Breaking cam chain guides

[Triiodide]

So this is driving me absolutely crazy. I have an e12 with a turbo m30b34 in it, running about 23psi on a knockoff gt3076. A few years ago I put in an Ireland engineering cam and valve springs when a rocker had broken and shortly after I did that I broke the stock cam chain tensioner rail, installed a new chain and guides and have had repeated failures over the past couple years. Has anybody experienced this? It seems like I'm the only one it's happening to. I even changed to a manual tensioner and made a crazy reinforced tensioner rail and after about 8 months it has yet again broken.. possibly the pivot pin on the bottom this time. It will be my 4th time tearing into it this weekend and I'm just looking for some input from people who have run boosted m30s. The cam from IE is very mild it's a 276 grind and 8mm lift iirc and their 90lb valve springs. Will attach pictures soon

[Triiodide]

https://photos.app.goo.gl/75bRTpESL4bmmsDD9
https://photos.app.goo.gl/3y1NsZGY9CEE3nL97
This final picture is the reinforced guide and the timing cover was cut to allow the angled steel to not interfere and used a manual cam chain tensioner.
https://photos.app.goo.gl/WXVrC1W8qUth8TzJ6

[turbodan]

While I have no suggestions for the cause, I dont think boost is a factor.

What kind of revs is it seeing?

[Triiodide]

Limiter is set at 6200 and it rarely hits it, previous breakages were after donuts in the rain not over 5k, a second gear pull to limiter, (spinning), third gear tires cut loose and let off at 5400. And this last one was a 4th gear pull let off at 5200. I'm thinking it has to be some crazy resonance going on. Last one was at 25psi 8 degrees of timing, pump gas. It makes crazy power but I'm wondering if there's so much cylinder pressure that when the exhaust tries to open it pulls the chain hard and then slaps the tensioning guide when it opens.. or fast changes in rpm.. it has a 10lb flywheel

[turbodan]

I don't see cylinder pressure doing it. The load on the timing chain is on the other side, even if the load on the chain varies it won't affect the tensioner side unless the chain was able to stretch and snap back like a spring. By far the greatest load is generated by the valve spring pressure and friction. Cylinder pressures are not a significant factor by the time the exhaust valve begins to open and the valvetrain has a tremendous mechanical advantage.

Do you have any pics of what it looks like assembled with a new tensioner rail in place?

[Triiodide]

The final picture I posted is the reinforced guide that is in now.. and broken. I am going to be tearing Into it tonight when I get home from work. I also just linked the Google photos hopefully those are all visible. This all started after the IE cam, rockers, and springs were installed after I broke both rockers on cyl 5. They broke at 23psi 4200rpm. I thought due to cylinder pressure the exhaust went then the intake after the gases had nowhere to go.. this was on the stock m30b28 with a mls .140. I put the IE stuff in the head and broke the guide about a month later. I put all new parts in it guide, chain, tensioner a few months later it let go again. Then I put in a b34 and put all the parts in that head. It all looked perfect yet I'm still breaking the guide. I thought the stock tensioner was over pumping after repeated fast revs doing burnouts and donuts so I put a manual tensioner and beefed up guide. Now 9 months later it's broken again

[Mike W.]

Terminology. You are breaking the tensioner rail, not the guide. The tensioner is rarely a problem. The guide on the intake side has been known to be a problem. But it doesn't appear to be your problem.

A bit of a long shot, but especially since you mentioned it's an E12, it might just have 350K miles on it. I'm not even sure how it would cause it, but I would at the least inspect, if not just preemptively replace the crank and cam sprockets, if original they might have a knife edge on them by now and have excessive play. Also I've heard OE tensioner rails have gotten very hard to find. Perhaps, and I'm reaching here, if you are having aftermarket tensioners fail, it might be them that's the problem, not the engine.

[Triiodide]

So my cam sprocket is new, or Less than 15k on it at this point, the crank sprocket is unknown mileage but when I compared it to another one it did not seem excessively worn but could possibly be causing an issue, I would think it would just wear the chain faster. I also actually thought that the aftermarket tensioner rails were the problem.. so I had found this very old rail from a dual row timing chain setup that I used and it also broke. https://photos.app.goo.gl/HJ9uCj96eDFezQBr9
https://photos.app.goo.gl/fan3F2zFhveupvfY7
This one actually lasted the longest and is considerably heavier and stronger appearing than any of the new ones.
My current one that just broke, which was "reinforced" which looking at it now there's many things I wish I would have done differently
https://photos.app.goo.gl/1qqQdSUhmfNU9Va47
https://photos.app.goo.gl/sKspoqGcfFHnq5Ss7
https://photos.app.goo.gl/wiRYxiHks3ahS4y49
https://photos.app.goo.gl/Z7k2GPcN12GMCPie7
The metal bracket on the back was tapped and screwed on the the back of the rail then the screws were welded in, as well as being welded on the bottom where the pivot is as well as on the top where the piston pushes. I did it this way to try to not melt the plastic material that the chain rides on but it seems as if the rail flexed enough to snap the steel off the bottom where it was welded as well as broke two of the three screws securing it on. It was making a hell of a noise hahaha, I'm lucky the last one did not break or that whole piece could have potentially fallen as the inner section of the timing cover has been cut to allow room for reinforcement from the tang the tensioner pushes on to be supported directly to the back of the rail. A side note is that the material the chain rides on is showing almost no signs of any wear. As of right now I'm still unsure on what I'm going to do to solve this, or even the reasoning for them breaking in the first place. That rail that is in three pieces I put the center section in a vice and bent it close to 45 degrees before it broke. Which makes me think there is some crazy resonance going on that is causing it.

