924Board.org

[Mclaren924]

Have a customer at a friends shop who I just rebuilt and installed a new engine for their 77 martini car. Motor was completely redone, new bearings, rings, hone on block, deck both surfaces, guides, seats, grind valve faces, yada yada yada. Long story short is I finally got it to fire up today and notice there is a horrible ticking/rattling noise that seems too fast to be crank related, it seems to be coming from the lower part of the head and sounds like it shares a similar rpm to the camshaft. It's not there at all on cold start but gets louder as it warms up and can be heard at higher rpm even when cold . Does not sound like piston or rod knock to me and sounds like it may be happening on back two cylinders the worst but truthfully could be all 4 as its pretty damn loud.

I have pulled the cam and followers out today after trying to shim the noise away in the lash adjustment and no dice. The cam looks in great shape but looks don't measure runout so will check that tomorrow. The buckets on the other hand look like they have seen better days. Noticeable rough patch on all 8 and there's a few at the very edge of the wear limit diameter wise. Have begun to ponder if these are the culprit but am not convinced, the follower bores in the head look great.

The machine shop assembled the head and I'm beginning to wonder if something is not quite right, they did put the cam pulley on backwards and completely jacked up the valve lash on all 8 buckets when I got it back.

Looking for you guys who have been writing posts on here for as long as I have been alive (02) and have heard this noise before and can save me some anguish. Current plan is to take over a clean set of used buckets and reinstall the cam and buckets and shim them and hope that fixes it. Really get a bad feeling the head may have to come off to resolve this though





Video with sound

https://imgur.com/ZmgemH3
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1980 931 "Salt" Bucket wannabe racer (not started)
1979 924 Sebring "Pepper" -Sold
1980 924 "Donnie" (Parts car)-DEAD
1977 924 Slicktop "Pennie" Bucket turned Silver Spoon

[Cedric]

When you say shimming do you mean adjusting the screw, or are these after market ones?

Theres lots of talk about using used ones, but ive done it and it have worked well for years. They are very cheap to its nice to just buy a bag and have on hand if something ever happens. The adjusting screws might have to be changed around though to get the correct clearance and position of the screw, there are several sizes, maybe you should double check that none of the adjuster screws are to far into the bore and are getting loose.
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1980 924 Turbo
www.instagram.com/garagecedric/

[924RACR]

It shouldn't be remotely possible on such an early engine, but any chance of pistons hitting valves? Maybe a quick borescope check for contact on the pistons to rule that out?
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[safe]

camshaft turns at half the speed of the crank. Sounds more like something touching/rubbing externally.
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/Magnus, Stockholm Sweden
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Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe

[Raize]

Mine does that too, I thought they all did that.

[Mclaren924]

Thank you for the correction about crankshaft and camshaft rpm reaction safe, I did think maybe there was something cashing this rattling noise externally but sadly after warming motor up it gets significantly worse. Decided to pull the head off and see what was going on and I truthfully am not sure if I found the smoking gun or not. Cam and buckets and springs all looked good to me and the buckets/cam measured within spec for lobe size and bucket diameter. The springs were put in the correct orientation and nothing erroneous was found in the spring/top hat washer thing. The valves and valve guide seats ade what I believe to be causing this noise. The machine shop supposedly put in new guides, after messing with the valves loosely with no spring, I determined there was a large amount or rocking play between guide and valve when the valve stem was flush with the top of the guide. I grabbed a used nasty parts head and tried the same valves from the machines head in the nasty head and they had basically no play at all, any movement resulted in the whole head rocking. Took the nasty valves over to the “new” head and they had the exact same rock as other valves. Got out the dial indicator and found about .300 of play on every valve in my newly machined head. I’m theorizing that this play caused the valve to seat at an angle momentarily and then slap the other side of the face shut creating the ticking noise I’m hearing. The only other valve issue I found was one valve had about .007 runout when checking its straightness while the rest were around .0015 and it had a pretty fat lip on where the face was cut and runs into the face/stem area . I don’t think could have caused that much ruckus but it’s probably an issue. Other than that the head checked out in every metric I could check without more equipment, I am concerned about how good and if they even did the valve guides considering they are like .02 off wear limit and subsequently how well the seat was machined with these worn guides. Thanks as always guys!
_________________
1980 931 "Salt" Bucket wannabe racer (not started)
1979 924 Sebring "Pepper" -Sold
1980 924 "Donnie" (Parts car)-DEAD
1977 924 Slicktop "Pennie" Bucket turned Silver Spoon