If the adjustment is loose you should have clatter at low rpm also. weak springs and floating valves? Does your rpm stop increasing when you get the noise?

 

No noise below 3500 but immediately above that level. As soon as I hear it I back off the throttle because that clatter can't be a sign of anything good for the engine.

 

Some of the Ford engines of that era have press in rocker studs while others have screw in studs, Occasionally the press in studs start to pull out of the head increasing valve lash. The OP is silent on what specific engine and what generation of that engine is in his/her car. If a Ford small block V8, get Mannel's book for an encyclopedic look at all the variations that engine has experienced over it's many years of production. Consider also that your engine might be a mish mash of parts from several engines making it more difficult to know what you actually have.

 

To my recollection, the only 2 Mustang engines made with solid lifters were the 170 inline six and the 289 HiPo. If you don't have either of these, and the valvetrain is otherwise quiet, I'd inspect the parts for wear first, readjust to spec second and, if the noise still persists I'd drop the pan to inspect the oil pump pickup strainer for sludge and the main & rod bearings for wear.

 

To my recollection, the only 2 Mustang engines made with solid lifters were the 170 inline six and the 289 HiPo.

Hmmm… I think you can add the BOSS 302, BOSS 351, 351HO, 428SuperCobraJet, BOSS 429, and 429SuperCobraJet.

 

Mechanic's stethoscope is your friend to isolate exactly where the noise is coming from. Once you get used to the ticks, you can even pinpoint which cylinder has a sticky lifter/rocker. Harbor Freight carries them for a couple bucks, or you can use a long handled screwdriver held to your ear and move around the engine block.

 

sure its not just spark knock?

 

I also thought possibly spark knock but I think that would occur more often accelerating from low rpms

 

Sorry. In the process of editing I got rid of the sentence saying it's a 200 ci six cyl.
It's not the original engine and I think it was rebuilt at some point because it doesn't burn a drop or leak at all. Runs very well except for this issue.
No ignition ping on acceleration.

 

Have you tried using a lead additive in your gas? If the motor was never changed to hardened seats, it could cause a similar issue based on some reading I just did.

 

Assuming you have a tach installed and this is how you know it starts at 3500. My first thought is to check your oil level, next, pull VC and following a prescribed method for adjusting your lifter pre-load. You don't mention your experience level, "pre-load" is the term used relating to adjusting hydraulic lifters. If you can determine ,for a fact, through invoices or engine build history the lifters are solid, then, check the valve lash. Perhaps, someone here knows for sure, given your engine was a "stock" rebuild. I agree with Woodchuck on pulling the pan and check the oil pump screen. It could very well be a plugged screen and the engine, at those RPMs, is starving for oil. You state that it must have been rebuilt, but, you have no indication. It could be it's never beed apart?

 

Kenash...
Yes, I know 3500 because I installed a tach. Oil is fresh (I do it myself) and the level is good
My original engine went bad beyond reasonable repair and I was basically given this one. I don't have any paperwork but it sure seems tight, doesn't leak a drop, and runs well...right up to 3500 rpm. Could very well have never been opened.
I used to do my own work, but we moved out to 3 acres in the woods of OR where my small "garage" has a dirt floor. However, a mechanic friend has gray hair, tons of experience, and I trust him completely.
I just figured if it was top end and could be done by removing the VC I'd do it myself.

 

Then go with plan "B". That is, pull the VC, perform an inspection of the valve train. Unless modified in its past, most likely you have a non-adjustable valve train, in which case, you would have to change the PRs to reduce any play. Sounds dramatic, but, you won't know until you pull the VC.. Sorry, someone with more intimate knowledge of your 6 banger will chime in. In the meantime, you might research the date code of your engine to determine it's year, since you state it was given to you.
You don't mention what year mustang you have? Very important to get better advice.

 

As a microwave technical engineer once said to me, something is not right somewhere. I thought it was rather profound, LOL.

I'm with the oil pressure people for checking first. If your oil pressure is running low you will notice it more as the rpms go up and the oil pressure doesn't come up enough relative to the rpms. It can be as low as 10 psi at idle and you likely won't hear any valve train noise.

It does help to know if you have solid or hydraulic lifters before you go adjusting on them. It could also be worn parts in the rocker shaft assembly making it run too loose. If it is in the rocker shaft I would expect it to get louder as you rpm up.

I've run solids for a long time in my hot rod and it doesn't exactly rattle at higher rpm. It is more of a meshing sort or noise or a shssssssshhhing noise sort of like a loud engine white noise. Even with a minimal street exhaust though my engine is fairly loud so that may be muffling some of the lifter noise.