[marc79euro645]

Just spitballin here, I have been fighting interferance with m30b35 pistons in an m106(basically a m30b34. using an .170 mls. I tried several cam timing setting, claying the pistons to be sure of my clearances. I found retarded timing caused exhaust to hit piston, advanced caused intake interferance. I ended up setting cam straight up, dowel holes aligned. If you're having either valve hit piston, stopping cam rotation momentarily, the chain would snap tight on tensioner. Where is your adjustable cam gear set?

[Triiodide]

The thick head gasket was on the 2.8, I had slotted the gear to get close to OEM cam timing but ever since I dropped in the b34 I put a new stock cam gear and is using a Goetze stock style gasket. I actually compared it to both an Elring and a Victor reinz and the Goetze actually had the widest fire rings and it's clamped on with ARP studs. I shouldn't have any issues with interference. On the b28 the very first time the tensioner rail broke it jumped a tooth and nothing hit, then again that was with a thick gasket. But those were even piano top pistons where the b34 are dished. After putting on a new chain it's never jumped when the guide has broken any of the following times. I also double checked and turned over the cam and theres no signs of any binding, it turns over smooth. Definitely up for hearing anybody's spitball ideas because I'm out of them

[marc79euro645]

The valves hit the piston outside of the dish, very close to the edge. My m106 pistons had marks from interferance. I was surprised it didn't bend the valves, but they all checked out by gasoline in the head upside down, when I had it off. I think the vertical position relative to bore must have saved the valves. The imprints were maybe 1mm deep.

[turbodan]

Any news?

I would pull the cam, plug in a stock B35 cam and see what happens. Best thing about boost is that you don't need radical cam timing to make power.

[Triiodide]

https://photos.app.goo.gl/foHNJYMpa8pHp4To6
https://photos.app.goo.gl/4mKU3FtfLwM3CLdx8

This is what is done on a new rail now. I have a b34 cam in a head still but it sure is a lot of work to swap it over to this one. My old b28 cam is cooked and I'm guessing the b34 cam I have is pretty worn too. This one from Ireland engineering is supposedly just a slight increase over a b35 cam, the b28 cam had about the same lift as this and all the other cams have slightly less lift if I remember correctly, and only a little more duration on this IE cam. Supposedly it was one of their 270 grinds that came out to 276 which is right what I was looking for. Great idle, tons of torque and still makes power up to 6k. If this one breaks again I'm going to go back to a stock cam..maybe even the springs too and just turn down the boost. I really don't want to have to do that but I'm so tired of breaking the same thing over and over.

[turbodan]

No need to turn down the boost. Whatever the cause is, I'm sure that's not a factor.

Weird failure to have though, a real head scratcher.

[Triiodide]

Well it's back together again and running flawlessly. For how long who knows . Im really starting to think it's from rapid rpm changes because every time other than this last one has been when its been spinning the tires and repeatedly pedaling it so it doesn't just sit on limiter, that and the very light flywheel makes it rev from 4 to 6k and back very quick. It sure would have to smack that rail hard though to break all of these. I'll update this again if it continues to grenade. Wish me luck hahaha.

[Triiodide]

I'd like to edit my posts to link the photos in a way that shows up, but can't seem to figure out how to make that happen from my phone.

[Triiodide]

Well I'm here again a year later. 99% sure the tensioner rail said see ya later bud once again. Have yet to pull it apart but it definitely is making bad noises and jumped a tooth on my way to work today.

[Dirtym30]

This must be a fast car. I have mine running at 10 PSI and its plenty fast.

[Triiodide]

This must be a fast car. I have mine running at 10 PSI and its plenty fast.

I'll be honest it's stupid fast, and a bit scary even. It has a pulsar 3584 now and water/meth. Lays rubber in third from 50mph for a looong ways with 225s. I pulled my tensioner piston out and one of the tabs was broken off yet again, I had thought the tensioning rail had maybe just slipped off so I turned up a 3/4" piece of steel round stock and made my own tensioner piston as they are no longer available and the fit doesn't need to be as tight because I'm using a manual tensioner now. I put it in and got it adjusted, it seemed good at first but it's already loosened and rattling again so there's something wrong inside still for sure, I ran out of adjustment and the new piston is bottoming out on the timing cover. Going to come apart either this coming weekend or next.

[Martin in BellevueWA]

Are both timing gear teeth worn? New sprockets and timing chain might help.
I had an ireland 284 cam go soft as the hardening wasn't good. Have a look at the lobes. Can't see that causing the guides breaking, but still.

[Triiodide]

Over all of the failures I've replaced the chain twice and installed a new cam sprocket, it's had two different engines with this same failure and both crank sprockets look very comparable to a new one but I have yet to install a new crank sprocket. I feel it's unlikely that's what is causing it. Cam still looks pretty good thankfully, no hard surfacing wear yet, although I keep thinking that the cam itself may somehow be contributing to the problem. Still haven't decided on how exactly I'm going to proceed until I see everything apart again.

[Triiodide]

Well, it looks like I reinforced the guide well enough now it snapped the pin off in the block instead. This time it's definitely getting a new crank sprocket, as long as I can manage to get this pin out.