Inliners International Forums General Discussion Engines 250 Engine Sound Help

Link to a video with the sound here

Hey guys. Been a very long time since I've posted on this board but I finally got my car painted and reassembled earlier this year with my turbo chevy 250 setup. It runs great but it has been so long since I've heard it run that I forget if certain noises were always there or if this is something new.

The engine has .040" over forged pistons (piston slap?), roller rockers (valve train noise?), flat tappet turbo cam, Holley super sniper EFI (injector noise?), a SPA turbo manifold (exhaust leak?).

There seems to be a sound coming from the rear of the engine in maybe cylinder 5/6 that seems to be more pronounced on the passenger side. It's between a tick and a knock and seems to not be present at RPM/cruise/power. You can really only hear it at idle and it seems to fade in an out. The engine runs great and has plenty of oil pressure. I've reset the preload on the hydraulic lifters like 5 times but it never seemed to help so not sure if it's valve train related.

I was fairly confident it would be piston slap but I seem to only be able to hear it when the engine is hot whereas piston slap would be most pronounced when cold and slowly get better.

I've had a boroscope in the cylinders and there is no visible damage to the walls or piston heads. Plugs look great.

Timing is 15* at idle.

Curious if y'all have any thoughts or maybe 250s just sound like this and I'm misremembering.

Snowman, It is good to see you back here and to know you are still working on the turbo setup. As you can see this is not the same site it was when you started this project.

I have little to offer on the noise. If all was well when you last ran it and nothing was changed then my first guess would be a lifter that was compressed during the time it sat. (hydraulic lifters?) Adjusting may not fix it if the spring had weakened or there is a score or spot in the lifter bore. It might be able to pump up at higher rpm? I chased a a lifter/rocker noise on my 270 for a few years. It went away when I changed headers. ???

Hey beater!

Yeah a decade can sure change some stuff!

Yeah the thing was I broke it in without an exhaust, drove it with only a downpipe for a bit, and then put an exhaust and muffler on last summer. I�m not sure if it was always there or if I only heard it after I put the exhaust on.

Are you saying that it went away after changing headers meaning it was probably an exhaust leak?

The other thing I remember thinking last summer was that because the sound seems to come in and out like 2-3 taps and then silence and then 2-4 taps, it might be a slightly bent pushrod? The channels between the pushrods and head are pretty darn close and I did see a tiny bit of wear on the coating by the head on the pushrod when I was resetting the preload in the hydraulic lifters. Maybe the play in the roller rockers makes a pronounced tap as the pushrods are rotating around? Just a thought I suppose. It�s the only thing I can think of that would oscillate in that pattern.

It has about 1200mi on it so if it was catastrophic, I assumed it would get worse or have smoked the motor by now. There was no glitter in the oil filter with the break in oil either

Appreciate the input!

Wondering if it could be the pushrods rubbing in head, easy to check. They will rub right where they come out of pushrod hole in head.
Second thing coming to mind, possible cam bearing failure? You might be able to insert the bore scope into fuel pump hole to look at the center 2 cam bearings.
How is the oil pressure? Especially at idle.

I'm thinking the noise was always there and you couldn't hear to until the muffler was added. I'd check out what Tom suggested about the pushrod clearance. Did you add pushrod guides with the roller rockers?

Tom are you saying to pull the cam to look at the bearings?

No It wasn't an exhaust leak. It was something the exhaust was doing with to tube header and the cast header quieted it. It ran better with the tube setup, Old Viper header.

If the timing wasn't heated before installing it could have walked off the end of the cam?? But i would check everything Else before jumping to this.

Hey Tom and Twisted! Great to hear from y'all!

I realized I made a whole video on this last year before I took everything apart for paint. There's a really great explanation and overview of my thoughts, showing the valve train running, looking at the pushrods out of the head, etc. in this video if y'all care to hear me chat for 10m

The link goes straight to the best example I have for that sound.

@Tom - The pushrods definitely seems to make a bit of contact with the head but it seems like it wouldn't make this kind of sound. You can see the bit of wear on the sides of the pushrods in the video at 4:21 in the video

I didn't think it would be a bearing failure because I figured I would've seen shiny stuff in my oil at my oil change in the beginning of the summer. Oil pressure is 15-20psi at idle. 40-45psi at higher RPM. No drop in pressure over time as these are the same pressures I had since break-in last year.

@Beater - I did not add pushrod guides with the roller rockers.

@Twisted6 - I had a shop do it so I guess I just assumed they heated the timing set to install it

I figured it if was a timing gear or camshaft related, I'd hear some scary sounds coming from the back and front of the engine from the thrust of the cam and have oil pressure issues but maybe not?

Many Shops do not know this, and they just press the gears on. You could pull the distributor and take a good look at the gear for any Odd wear on it.

Did you figure it out yet?

@Twisted6
Well I suppose I'll cross my fingers then :-/

@Beater
I have not unfortunately. I've doing other restoration and have had it parked and covered in plastic for a few weeks. I'm fairly confident it's the pushrods especially since they don't have pushrod guides as there's nothing else that would explain the oscillating. Next time I have the motor out or have another opportunity for some other work, I'll check the things y'all have mentioned. I don't think it's bad or concerning enough to justify a full teardown at the moment but I'll keep an eye on it.

I appreciate the feedback y'all

Don't forget about the old guys here that probably steered you wrong in the first place! It is good to know you still have the car and are still tinkering with it. Keep us up on what you ate doing.

I would never! Y'all have been invaluable and given me a love for these engines and what they can do. Y'all have been instrumental in the whole build and I'll never forget about inliners as long as I live.

Y'all didn't steer me wrong anywhere! My first complete engine build has lasted at least 1000 miles and makes more power than I ever could've hoped for!

I just got done painting the trunk so I'll try and get a video up and make a final post on my snowman4839 turbo build thread to bring that 15 year saga to a close. I'll go over everything that has been done, all the parts and little things, and try and get a driving video in there too.

Really appreciate everything y'all have done for me

Looking forward to the update. Hearing from you has brought some life back to the site, thanks. In all these years I never finished my MegaSquirt turbo GM throttle body 292 project. I just got so confused I put all in box and don't even know where it is. Life has its own plan.

Just posted the update here if y'all are interested. Made a whole video and showed it driving and everything https://www.inliners.org/ubbthreads...ds=snowman4839&Search=true#Post94719

I totally get it! Sometimes projects just get shelved for a bit. I kinda felt like that with the 250 turbo project and always felt horrible whenever I thought about it, but I started making cardboard lists of little things to get done and would spend weekends here and over the past couple of years and it just took putting one foot in front of the other to get it over the finish line.

Very Cool! Thanks for the update and enjoy this thing. Keep us up on anything new or fun.