tap !!

[Twiz]

hi,

Got a rally prepped 240Z which had a full engine rebuild a few months ago.

Ever since getting it back its had a tap, just like a loose tappit or rocker.

We have tried everything to try and track this down.

1. tightened all the rocker clearances down to 0 and briefly ran the engine, tap the same.

2. took front cover off and checked chain tensioner etc.

3. took pan off and checked big ends and mains etc.

4. ran engine with 1 spark plug out, one by one, cant detect tap from that.

5. When spinning engine with all spark plugs out there is no tap.

6. 'scoped through the plug holes to check all the valves are ok and not touching a piston.

7. the only thing we havent done is take out the pistons to check the wrist pin bearings but from the bottom with the big ends removed there is no discernable play.

One other thing, we have done 2 hill climbs and a rally cross including reving the engine over 7000 regularly with no change to the tap intensity at all. Any one got any ideas ????

Twiz

Edited April 19, 2010 by Twiz
spelling

[olzed]

If you raced it and it's no worse ,can't be too serious.Could it be side movement in one of the rockers-probably a long shot.In my experience,a higher pitched tapping is from the rockers.If you ran the engine with each spark plug out in turn,and the tap remains,I would doubt a wrist pin would be the noise.

[Zs-ondabrain]

maybe an exhaust leak? That causes a tap or pop sound and without plugs, there is no compression to make the sound?

Maybe?

[IdahoKidd]

I am with Dave on the exhaust leak. Does the tap increase rythym with RPMs? Change sound or pitch with a load? Can you isolate it to front or back of motor or top or bottom? Any chance it goes away when the clutch is depressed? Is it there from cold start? What do you know about the motor? Could be piston slap, wrist pin... could be lots of things. Are you running manual fuel pump? More information will lead to more speculation.

[Twiz]

tap happens from first cold start up and increases with revs, but no change in sound or pitch.

engine had full rebuild so no piston slap. and all bearings were replaced.

No change when clutch is depressed (just me thats depressed !!)

Used a stethascope all over and cant pin point the location.

car has electric pump and the mechanical one is all blanked off.

Will check on the exhaust but I dont think its that. the tap is too metalic to be a leak I think. I think its in the top end but cant think what it can be.

Keep trying guys, I need to do an event in it in a couple of weeks. !!

Edited April 19, 2010 by Twiz

[jackboxxx]

hi,

5. When spinning engine with all spark plugs out there is no tap.

Twiz

This is what has me wondering....the question is why? ( is there no tap with plugs out...) has one of the plug openings been sleeved (stripped and repaired) or anything remotely like that??? maybe im barking up the wrong tree...

[Twiz]

I had assumed it was because there was no back pressure acting against the various moving parts, the engine was spinning free.

the head is fine, nothing wrong with the plug threads

Edited April 20, 2010 by Twiz

[Gary in NJ]

I too would replace the exhaust gasket. At the very least, check for a loose nut on the studs.

[olzed]

Have you tried just removing each spark plug lead in turn so obviously when that cylinder isn't firing there is little load on it.If its a wrist pin the noise should decrease or stop.

[Oregon260z]

iam probaly wrong nothing new to me but when I worked as a motorcycle tech a guy brought in a bike complaining of a tapping sound that started after he had someone rebuild the motor.... took me about 2 mins to figure out that it was 1 spark plug was just a little bit longer and was tapping on top of the piston changed plug and problem went away.

[Twiz]

we found it !!! ( well actually my son found it) 1 lobe on the cam had a "dent" in it, not sure what caused it, probably a legacy of the dropped valve on Targa. Will have to check the oil distribution tube to make sure the hole opposite that lobe isnt blocked and also that the cam was properly hardened.

Any way the dent was causing a second clearance greater than the measured gap when that lobe was fully closed, hense the tap !!!

Amazing, after owning and racing Z's since they came out I never had or heard of that problem before.

Thanks for all the responses guys !!

If your interested you can see the car on www.rmtcontracting.com/rsport

Edited April 21, 2010 by Twiz