Dyno mystery. Need your help

[2mAn]

Its all in the name... Nuke.

I'll see myself out

[dvallis]

Owwwwww! That hurt! : - )

[dvallis]

Been starting at this pic for a while, wrapping my brain around what happened. When the bolts came lose, belt and outer shell of cam moved clockwise. Valves opened later with respect to TDC. We got maximum retard. (Me and the cam)

The nuke gear can only move 6 degrees (I think) due to keyway length. Can't tell since I'm not at the shop. Each cam degree equates to two crank degrees, so we were at 12 degrees retard. That's a stupid amount but retard increases intake valve clearance we may be Ok.

[nando]

Thanks for the tip nando. We might keep the cam gear and dial in a bit of mechanical advance. How much does the M20 stock cam seem to like? We are running 284/272

I have the same cam. I think I started at 0 and maybe have 5 degrees now? It's been like 10 years since I've touched it though.

[dvallis]

Thanks Nando. 5 CAM degrees or 5 CRANK degrees?

[digger]

I have the same cam. I think I started at 0 and maybe have 5 degrees now? It's been like 10 years since I've touched it though.

IIRC you went 5 degrees of retard ?

i think Tinkerputzer also with 284/272 with 3.1L found best was a little retarded (4 degrees).
https://www.r3vlimited.com/board/for...64#post5789087

i ended up with 5 to 8 degrees of advance and found it was best power across all rpm but that's not the norm (unless the cam duration is a little excessive)

there is no universal rule

[moatilliatta]

You could get an offset dowel pin if you don’t want to run the adj gear.

[nando]

IIRC you went 5 degrees of retard ?

i think Tinkerputzer also with 284/272 with 3.1L found best was a little retarded (4 degrees).
https://www.r3vlimited.com/board/for...64#post5789087

i ended up with 5 to 8 degrees of advance and found it was best power across all rpm but that's not the norm (unless the cam duration is a little excessive)

there is no universal rule

yeah, could be, I honestly don't remember. I could pull the cover off, but we all know that's not gonna happen, lol. I do know I tried both advance and retard, then settled on something that had the biggest area under the curve. That's where I met Steve (hoveringuy) and really wanted an engine with full variable Vanos...

The disadvantage to SOHC is if you advance the intake, you retard the exhaust, and vice versa. So there's a pretty limited range that works. You just have to try it and see what works best for you. But I find it unlikely that the stock cam with whatever random timing you get with a particular bock/head/gasket combo is going to be perfect out of the box. So it's worth experimenting.

[nando]

You could get an offset dowel pin if you don’t want to run the adj gear.

You could, but that's rather permanent, and you have to already know what the best adjustment is first.

[nando]

Thanks Nando. 5 CAM degrees or 5 CRANK degrees?

TBH, I don't remember. I think probably crank degrees. I did a couple passes with a few settings, then left it at what made the best overall curve.

Also sorry for clicking "edit" instead of "quote". Ugh, this forum interface... lol

[hasa]

Any chance that valves have hit pistons and the retardation / being loose would be caused by that ? There may be many root causes. Loose bolts is one.

[TobyB]

The offset dowel washers are cool-
you oversize the hole, then use an offset washer to advance/retard the cam.
The domestics do this, so a set of washers is $6,99, and once you've done the
rudimentary machining, it's both very positively locked in place
AND pretty simple to change if you want to.

t
diy is sometimes less of a nuke.

[dvallis]

Update here. Was the Nuke Gear. We amputated and replaced with a solid gear 0/0 TDC.

Valves were not bent. (Wooooo!) Compression showed 210/211 psi on all 6. Ready for a re-tune, but I'm on vacation soon and our dyno guy is booked until after SEMA