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Pushrod Popped off*** UPDATE with PICs

Posted by Filth and Greed Motors

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Pushrod Popped off*** UPDATE with PICs #1
Filth and Greed Motors Paul Gaylo Corning, NY, USA 1959 MG MGA 1500 1970 MG MGB GT	Posted: August 08, 2012 11:23AM Registered: 5 years ago Posts: 1,379

The next installment of the rebuild that never ends:

The issue concerns, what I believe to be, a slipped vernier cam sprocket. I have 100 miles on the engine and everything was just fine until my father called me indicating there was a problem when he was using the car yesterday. I haven't looked at the car yet, but he claims that driving along at about 65mph the engine all of a sudden (like a switch) started running differently. He described it as lumpy rough running versus how it was running right before the change. He also claims there are new noises along the lines of a periodic scuffing noise.

It seems to me that the symptoms point to a valve timing problem. This bothers me deeply. I spent particular attention to the timing chain area and read extensively about all the considerations for the assembly and degreeing of the camshaft. I also spent a considerable effort to loctite and torque the lock screws for the adjustable gear. I think I torqued these screws about 3 times with two different torque wrenches.

The only thing I can think of is one of the cam thrust plate screws backed out and connected with the cam sprocket and, as it was torn out of the block, moved the valve timing. The shred of screw is causing the scuff noise and now the valve timing is retarded. Of course these screws were loctited and torqued.

Oh well. Sounds like a teardown this weekend.

Edited 2 time(s). Last edit at 08/13/2012 08:28AM by Filth and Greed Motors.

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Re: Slipped Vernier Cam Sprocket #2
Steve64B Steve Opitz Phoenix, AZ, USA 1966 MG MGB	Posted: August 08, 2012 12:03PM Registered: 6 years ago Posts: 8,338

Paul,

I just went through that this spring when one of the bolts backed out of a timing sproket. If that's what happened to your motor, I think it's going to cause more than poor running. In my case it was a monkey wrench in the machine, tore up the entire timing assembly.

This build I went belt and suspenders... loctite and safety wire!

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Attachments:

Safety Wire Cam Gear.jpg (54.6 KB) –

Re: Slipped Vernier Cam Sprocket #3
Filth and Greed Motors Paul Gaylo Corning, NY, USA 1959 MG MGA 1500 1970 MG MGB GT	Posted: August 08, 2012 12:13PM Registered: 5 years ago Posts: 1,379

Steve-

Your engine blew right about when I was setting mine up so I was super careful when I did the timing chain stuff. I am sorta hoping that something stupid simple is wrong, but I really think the issue is slipped valve timing. The car runs too well for it to be anything else. I am lucky that the chain didn't break as the pistons would hit the vlaves and game over.

As it is, I cut notches in the cam to clear the big end of the rods, and if the valve timing slipped a full 20 degrees, the rods are probably tapping on the cam.

I can almost believe that the clamp bolts held, it was something else that got jammed up in there and forced a slip.

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Re: Slipped Vernier Cam Sprocket #4
Steve64B Steve Opitz Phoenix, AZ, USA 1966 MG MGB	Posted: August 08, 2012 01:19PM Registered: 6 years ago Posts: 8,338

Paul,

When mine went one of the sproket bolts dropped down into the crank gear at about 6K RPM. The front of timing chain cover was almost cut free by the chain. Both the crank and cam sproket were missing teeth and the meyham had clipped the heads off the two bolts holding the tensioner clean off. Only had minor contact of valves with internal surfaces... but replaced everything as a precaution.

In your case it could be that the bolts haven't backed out, just loosened. I don't know enough to know if valve timing being off by 20* might cause contact but now the intakes might be in danger of kissing a piston?

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Re: Slipped Vernier Cam Sprocket #5
Speedracer Hap Waldrop Greenville, SC, USA 1967 MG MGB "The Biscuit"	Posted: August 08, 2012 02:08PM Registered: 7 years ago Posts: 20,301

I never had one of these give any problems, but anything is possible. The biggest piece of advice I give folks on these units is to loctite the 1/4" bolts on the vernier and always, and I mean always torque the cam retaining nut before you degree, and adjust the cam, the high torque of the cam retaining nut will over power the 1/4" bolts in the vernier and change your cam timing, and possibly loosen them, if you torque the cam retaining nut last. Also, once you loctite something you have about 20 minute work time and after that don't go back and retighten it, you could possibly break the seal of the locite and nullify it's purpose to begin with.

