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Valve Guide - Major Failure --Why?


FB73tii

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Why would a new valve guide shred and puke itself out the air horn of my DCOE? I am talking pieces of ripped, curled up bronze.

M10, E12, 11:1, 45DCOEs, +1mm valves, dual springs, TI retainers, shaved keepers (to keep valves from rotating), 316, KM Cams rockers--all new valvetrain parts.

Valve job and new guides done at local shop. Piston/valve clearances checked, rockers and cam mated using JG BR30 and moly paste, engine run in on dyno (12 pulls to 8K).

For 20 minutes engine ran great on track, hot oil 60 psi, water 180 F, Brad Penn 20W-50 oil 240F, AFR about 13, pulled strong to 7.5K. Slight stumble, big puff of smoke, shut it down and came in on the hook.

I am looking for knowledge of people who have BTDT. Will know more when I pull head tomorrow.

TIA, Fred '69 & '74tii

--Fred

'74tii (Colorado) track car

'69ti (Black/Red/Yellow) rolling resto track car

'73tii (Fjord....RIP)

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For a race motor I give them a little extra ream, Some machine shops tend to give them a little too little tolerance, which is ok for a street engine but not for a race engine which may not have any run in time .

72/2002 Inca

72tii/2002 "Apple"

70/2002 "Five "

73/2002 "Freeda"

2007 Lotus 7 Replica

2011 Ford xr6 Ute

85 E30 325

70 1600-2 "Orange"

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Thanks. Surprising since this shop caters to local SCCA racers and knew I was buidling a race engine. So you think it siezed and the cam/rocker pushed it out? The valve lock on the rocker was moved a good 1/2", but is still tight on the shaft. --Fred

--Fred

'74tii (Colorado) track car

'69ti (Black/Red/Yellow) rolling resto track car

'73tii (Fjord....RIP)

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Any chance you hit a valve? You might have bent it right at the guide with the valve open then when it tried to pull back into the guide it would have split the guide. Your 1mm oversize valves might have hit the step in the valve relief on the piston. They are usually cut for stock diameter valves unless you spec them otherwise. When you checked piston/valve clearance by turning it over by hand you don't take into account small amounts of rod stretch and valve slop in the guide. A .001" here and .001" there and you could have a problem. With the head off you should be able to see the whittness marks ( I doubt it happened in just 1 cylinder.

1970 1602 (purchased 12/1974)

1974 2002 Turbo

1988 M5

1986 Euro 325iC

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Thx. The valve relief pockets are actually quite large on these pistons and there is plenty of radial clearance.  I checked V/P clearance both with checking springs and modeling clay. With input from my parts supplier (a well known '02 supplier) we felt the V/P clearance while on the tight side would be OK. The pistons were spec'd by the supplier knowing what valves I would be using as they supplied them as well. As you said, when I pull the head tomorrow morning I will see if there are witness marks on that and the other pistons. Will post some pics tomorrow night. --Fred

Edited by FB73tii

--Fred

'74tii (Colorado) track car

'69ti (Black/Red/Yellow) rolling resto track car

'73tii (Fjord....RIP)

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Possible failures. Ranked in order of likeliness.

 

There was not enough interference between the new guide and the head.  It pressed too easily when the shop put it in.  If this happened, the head is most likely junk.  The boss will be beat to tears.  This can not be fixed without alot of very precision work.  

 

The piston hit the valve, the valve bent and kinked in the guide.  The guide broke and pieces came out a trumpet.  This is kinda a tie from the top one.  You're running 11:1 and 1mm over valves.  there's a good chance for piston valve makeout session.  Depends on how sure you know there was clearance.  

 

There's not enough clearance between the retainer and the top of the valve guide/stem.  Depending on what guides were installed and coil bind etc.  If the machine shop replaced the guides and left them tall in the seats. Then at high revs, the valve retainer will float on down and start taping the guides.  Probably would have shown itself on the dyno though.  Starting to get into wishing and hoping.

 

There was not enough clearance between the valve and the guide.  Highly unlikely.  These clearances are pretty standard.  The 2002 doesn't use "tight" clearances by modern day standards and has nice large supportive valve stems.  Unless these 1mm valves had some custom stem diameter or were +.001" stems, then this is the unlikelyist of all.  SBC's run a smaller stem with a valve head almost 2x as wide using the same clearance with alot more side thrust and do not suffer any failures.

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Some photos below. Can't see the valve guide hole clearly because valve head wedged into head. One of the six remaining good valve pockets shows witness marks, the other five are clean. Hard to tell but does not seem to have witness marks on the valve pocket of the failed intake valve. Cut lines are from cutting the modeling clay.

Don't have specs on my V/P clearance, spring height,  clearance etc. with me at the moment. Will post in a few days.

Interesting to note that the valve broke at the lowest of the three valve keeper grooves. Hard to know if this happened first or after failure began. Cylinder wall has some damage, I'll need a new E12 head, piston, block and valves minimum. Will have to inspect rocker that took the hit carefully.

Do the photos give indication of posible failure mode? When I tear down the head I'll look carefully at all the components for additional witness marks.

Thanks for the input--Fred

 

post-36969-0-65872600-1378005309_thumb.j

 

post-36969-0-50167500-1378005355_thumb.j

 

post-36969-0-26510300-1378005373.jpg

 

post-36969-0-38120800-1378005407_thumb.j

 

post-36969-0-82795300-1378005435_thumb.j

 

post-36969-0-50696500-1378006112_thumb.j

 

post-36969-0-79597800-1378006134_thumb.j

Edited by FB73tii

--Fred

'74tii (Colorado) track car

'69ti (Black/Red/Yellow) rolling resto track car

'73tii (Fjord....RIP)

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Thx. The valve relief pockets are actually quite large on these pistons and there is plenty of radial clearance.  I checked V/P clearance both with checking springs and modeling clay. With input from my parts supplier (a well known '02 supplier) we felt the V/P clearance while on the tight side would be OK.

 

Ouch, Fred - that bites. When you have a moment, share your numbers on piston to valve clearance (always looking for reference). -KB

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Thanks to all for responses. Ken, just sent you a note on the head. Daron, thanks for the reference to the block. I spoke with my friend Roy Hopkins in Rochester this morning and he happened to know of a block for sale not 20 miles from where I am this weekend (Watkins Glen NY). Drove to a barn out in the country and picked it up for $50 this afternoon! Now I just have to see if Ross Racing Pistons can cut me another piston on short order. Marshall--yes, this has been a long road. At least the car went like stink for that 20 minutes, passed a number of Italian cars--180 RWHP in a 2000 lb car works pretty good :)

 

NOTES: the tip of the valve is still held by the keeper in the retainer. Will be interested to see the fracture pattern when I get it out. Also for Ken, will post V/P specs. I mapped the cam lobes and lift at 1 deg. increments, will post those graphs as well.

 

Thanks,

Fred

--Fred

'74tii (Colorado) track car

'69ti (Black/Red/Yellow) rolling resto track car

'73tii (Fjord....RIP)

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