Engine noises

[digitech]

I have been having a blast driving the 79 Spider again, thanks to Jon Logan! So far, put about 300 miles on the rebuilt engine and after a few minor issues, things appear to be good. As you may recall, Jon found the head "done" by Paeco to be junk, found me another one, did the valve job, cleaned up the ports, installed the cams - original on exhaust, 40-80 on intake, and set the clearances. Paeco did the machine work on the block but I had it gone over again by a local shop and I assembled it. I've been running around town, breaking it in, building up some miles and confidence factor, top down, of course, every chance I get.

I have noticed a bit of what I think is valve train noise but I'm not sure. It's a little bit more noticeable with the top up but you can hear it top down as well. I can't hear anything much at idle, mostly only with a mechanics stethoscope and then it seems to come from exhaust valves #2 and #4 as well as intake #4.

However, this weekend, I checked the clearances on the exhaust side and all are around .017", so actually they are a little on the tight side instead of loose. Of course, I checked with the engine stone cold - several days sitting-in-the-garage-cold. So now I'm wondering where the noise is coming from, how best to isolate it and if I need to worry?

The car runs well, once it's up to operating temp. When it's cold, it's a bit noisy and stumbly - has a 34ADF on it - then smooths out as it warms up and idles at 900. Cranking compression is 155-160 on all cylinders, vacuum is fairly steady but a little on the low side at 16 - 17 - I put that down to the cam on the intake. Ignition timing is 10BTDC.

To me, the noise sounds a lot like spark knock as I hear it the most with the engine under load and on acceleration but varying the timing doesn't seem to really affect it nor does running 93 octane. Plus the pistons Paeco installed were supposed to be HC but only had 2mm dome to them - I doubt my compression is much over stock.

Anyone have any ideas or is this pretty much how these solid lifter engines sound?

[ventura ace]

What are the clearances for the intake valves, and what does the cam manufacturer recommend?

The 40-80 regrind that I use has clearances set at .011" or so, per the manufacturer recommendation. At standard cam clearances around .018", it wouldn't be hitting on the ramps for the cam lobe, and would probably be noisier.

Alvon

[majicwrench]

Have no idea what you have for pistons, but forged pistons can rock and knock a bit cold, when they heat they swell and quiet down if all is correct.
And a tiny exhaust leak can fool ya....
Keith

[manoa matt]

I had similar valve train noises when my cylinder head was rebuilt. Cams, valves, valve guides, and springs were all stock and within specifications so they were not changed. I also noticed the noise on the exhaust side, but it only occurred through a limited RPM range. If I held the rpms at 2300 it would make the noise but go away above and below. After about 500 miles the noise went away. The #4 exhaust shim is the hardest to change out due to a casting ridge around the distributor hole.

[digitech]

Jon set the valve clearances, original exhaust cam = .019 and the 40-80 Alquati = .016. I haven't checked the intake yet but after looking at the exhaust valve clearances, I'm not expecting to find one very far out; it's not like Jon doesn't know what he's doing. Soon as I get another chance, I'll be giving my exhaust bolts/nuts another look checking for leaks and I'll rack up some more mileage. I plan on changing the oil around 500 miles and I've been told to try 15w-40w for the winter and 20w-50w for the summer. Thanks for the help!

[digitech]

Also, all I can tell you about the pistons is they are used Venoli brand????? Don't know where Paeco got them from but they waited and waited for them....or so they told me.

[BEEK]

venolia, makes great pistons, they make them to spec though, so you would have to know what was ordered.
10491 1800-2000 thats the venolia blank part #

[digitech]

So, do you know if they are forged? I never thought to look for a part no. before I installed them so I can't say what they gave me.

[manoa matt]

"Plus the pistons Paeco installed were supposed to be HC but only had 2mm dome to them - I doubt my compression is much over stock."

If the pistons were used, and machine work was done to the block then I would guess the pistons are oversize and the block was bored to suit. When the block is bored out you increase the swept volume, but the compressed volume stays the same. In essence you increase the compression ratio. So even with 2mm domes it can still have a higher than stock compression ratio.

I have a set of Mahle pistons that are 84.6mm with small domes around 2-3mm and they are reported to yield 10:1 compression.

[131]

I have a set of Mahle pistons that are 84.6mm with small domes around 2-3mm and they are reported to yield 10:1 compression.

I've recently had a block bored and decked to fit a set of 84.6mm 1800 pistons with a 2mm dome. With an 1800 head fitted, and crunching the numbers, I come up with 10.5:1 static compression ratio.

[digitech]

My block has been bored to 84.4 so my compression MIGHT be higher than I thought, although, I would have thought the cranking comp numbers would have been higher. Anyway, at this point, it would be impossible to say as nothing was measured (to calc.compression).

[manoa matt]

Mick, if you got a 2L block with an 1.8L head, then yes 10.5:1, but if you have a 2L block and a 2L head then it will be 10:1, however the other variables to consider are: the compression height of the pistons themselves, and how much your block and head were shaved.