Hap Waldrop
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Re: Slipped Vernier Cam Sprocket #6
Filth and Greed Motors Paul Gaylo Corning, NY, USA 1959 MG MGA 1500 1970 MG MGB GT	Posted: August 08, 2012 02:52PM Registered: 5 years ago Posts: 1,379

Roger that Hap. The cam nut was torqued way before anything was degreed since I was reading all about this around the time I did the work. I did the loctite and torqued and let the loctite tighten and did not go back to loosen anything.

I will pull it all appart this weekend and post a pic. Something went wrong.

Before I pull the front of the engine apart I will do all the normal diagnostics. I am praying the distributor broke inside or something. But the inductive tach is stable which shows consistent points contact in the dizzy. My dad pulled the valve cover to look for loose rockers or something wrong and didnt see anyhting obvious. It doesn't really run bad enough for it to be carb related. There is a remote possiblily of a vacuum leak or something. Reportedly the car still idles and drives, just very poorly. Sounds just valve timing to me.

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Re: Slipped Vernier Cam Sprocket #7
fast-MG.com Dave Headley Cortez, 4 corners, Colorado, USA	Posted: August 08, 2012 07:27PM Registered: 4 years ago Posts: 3,209

Could this be related to high runout in the crank sprocket? I ran into this earlier this year with a crank sprocket that came with a vernier set. When you get it apart, use a digital caliper to measure root of the teeth to bore. Should be within a couple of thou. The one I found was about .020"+.

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Re: Slipped Vernier Cam Sprocket #8
Bandit Racing Donald Dickey Illinois, USA 1963 MG MGB Racecar "#99 BRG Vintage Racecar" 1965 MG MGB Racecar "#10 Huffaiker/ British Leyland"	Posted: August 09, 2012 08:00AM Registered: 8 years ago Posts: 268

Dave

Can you give us what manufacture made the offending sprocket.

I use a different approach on locking the vernier in position. I set the timing then drill and tap a small 10-32 hole through both sections of the gear and use a SHCS locktited in place so it would have to shear the bolt to make any movement. I then lock the nut to the cam shaft.

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Re: Slipped Vernier Cam Sprocket #9
fast-MG.com Dave Headley Cortez, 4 corners, Colorado, USA	Posted: August 09, 2012 09:08AM Registered: 4 years ago Posts: 3,209

Don, it came with a vernier timing set I got from Basil. I don't remember that the crank sprocket was branded. I let him know about the issue and I posted about it here. The tip-off was tensioner oscillation as I rolled over the engine. Could have been a "one-off", but probably not. confused smiley

My conclusion is, every sprocket I use gets checked. It's quick and easy. devil smiley

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Re: Slipped Vernier Cam Sprocket #10
Filth and Greed Motors Paul Gaylo Corning, NY, USA 1959 MG MGA 1500 1970 MG MGB GT	Posted: August 09, 2012 05:46PM Registered: 5 years ago Posts: 1,379

FAIL

10 mins in the garage, found a pushrod that came off.

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Re: Slipped Vernier Cam Sprocket *** UPDATE with PICs #11
Filth and Greed Motors Paul Gaylo Corning, NY, USA 1959 MG MGA 1500 1970 MG MGB GT	Posted: August 09, 2012 05:50PM Registered: 5 years ago Posts: 1,379

Well it looks like a pushrod came off. I don't understand why yet. I suspect a stuck valve. The head was done by Sean Brown, and I was planning to avoid this type of thing. Maybe a valve seat came loose then re-set? I am pretty sure the lifter didn't explode.

I am a little curious about the different valve keeper heights. If you look carefully some are flush with the retainer cap, and some are proud. Not sure about this.

What other reasons could a pushrod come off? The clearance was set twice so far...

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Re: Slipped Vernier Cam Sprocket #12
dickmoritz Dick Moritz Philly 'burbs, PA, USA	Posted: August 09, 2012 05:53PM Registered: 3 years ago Posts: 7,223

Ahhh... But why? Improper adjustment? Adjuster left loose? Coil spring bind? Bent valve? Stuck valve? Revved to 10,000 rpm?

