Hi Guys,
I'm having a really tough time with a 454 I just had built and I'm in need of some advice. I picked up a 454 on OSO last year that didn't turn out to be what I was hoping so I decided to spend some money at our local machine shop and put it right. I've now had the engine out several times as it keeps bending valves after about five minutes of run time. The shop said all they did was disassemble and clean the heads but I didn't have this problem with the engine before I had it rebuilt. I'm running out of ideas and I'm concerned that the machine shop or I might doing something wrong.

The engine is a Dart Big M block with Dart Iron Eagle 308 heads. It has a forged steel GM rotating assembly pistons are forged federal mogul forged and give the engine a 9.3:1 compression ratio. Valves and springs are the same as what comes in a Dart 308 from the factory with positive valve seals. The cam is a Crane 132561 with crane hydraulic lifters and crane 1.7 roller rockers. Ignition is a thunderbolt IV V8-HP and timing is set consevatively at 10 degrees BTDC for break in purposes. The carb is an edelbrock 1410 stepped up to richest jetting on the chart (12%), The engine is in a Pachanga 22 with regular Stainless Marine exhaust and still has the original vernalift mufflers in place. The fuel tank has about 60 litres of 91 from last october that was stabilized and about 100 litres of fresh super and a can of SeaFoam additive.

When I first fired the engine I immediately brought it to 2000 rpm to break in the camshaft and the engine fired right up and ran for about 10 mins. Lifters took a couple of minutes to completely pump up. After about ten minutes the engine made a nasty mechanical noise (valve touching piston). I pulled the engine and returned it to the machine shop and it had bent the exhaust valve on number 1. They repaired it and I reassembled and installed the engine.

The next attempt was this week. Fired the engine up again and ran it at about 1600 rpm to finish the cam break in. I set the timing at 10 BTDC for 30 total timing and took it out for a drive. The engine backfired through the carb once as I tried to pull it up on plane then pulled up nicely to 2800 rpm. I varied the throttle over the next minute or so until the nasty sound returned and the engine started missing. I limped back to the dock and pulled the boat. this time I lost #1 exhaust valve again and cylinder had 0 lbs of compression. # 5 also kissed this time and was down to 90 lbs of compression. The machine shop said that there was a lot of gummy build up on the valve stems and said it must be the old fuel in the tank causing the problems. I have a tough time with that as I've had many engines with a little bit of last years fuel in the tank run through it just fine.

I'm really lost at this point and my patience is wearing very thin. The shop assures me that the valve clearance is fine but I'm having trouble believing them at this point. I'd appreciate any good advice as to where to look next. Thank you for any light you may be able to shed on this for me.

Sounds like it might not have enough valve guide clearance. When it starts to heat up the valve hangs open and the piston makes contact with it.

I'm about 99% sure that you have the timing chain installed incorrectly.

first place i would start is your valve springs. the springs that come on heads are a generic spring because not every head builder can make a spring to match every cam on the planet. get the right springs to match your cam. check your guide clearance. do you see and heat evidence on your valve stems?

Get to a other machinist NOW!

You either have too little piston to valve clearance or the valve is hanging up as already submitted.

The part I'm having trouble with is that the guy took it back apart and then reassembled it without fixing the problem.

This is a perfect example of why folks need to establish a relationship with a QUALITY, performance based, machine shop!

Good luck.

I'm betting the machinist never "degreed" the cam.

I had asked yesterday if maybe the cam was off a tooth and he showed me the lifter position with the timing marks and said it was almost impossible to get that wrong. When it's at zero is apparently exactly where # 6 changes valve openings as well. He told me that you can see that it is set up properly if it moves one valve on #6 immediately when you move off 0 one way and the other valve on #6 if you move the other. Can you tell me how the could have installed the timing chain wrong? I have used these guys several times in the past to build 350's and even once to build a vintage Jaguar XKE engine and this is the first time I've had any issue with them.

Sorry forgot to add that they clayed the top of the piston after the first incident and there was 300 thou of clearance.

There was no evidence of heat on the valves but there was a lot of kind of gooey carbon build up for an engine that had run for such a short time.

That sounds like a lot of valve to piston clearance.

Here is my thread about the issues I had with #6 and #8 cylinder. Not the same but similar issue.
Maybe wrong Mark/Gen head gaskets?

Another valve meets a piston - Boatfreaks