Technical > Matt Shaff's Engine Shop

Lost cam dowel - what to do?

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Dunc the Funk:
We had our blown methanol BBC freshened up for the season by a fairly well known hot rodder/race car builder here in the UK. There was not much wrong with it from last season, basically he just replaced the bearing shells. We test ran it for the first time last week, it fired up and ran well. After draining the oil we found some small non-magnetic particles in the oil filter. Not enough to really worry about but a bit puzzling. Some of them seemed to be aluminum & some looked like phosphor-bronze. When we checked the lash before running again, it developed a tight spot that got worse the more we looked for it, until it was pretty much locked up. We took off the blower & inlet & I noticed I could move the crank about 5 degrees without moving the cam. We took off the fuel pump & front distributor drive & found that the cam dowel was missing & the bolts loose which hold the drive & cam hub to the cam. It seems the builder did not torque them up enough. He agreed on that & stated that there definitely was a dowel in the cam. We have not been able to find the dowel. it was not in the sump. A more experienced builder & racer told me they do sometimes come out & the gear drive is so hard it can actually munch them up. We tightened the bolts, replaced the rockers one at a time, turned it over by hand & it seemed ok. We didn't run it because I could not get a dowel & also we were worried about where the bits had gone. So after that long story, my question is should we have it completely stripped, inspected & cleaned or just replace the dowel?

dreracecar:
Had an engine come thru the shoppe that someone used stainless socket head bolts for the cam gear, the bolt stretch was so bad that it looked like both coarse and fine threads on the same bolt.   If you are running a steel pan, place some magnets by the oil pump inlet to catch any steel floating in the oil before it goes thru the pump. fine particels thu the pump will get caught in the filter before it gets to the rest of the motor.
 Bronze filings could be from the Magneto gear

wideopen231:
Our TA/FC  did this fairly regularly. Mu guess was cam harmonics caused the bolt that where tight and had loc tit on them to come loose. A good way to keep check is Cranking compression will change pretty good amount. Record and when all cylinders show off about same amount its loose. As for dowel we went thru abunch on materials and finally just 1/4" ss rod(not bolt). Worse thing is sometmes it will break dowel and leave some in cam and its PIA.

 If dowel is out its in bottom of oil pan or chewed up. Who ever said gear would eat it is 100% right.   I would drop pan take a look around and let it rock after that.

Dunc the Funk:
We took the pan off & it is not in there. It's a Moroso 20385 ally pan with kickouts & rear sump. I think the dowel may have knocked the corners off the end of the distributor gear to make the bronze particles, it looks slightly worse than I remember. Incidentally I tried a 0.250" dowel & it's about 5 thou (guess) undersize. Should I worry about the idler gear bearing on the cam gear drive? It looks just possible that debris could get in it. I could maybe pull the hub & remove the cover to examine it.

dreracecar:
the cam, the gear, the dowel is "undersize"???

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