IMS Sprocket Pinning Question
05-11-2024, 12:07 PM
#1
IMS Sprocket Pinning Question
When I disassembled my M97.21 engine I found Bank 2 cams were perfectly aligned, but Bank 1 wasn’t. Out by 8.8 degrees at the crank, or 4.4 degrees at the cam.
So I started to inspect the IMS. I see no reason why the front and rear sprockets need to be aligned with one another as there is a lot of room for adjustment when setting up the cam sprockets, however this guy think it’s important. Start around 0:50 seconds:
Because I found my Bank 1 cams out of alignment, I decided to check the IMS. It was out. Couldn’t really measure, but it looked like a difference of about ¼ tooth between front and back cam sprockets. That works out with 20 teeth 18 degrees apart, about 4.5 degrees at the cam.... pretty much exactly the same as I measured as mentioned above. Could it have slipped? And if it did, why didn’t it keep slipping and damage valves, pistons etc.?
In the video he mentions all three sprockets needing to be pinned. LN Engineering only mentions pinning the main sprocket, not the other two (cam) sprockets. I think all three should be done, even if it’s a weld (somebody with a TIG as my MIG would make a messy job) on the cam sprockets and a pin on the main sprocket. A little nervous about welding as the heat may loosen the press fit a bit even though the weld should hold it. I feel comfortable pining all three the way it was done in the video.
Thoughts?
So I started to inspect the IMS. I see no reason why the front and rear sprockets need to be aligned with one another as there is a lot of room for adjustment when setting up the cam sprockets, however this guy think it’s important. Start around 0:50 seconds:
Because I found my Bank 1 cams out of alignment, I decided to check the IMS. It was out. Couldn’t really measure, but it looked like a difference of about ¼ tooth between front and back cam sprockets. That works out with 20 teeth 18 degrees apart, about 4.5 degrees at the cam.... pretty much exactly the same as I measured as mentioned above. Could it have slipped? And if it did, why didn’t it keep slipping and damage valves, pistons etc.?
In the video he mentions all three sprockets needing to be pinned. LN Engineering only mentions pinning the main sprocket, not the other two (cam) sprockets. I think all three should be done, even if it’s a weld (somebody with a TIG as my MIG would make a messy job) on the cam sprockets and a pin on the main sprocket. A little nervous about welding as the heat may loosen the press fit a bit even though the weld should hold it. I feel comfortable pining all three the way it was done in the video.
Thoughts?
05-19-2024, 11:26 AM
#2
No responses but judging by the number of views, there does seem to be some interest. So here's an update:
I'll just re-watched that video and I may have misunderstood. I thought the guide rod was supposed to be nestled between gear teeth at both ends. Now it looks like the rod is nestled between gear teeth at one end and is sitting on top of a gear tooth at the other. That more or less matches up with what I found, so maybe mine’s OK.
If my gears didn't slip on the shaft then why was Bank 1 cam timing out? My best guess at this point is the assembly person overshot getting to TDC by little, and then rotated backwards to get there and then adjusted the cam sprockets. Chain tension would be all wrong thereby affecting the adjustment.
Regardless I intend to pin all three sprockets as I don't want to take a chance on any slippage (no welding as the heat may loosen the original press fit). Gears can slip. See this video starting at about 0.40:
I'll just re-watched that video and I may have misunderstood. I thought the guide rod was supposed to be nestled between gear teeth at both ends. Now it looks like the rod is nestled between gear teeth at one end and is sitting on top of a gear tooth at the other. That more or less matches up with what I found, so maybe mine’s OK.
If my gears didn't slip on the shaft then why was Bank 1 cam timing out? My best guess at this point is the assembly person overshot getting to TDC by little, and then rotated backwards to get there and then adjusted the cam sprockets. Chain tension would be all wrong thereby affecting the adjustment.
Regardless I intend to pin all three sprockets as I don't want to take a chance on any slippage (no welding as the heat may loosen the original press fit). Gears can slip. See this video starting at about 0.40: