Tomei Poncam Broken!

[Waldo]

hey guys just wondering if anyone out there using tomei poncams in their rb20 have ever snapped one in half

i was driving down the road and gave it a bit of squirt then it sounded like i lost a cylinder...so when i got home i checked for coilpacks and all the usual stuff (ignitors, sparkplugs) and then did a compression test...cylinder 6 read 0psi i took the rocker covers off and cranked the motor over and i noticed that the inlet cam was completely snapped in two pieces right where cylinder 6 valves start so the valves werent in operation....the motor is still in good nick nothing wrong with the valves nor the piston...but im just curious on how strong these poncams are, if a camshaft that is around an inch thick of solid steel can just cleanly snap in two it must have been a manufacturing defect or something. i dont know.

[JCMarshall_Law]

Snapped cam?!?!? WTF?

how long were they in the car?

Still they should not snap,

Pull it out and see if it was a fatigue failure (looks a bit like rings in a tree trunk at the edges if you are look end on),

Were they staight? (hard to tell now)

Was something not alligned correctly? (hard to miss-align cams I know)

Were all the tolerances / torque settings on the cam retainers correct?

You may have a case to claim faulty manufacturing.

My 2c

Edited February 14, 2006 by JCMarshall_Law

[Beer Baron]

cams are very easy to snap. i can almost bet on the fact it was an installation problem. either incorrect torque, or torqued up incorrectly (ie in the wrong order). or the caps were possibly not perfectly positioned (swapped around) when being torqued up.

[Waldo]

they were installed correctly with the torque settings used out of the rb20det workshop manual..they were brand new and were in the car for about 6000k's...and no none of the caps were swapped around i had them layed out perfectly where they came from...my mechanic thinks someone had dropped them hard in transport which might have put a hairline crack through them that was not visible to the human eye

[Scooby]

i'd have thought the same as the Baron, did you install them yourself? if a hard drop in transport could put a hairline crack in a cam then it won't cope with the stress of being a bump stick, hard drop or not. and if it was enough of a hit to do that then you prob see a mark on the cam...a big one.

was it the same head ?

Edited February 14, 2006 by Scooby

[crack]

take some pics and put them up. did one or some of the bearing surfaces "nip" up. i vaguely remember roy (i think) had a problem with bearing sizes causing one to seize a bit

[Blitz]

This is about the 5th time I have heard of such problems with poncams

[Wazz]

This is about the 5th time I have heard of such problems with poncams

<{POST_SNAPBACK}>

hmm this is rather wierd.. first time i have ever heard of a cam snapping in 2.. how ever 5th for blitz :S

i dont think i'll buy pon cams after hearing this

[carl h]

strange, i would never expect this to happen.

perhaps the oil passageways in the head are a touch dirty, thus leading to poor oil flow, happened to a friend with a rb25det.

glad i stepped it up to the procams....

[Beer Baron]

i dont think it's unique to poncams. i've heard of other brands of cams snapping, and even in other models of cars. but like i said, it's nearly always a small installation problem, or it can be a bearing problem. but it's possible it could have been damaged in transit, or have suffered a manufacturing fault.

[JCMarshall_Law]

cams are very easy to snap. i can almost bet on the fact it was an installation problem. either incorrect torque, or torqued up incorrectly (ie in the wrong order). or the caps were possibly not perfectly positioned (swapped around) when being torqued up.

<{POST_SNAPBACK}>

Wow, I had no idea, I have not seen a snaped cam before, although I'm not a mechanic and I don't play with cars everyday. Interesting.

Good to see people seem to agree with my ideas on the failure.

[Shaun]

Ive heard of heaps snapping too. There's no warrenty against this either, as they believe its always an installation error; ie torquing up in wrong order or with the incorrect orientation of the lobes. Bummer.

[darrinspencer]

I sold a pair of stock Rb26 cams to guy once

His "Factory" Rb26 inlet cam snapped.

[R31Nismoid]

well until we get pics its a bit hard to say poncams are dodge when there are 100's upon 100's of people using them.

Every one i've heard of has been incorrect installation

[Sydneykid]

Hi Waldo, that is most unusual. Snapping a long, straight 6 camshaft is remarkably easy, I have seen quite few. But it usually happens during, or very soon after, installation, not 6,000 k's later. It will be interesting to se if it is twist break or a straight side load crack. An inspection of the surrounding parts may reveal something else.

I will be very interested in what you find out.

cheers

PS; you where very lucky that the valves were closed, not open, when the cam broke, otherwise bent valves would be the result.

Edited February 15, 2006 by Sydneykid

[carl h]

well until we get pics its a bit hard to say poncams are dodge when there are 100's upon 100's of people using them.

Every one i've heard of has been incorrect installation

<{POST_SNAPBACK}>

yeah i must concur.

i installed my own cams according to the jpnz manual (that i forked out 132$ usd for mind you) and following the proper removal and install instructions along with torque specs i havent had a problem yet.

[Scooby]

It will be interesting to se if it is twist break or a straight side load crack.  An inspection of the surrounding parts may reveal something else. cheers

<{POST_SNAPBACK}>

a twist break? that'd be huge torque. i'd have thought the tooth belt would strip before that happened.

[rev210]

Tensioning up the the bolts must be precise. If your torque wrench cost you less than $100 you need to be carefull. If it cost less than $50 maybe thats your problem.

When I did my cams in the shed I took the factory reccomendations and added a step in between at the last torque to be sure.

The cams are very easy to snap and even bend enough to weaken them so they let go 6,000kms down the track.

[Waldo]

yeah i tensioned the bolts up in the exact order of the manual to exactly the right torque...and i checked the oil feed fo the bearings where it sat and they are all fine...i will get a picture tomorrow and post it up it just looks like a complete snap in half as if you broke it over your knee..and iut snapped right halfway down cylinder 5 actual so only 1 inlet valve was opening in cylinder 5 and none on cylinder 6...and now one of the bearings has the slightest mark in it from where it broke and wedged itself..it snapped one of the bolts that hold the cam caps down aswell.

[rev210]

Broke a bolt you say?

I think it's probably the bolt that gave out then. The old bolts are a bit of a lottery when putting them back in, I broke one on mine on putting the cams back in. Next time I do a set of cams I will use new ones or ARP's, it makes sense really.