Bent Valve

[glb914]

I’m a longtime owner of a 1972 914. Recently, I pulled the engine to address some oil leaks and clean it up. New pushrod tubes and seals and aluminum pushrods to replace the steel ones. Everything back together and engine installed, went for a test drive, got a backfire at high rpm, not over revved. Carbs were syncronized when I started it before driving but now getting no reading on snail gauge from number three cylinder. Compression test, no compression. Pulled valve cover and the adjusting nut and valve keeper and one elephant foot were rattling around inside. I dropped the engine and pulled the head to find the exaust valve was bent and had put a small dent in the piston. The elephant foot was from the intake valve which was fine but the rocker arm was totally loose. I can’t figure out what caused this as it would help me to determine my next step.

The engine is a type 4 which started as a 1.7. In the early 70’s I had it modified with NPR 96mm P&C and 74mm stroker crank with Weber 44idfs. Valve sizes remained the same at 39 x 33. The NPR set was slip in and was installed without head gaskets, so cylinder surface to head is very small which caused them to slightly dig into the heads to seal. Aproximately 20,000 miles on the engine now.

So, here’s the dilemma. Many new choices for heads with many valve combinations, but only for 1.8 or 2.0 which would mean new P&C also. Or have my heads rebuilt with larger valves and keep my P&C (cheapest option).

Anyone have an idea of what went wrong? The valve adjusting nut not tightened, or weak valve spring, or lighter pushrods, bad timing, what about the broken elephant foot on the intake valve, or…

Thanks for any help or advice.

[Ohio Tom]

I have had similar happen.
the adjuster gets loose, or something falls apart. The pushrod falls out, but not all the way.
for one or 2 cycles, the pushrod rides on a high spot on the rocker and over lifts the valve once or twice causing collision with the piston.

[raygreenwood]

[Wreck]

could it be also caused by valve float , if you have a weak spring ? the pushrod riding up on the cup of the rocker arm . A long shot because you didn't have any issues with the steel pushrods . just throwing ideas out there.
I take it the pushrods were made the same length ?

whether you just replace the valve ,get a valve grind etc (cheapest option ) or get bigger valves and the heads slightly ported to match . Or just get a new set of heads from AA .
On a performance level the best choice would be their 2lt 914 heads with valves size to suit your cam/RPM choice . problems are ,you could most likely get spacers made to locate the 1700 size cylinders and you would also have to drill the cylinder tin for the different spark plug location .

If you don't want to drill the tin for new spark plug locations then the type 4 round port heads will work well .

double check that your 1700 heads haven't been opened up to suit 1800/2000 cylinders already . Slip in may have meant in the case .

all depends on budget .

[glb914]

Yes, pushrods were the same length as original ones (not original to 1.7 but sized for the cam and stroker). 20,000 miles no problems. Engine was professional build but 70’s technology. Shims between cylinder and case to compensate for stroker crank. I’m thinking either a weak spring or I didn’t tighten the adjusting nut enough. The top of the keeper has a pretty deep divot on one side and it popped off the valve so both rockers were flopping around in there, slight hole in the valve cover. Spring wasn’t broken.

Kind of thinking 1.8 heads with 44mm x 36mm and Keith Black 96mm P&C, just wish I knew what went wrong so it doesn’t happen with the new parts.

Anyone know a good machine shop for aircooled heads near Cleveland Ohio?

[raygreenwood]

[glb914]

No, not the same length as original 1.7 pushrod but same length as pushrods which were sized for the modified engine, 2143cc. Just wanted to replace the steel with aluminum to quiet it down a little.
No, original equipment length would be way too short.

[raygreenwood]

[mikedjames]

I had this when I was stupid enough to use stock wavy washers and clips to hold the rockers in place with elephants feet. The whole thing fell off the valve tip with the engine at full power climbing a hill around 55mph , chewed the valve tip slightly and wrecked the adjuster, made the engine backfire, shook the 4 dowel flywheel loose.

Went over to solid rockers, but in the end that valve gave way.
_________________
Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[udidwht]

Very well could be an adjuster screw not snugged down during valve lash check also. Or a less than stellar elephant foot (quality wise).
_________________
1972 Westy Hardtop/Type-4 2056cc
96mm Biral AA P/C's~7.8:1CR
Headflow Masters New AMC 42x36mm heads w/Porsche swivel adjusters
71mm Stroke
73 Web Cam w/Web solids
Dual 40mm IDF Webers - LM-2 - 47.5 idles/125 mains/190 air corr./F11 tubes/28mm Vents - Float height 10.45mm/Drop 32mm
Bosch SVDA w/Pertronix module (7.5 initial 28 total @ 3400rpm)
Bosch W8CC plugs
Pertronix Flamethrower 40K coil
S&S 4-1 w/Walker QP 17862
3 rib 002 Trans
185R14 Hankook tires

[raygreenwood]

[glb914]

ACN Heavy Duty Aluminum Pushrods, .410 lift cam, stock spacers, elephant feet adjusters from ACN (USA), Rocker studs were tight.
Nut came off exhaust valve, elephant foot off intake valve. Valve cover damaged inside).
Only time of running engine was to sync carbs and 2 mile test drive. I think I may not have tightened the adjusting nut enough.

[raygreenwood]

[glb914]

.410 lift cam.

http://vwparts.aircooled.net/ACN-Heavy-Duty-Alumin...p;CartID=0

http://vwparts.aircooled.net/Elephant-s-Feet-Valve-Adjusters-8-p/adj-elephants-ft-8.htm

Very high quality pushrods, not damaged at all.

[raygreenwood]

[txoval]

Those are CB style elephant feet adjusters, $39 for 8.

The authentic Porsche are about $30 each x 8

There is a difference in quality

[raygreenwood]

[Wreck]

I’ve over 25,000km on those ACN pushrods with cams of similar or slightly more lift , so far no issues with adverse wear of the rocker cups .

It may be a simple thing of not tweaking the lock nut tight enough . Easy to do , recently I didn’t tighten an inner nut properly , no idea I why I missed it ,on #1 rocker shaft and caused some adverse wear on the intake valve stem and adjuster . These things happen .

[raygreenwood]

[glb914]

Pushrod photos