Inquiring minds want to know...

Dick

Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

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Re: Slipped Vernier Cam Sprocket *** UPDATE with PICs #13
Filth and Greed Motors Paul Gaylo Corning, NY, USA 1959 MG MGA 1500 1970 MG MGB GT	Posted: August 09, 2012 05:55PM Registered: 5 years ago Posts: 1,379

The exhaust on number 3 popped. I laid a straight edge across all the tops of the valves and they are all even. I don't think there is a chance the exhaust valve hits the block, I am .060 over and I cut reliefs in the block.

There is about .040 interference with the pistons should I have a full out failure of the valve timing gear.

The engine had about 100 miles on it, failed on a constant speed 65 mph run. Failed like a switch.

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Re: Slipped Vernier Cam Sprocket *** UPDATE with PICs #14
Filth and Greed Motors Paul Gaylo Corning, NY, USA 1959 MG MGA 1500 1970 MG MGB GT	Posted: August 09, 2012 06:00PM Registered: 5 years ago Posts: 1,379

There is no way it was over revved. The head is Sean Brown's. Adjuster was tight. Rotating the engine over it feels fine. It could be coil bind but what I have for lift shouldn't be outside what is acceptable.

.295 lobe lift, 1.5:1 rocker set up with good geometry. ~.016 lash.

I don't want to believe this, but it seems that the valve stuck somehow.

What do I do? Put it back? Pull the head?

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Re: Slipped Vernier Cam Sprocket *** UPDATE with PICs #15
fast-MG.com Dave Headley Cortez, 4 corners, Colorado, USA	Posted: August 09, 2012 07:19PM Registered: 4 years ago Posts: 3,209

Pull the head, disassemble, see what you find. Top end of pushrods look discolored. Was this like this at the beginning? Compare spring coil bind length to installed length for possible coil bind. Install retainers, no springs and make sure bottom of retainer can't contact top of guide or seal at full lift.

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Re: Slipped Vernier Cam Sprocket *** UPDATE with PICs #16
Steve64B Steve Opitz Phoenix, AZ, USA 1966 MG MGB	Posted: August 09, 2012 07:39PM Registered: 6 years ago Posts: 8,338

In my 2010 rebuild I noticed that the ridge in several of the keepers was too large to fit in the reliefs at the top of the valve stem. I ordered extras and picked and chose to find keepers which fit tight into the stem and retainer.

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Re: Slipped Vernier Cam Sprocket *** UPDATE with PICs #17
dickmoritz Dick Moritz Philly 'burbs, PA, USA	Posted: August 09, 2012 07:41PM Registered: 3 years ago Posts: 7,223

Roll the errant push rod on a very flat surface like a piece of glass to see if it shows any signs of being bent...

Dick

Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

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Re: Slipped Vernier Cam Sprocket *** UPDATE with PICs #18
Filth and Greed Motors Paul Gaylo Corning, NY, USA 1959 MG MGA 1500 1970 MG MGB GT	Posted: August 09, 2012 08:14PM Registered: 5 years ago Posts: 1,379

The push rods were blue to start out with, that was from seating the ends. I posted about the coil bind issues and after some measurements and checking it seemed that I was okay, but who knows.

As far as bending goes, I don't think that the errant pushrod is bent. I will bring it to work and indicate it.

I will pull the head to see what is what.

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Re: Slipped Vernier Cam Sprocket *** UPDATE with PICs #19
rhinsb Rich Hagon Santa Barbara, California, USA 1971 MG MGB GT "Money Pit"	Posted: August 09, 2012 11:04PM Registered: 6 years ago Posts: 1,167

That sucks Paul. I have the same setup so I'll be watching and learning.

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Re: Slipped Vernier Cam Sprocket *** UPDATE with PICs #20
Basil Adams About 12 miles from Sears Point, USA	Posted: August 10, 2012 01:27AM Registered: 6 years ago Posts: 5,972

Paul, With rollers, the geometry is always an issue. Look for a wear pattern on the valve tip to see if the roller was coming off of the tip. If it did, the back would over-articulate and the push rod would come off. Just a thought. Basil 707.762.0974 basiladams@yahoo.com

Basil C. Adams
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