Whaddya think? Bullet Roller. 279@50 500lb springs 4 seasons old.

That 2-cylinder engine must turn some serious RPM with that much cam.

Ouch

Tex

I'd bet some sort of harmonics issue.

It could have also been a bad core but that stuff usually shows up before that much time goes by.

Seems to me the radial cracks looks like a harmonic issue though.

My uncle had a 440 do the same. I think I remember him telling me the cam plug walked out, cam broke in 3 pieces, fell between the rods and ejected a few! Found a piece of the cam between the header tubes

I had one break like that from a #4 cam bearing spinning and breaking at that journal. The rear two cylinders were not opening or closing. Drove it all the way home like that. Still ran like a V6 just fine with slightly less oil pressure. It required full rebuild anyway.

Really strange looking pattern on the 2nd lobe down from the break.

Never saw one look like that before....... But I have to suspect its related.

So i'm thinking with this failure plus the other thread i have with the damper leaving marks on the crank snout, i need to replace the Damper to be sure i don't have a reoccurance. Anyone have a Summit Voucher theyre not using? $25 of your dollars is $40 of mine. every bit helps. thanx

Years ago my buddy would break cams on a regular basis in a high hp chevy small block. It was a harmonics issue - he was using a gear drive. A Jesel belt drive solved the problem.

What condition are the #1, 2 and 3 cam bearings? Have you measured them against the cam journal diameters?

I'm already running a belt drive.

Cam bearings all good. None have moved

that was the first thing I noticed, looks like a flat spot or somthing at the begnning of the ramp, looks like the same thing on the lobe nearest the dist drive gear, looks much lighter like a ghost mark.

ive had a cam break in 3 places before,cam was adjusted wrong was my problem

Looks like your picture of the cam bearing was taken from he crankcase side of things. The cam wears on the bottom. Reason why I asked about clearance as we had this issue in production 3.3 and 3.8 engines where the cam would break. In every case the cam bearings were worn out badly from scratches left in the cam journals from a previous production issue. The cam bearings wore at the bottom leaving the cam unsupported. Yes those lobes look strange to me too. Not sure how lobe wear relates to a broken cam - I've seen dog bones fail and the lifter rotates 90 degrees without ever seeing a cam fail from that.

Yeah well I can't get my phone in from the other side to get a pic. As you can see it's an aftermarket block so no big hole to look thru but fingering it, I can't feel any difference with my eyes closed doing the Stevie Wonder test.

I would see if you could find an 8620 cam core for the replacement, and verify with the cam grinder you absolutely have enough spring load to keep the valvetrain under control.

I would also be trying to figure out what caused that witness mark on the lobe.

I don't know what your combo is, but it's the kind of mark I'd expect to see if there was some minimal contact between an aluminum rod and the cam.

Since you have an aluminum block its also certainly possible that just before/after the cam actually let go it whipped around inside the cam tunnel, and that's just the mark that was left.
If so, there should be a corrosponding mark in the tunnel where the contact was made.

Is it me or has it been repaired...did you check it for straight before the in stall

that mark you're seeing on the lobe is just the effect of the light from the flash on what was probably a bit of water laden oil. i took that pic as i pulled it off the motor. we've had rain for the past few months almost non stop so most of my oily stuff looks milky. i've wiped it down & its gone now. The cam has had a minor repair as last season a roller wheel collapsed so i had it refaced. hence the side damage on that lobe. ive put a new cam in the hole, it seems to be free spinning but i'm going to visit my machinist this morning & have him cast his eyeometer & micrometer over it just to be sure.

I've been using a gear drive for the last 8 years with
no problems and I'm putting engine together now with one

Well I've been to my machinist, spent near on an hour n a half checking everything. All bearings are good, just a shy under 0.002 clearance. His conclusion is....replace the Damper & Cam. Well I have a new cam so it's only buy a new ATI.

thats what I would do

Did you ever mention what damper you had?

yeah maybe not but it was an ATI. Both my streetcar & racecar have an ATI, so it guess they have a best before date so its time to change. I did have a Fluid Damper in the early days, don't think i'll revisit them again. Had to cut that one off when it went south.

when i first started using this cam we found we had valve float. the specs that Bullet told us were just too light. i chewed out the lock area on the valves in the first season. i went for new valves & stiffer springs the next season & the ET dropped 0.1 on average. the valves are now looking good except theres a few bent ones after this happened.

the mark on the lobe wiped off with a rag. just milky oil with all the rain we've had lately. i have heavy dew in the mornings on all the steel in the shed. i'm sick of the rain. its winter here


The rods are Steel Molnars so no contact. The Cambelt drive actually controlled the cam quiet well when it broke. I was taking a passenger for a ride at the time, had just pulled second gear after the fronts had touched down when pop & we went into coasting mode.

Like I said initially...... Go for a cam made from an 8620 core(the copper colored ones).

i have a 23-709-9 comp cam as a replacement. its gold so i guess thats the type youre referring to?

Gold/copper.... Yes

For some reason I thought you had a small block.

What heads, springs, pressures, and rocker ratios are you going to run with that cam?

i have a set of Larry Smith ported -1's that flow 386@800 & a set of 1.6 ratio HS rockers, PAC springs that are 663lb spring rate. 13:1 comp ratio. The converter is 6k stall with 4.88 gears on 32x14 MT slicks. i think my combo is fairly well matched. unless you have some input you'd like to share?

I just wanted to see if you had an extreme rocker ratio and possibly not enough spring.

Sounds like you should be okay.

Better get that block squared up....

?? not sure i understand.