[gtzero]

Hi All,

As most of you know, I recently put my re-worked head back onto my engine. I've been driving my car a couple of days now. And I noticed that when I get on it, there's a gravelly sound at around 5000rpm causing me to back off. Everything sounds fine up to around 5000rpm. What might this be?

I'll try and experiment tomorrow. Such as different gears @ 5000rpm. I've been a bit gentle with my car since I'm still a bit apprehensive about my handiwork. But the weather is dry and the sun is out. It's time to burn up some roads!

Thanks,

Manny

 

[Scott McDonald]

...there's a gravelly sound at around 5000rpm

Does it sound like ice being crushed/general grinding noise? I do. Mine is due to detonation. Did you do anything to the head? Was it deburred afterward?

I think rough edges could cause detonation, as could ignition timing. If it is detonation, I wouldn't "get on it" just yet, as you may inadvertently destroy a piston ring and/or piston. Then, you would have to drive the yellow "beater" in your garage!-BTW: What a beautiful car!

I don't know if being a tooth off would only cause detonation under load @ rpm above 5k. I would think being a tooth off would cause it to run crappy @ any rpm under load or not. Anyway, I would restab the distributor, after I checked it and made sure all my advance parts worked correctly. If after I did that, and there was still detonation-

If it is detonation due to rough edges on your head, I don't know if adding octane boost will lessen the occurence. I would try anyway, in hopes of narrowing what is suspect. If adding boost causes the grinding sound to disappear, or occur @ a higher rpm and you've ruled-out ignition timing, you may need to go back and remove any rough edges on the head.

 

[Jeff Pozorski]

Hi Manny,
You might have a week timing chain tensioner. With age they become weak and will rattle at high rpm's. My first Manta had the problem and it was very noticable only at the shift points. At lower rpm's it was silent. There is a fix listed on the classic-opels site which doesn't require removing the timing chain cover.
Good luck,
Jeff

 

[gtzero]

I didn't have much opportunity to experiment this morning. Only a couple of runs up to 5000rpm. The sound was much less than last night. I'll experiment more.

Scott,

The sound doesn't sound like detonation. Unfortunately, I'm familiar with that sound.

Jeff,

I'll check the timing chain tensioner possibility out.

Thanks,

Manny

 

[Jeff Pozorski]

Manny,
When you ran the car this morning I take it the engine was cold? As it warms us the timing chain will stretch ever so slightly which is why the tensioner is there. When cold the chain is tighter and will make less noise than when it is warmed up and stretched. Definately sounds like the tensioner needs replacing or repairing.
Jeff