I suspect the hollow cast ali fan housing bolted directly to the block amplifies any engine noises like a speaker.
Thanks for the advice @Zed ; will have a play around with the tappets again in the way you suggest. The noisy tappets are distinctly clacky rather than clunksome. Not sure why they only really resonate at idle, but has been on my list of suspects all along! I went to the 914 half-century celebration at Brooklands back in 2020 where they amassed 50+ cars - never heard so many bags of spanners in place at the same time!!
Interestingly, VW Engine Co recommended that I set up the valves by getting max lift on each valve and setting the gap on the valve on the other side of the cam. For instance when no 3 exhaust is fully open on the cam lobe, no. 1 exhaust is ready to adjust. I went round marking these up and magically they are all at either 90 degrees before or 90 degrees after TDC on the intake stroke. So I now have a pulley marked out in 90 degree increments and can rotate an engine round 720 degrees checking the gaps by both methods. The conventional method will see the gaps set at 45 degrees off the centre of the base circle, but it doesn't seem to make a scrap of difference. Not with a new cam anyway.
And I had mine blasted inside to clean all the grease off. It was probably helping to damp down the sound.
Good work! Rather you than me! I had a friend who bought a worn out cam grinding machine he intended to fix. You have to wonder how many cams it ground in that worn out state, it didn't wear out overnight. Those machines are costly to buy and costly to fix even for a company that grind a lot of cams and I wonder how many of our suppliers are using worn tooling because of that - you know - I'll just do another thousand THEN I'll fix it. Me too! Doh! Maybe a noisy exhaust would help.
Right - so, have been doing some diagnostics (but no smoking gun has been found...); With @Chrisd we rigged up pressure and RPM gauges and ran up the revs yesterday. Unfortunately the engine doesn't like idling when the air filter is off, so we didn't gather much data of when the actual retched idle noise is happening, but I think we got enough to draw some conclusions. Here's the video; ..And here's a graph of RPM and oil pressure versus time noted from the video footage; Remembering this is a single relief valve engine, I think it shows the oil pressure control valve is working as it should and is capping the pressure at about 62-64 psi. So not much point in swapping the control piston out for the old one. The other thing we did was a leak-down test on each cylinder (I seem to have lost the adapter for the compression gauge!); this showed that cylinders 3 and 4 were about 17% and 1 and 2 were 9% pressure drop, so again I think I we can say the rings and valves are sealing as they should. Any thoughts welcome! Next is to look at the valve settings and do some experimentation on the particularly clacky ones....
What's the exhaust like? This might seem daft but I have a few pinholes and I recently tacked some metal over a 1 x 3 cm hole. After a bit of Gun Gum the exhaust is a bit quieter and so is the clack.
Nothing is daft in this game. I’d say the exhaust is ok - it is about 30,000 miles/12 years old, but it’s solid and I didn’t see any holes when I had it off. I’ll take another look though.
If you have hx/head leak, it's pretty clacky on an oval port head, which most are. This is a head/exhaust leak on mine.
Oooh - that’s exactly what it sounds like. Good work! Something else to check out tomorrow if it doesn’t rain and the whoever parked blocking the drive b*ggers off…
It was driving me nuts. A phone is a handy tool for listening while it looks where you're listening but as you probably know a simple piece of garden hose is the best way to home in on an exhaust leak, when you get it close to the leak it's very obvious, but close you must be. You may/may not be able to get the end near enough to the head/hx joint without removing the lower tin. head/hx leaks in particular do sound metallic IME, but I'm always happier to find them then something that is actually metallic obviously!
Well, if being being driven nuts is a symptom then it’s definitely the same thing. I did check the the hx\head of course, but perhaps not as methodically as I should have. I’ve been using a cheapo stethoscope, it’s amazing how sound is altered using it - it’s very difficult to work out what you’re listening to. I’ll see if I can get up on the lift tomorrow and check it out properly. Many thanks for the pointer…
Thank you for holding...... Well, I've been all over the exhaust/HExs with various listening pipes but can't detect any puffing noises from anywhere other than the exhaust exit. I re-torqued up the Hex/head nuts, and a couple gave a quarter turn, but made difference to the rogue engine noise. So, next on the list is to revisit the valves, bearing in mind what @Zed said; So I re-checked the valve gaps - they were all 0.15mm except No3 inlet which was a little loose at 0.18mm. Here's what I found when I looked at the adjacent cylinders; At No1 TDC 2 inlet gap is 0.23mmObservation - normal 4 exhaust gap is 0.20mmObservation - quiet At No2 TDC 3 inlet is gap 0.30mmObservation - noisy 1 exhaust gap is 0.20mmObservation - little noisy At No3 TDC 4 inlet gap is 0.20mmObservation - quiet 2 exhaust gap is 0.18mmObservation - quiet At No4 TDC 1 inlet is gap 0.30mmObservation - noisy 3 exhaust gap is 0.20mmObservation - fairly clunky The observations are from me waggling the rocker by hand. So - my first instinct is not to be very happy with the quality of the Mechanical Camshaft 1700-2000cc Standard bought from you-know-who and to kick myself for not checking it properly during the rebuild. Perhaps this is why as @andyv says "Interestingly, VW Engine Co recommended that I set up the valves by getting max lift on each valve and setting the gap on the valve on the other side of the cam. For instance when no 3 exhaust is fully open on the cam lobe, no. 1 exhaust is ready to adjust". Perhaps they use the same off-beat cams. I think I'll give VW Engine Co procedure a go tomorrow and see it makes any difference to the errant engine noise. As ever, thoughts welcome.
I'll be interested in your findings. Note that you should check whether the maximum lift occurs at +/- 90 degrees to TDC in your case. I wasn't expecting this as there's valve overlap at the ends of the piston stroke, and inlet and exhaust valves usually have different characteristics. It depends on the cam profile. It's tricky observing the valve lift and also turning the engine. I used an endoscope for this so I could see round the corner.
My brain is having a day off, but if say you set the gaps to be correct following the engine co advice, is there a risk that they wouldn't be closed properly when they should be? The cam sounds like poo from your measuring, but maybe it doesn't effect the running and actually doesn't really matter. I'd still be inclined to set each cylinder at TDC because whatever the shape of the cam that's the point where it matters. Watching with interest.
This is the stock cam at the end of the exhaust stroke with the exhaust closing and the inlet opening. I should have done the firing stroke too as that would have been more interesting... or maybe not.
