just fired everything up and things ran alright. I don't want to run it like this for an extended period but it would be nice to get my Vanagon from Portland to Seattle where I can continue working on it and get the correct AHU bracket modified and installed. It would be a huge shame if I put a [bigger] hole in my wallet.
Thanks much. I'll be sure to post if I grenade it.
I got the correct AHU pump bracket machined and mounted today, went for a test drive and things look happy. For reference I ran with the AAZ mount and no roller for 900 miles (two trips in the vanagon). I will say the belt looks more stable now, and I noticed without the roller that the tensioner alignment mark would sort of blip and move as the engine was running. With the roller on the belt the tensioner alignment mark is rock steady now.
... cause often its one of the "everything"s that fail in advance of the timing belt... tensioner, rollers, waterpump. Engine mount bolts.