Hi all,

I've got a problem that I hope someone can solve as lots of local people here are not sure what to suggest.

I've recently put a 1989 305 TPI engine in my car. It has several modifications including head work (porting and larger intake valve), plenum porting, 24lb injectors and a custom cam shaft. And the engine runs like crap.

At first I had bad lifters and we replaced these. The new lifters behave very well, and upon installing them and reassembling the engine, we started it. The engine ran beautifully with a steady 20 inches of vacuum. However as the lifters filled with oil with the engine running it started to run like crap with engine vacuum bouncing between 0 and 10inches. Even so, we set the rockers with the engine running and it made no improvement.

I did a compression check and I got a variety of wild readings, some cylinders reporting 0psi. I undid the rocker nuts all by one turn and did another compression test - all cylinders gave me 160psi on the third crank.

It seems that the valves are floating and the only thing we can conclude is that the oil pressure is too high or the springs are too weak. I know the guy who did the heads on my engine and he's a well known professional at his job. I'm using the factory oil pump and have blocked off the oil filter bypass so that all oil must go through the filter. It can't be an oil gallery blockage because the heads are being oiled up top as normal.

Has anyone seen this problem before or can suggest a fix for it? It's been suggested to me that I put 10W-30 in the engine in order to lower the oil pressure. I get about 40-45psi at idle.

Any thoughts are much appreciated!

Cheers,

 

I don't think this has anything to do with your oil pressure being too high. What oil weight are you using now? 10w30 is probably best anyway, but besides the point.

This sounds like you had tightened your rockers too much before. I don't think it's even possible to get valve float at idle, and whatnot. Since you loosened the rockers, does it run now?

What's the cam lift? Did you machine the heads for more lift?
What springs are on the heads?

 

I'm not sure on the oil weight now, but it's Pennzoil racing oil. 25w-50 or something, I can't remember.

Since putting in the new lifters, I haven't run the engine with loosened rockers. I do remember running the engine with the old lifters and the rockers loosened and it ran, but the valvetrain was quite noisy.

Cam lift is .487 and I'm using the factory 1.5 ratio rockers. I don't recall the heads ever being machined for more lift, but 18 thou was taken off the block deck. With my dished pistons, this was to get a true 9.5:1 compression ratio on 91 octane fuel.

 

sounds like the valves are too tight, redo them with the engine not running.

 

Exactly. Do the EOIC method, and use a feeler gauge between the positive valve seals (if used) and retainer, just to make sure you're not getting any interference. If you ran it with lifters over-tight, it may have whacked it a few times.

What valve springs? I'm hoping aftermarket?

Yea, once that oil is used up, i'd say go to a 10w-30. It's not a race car, it doesn't need race oil, that's wayyy to thick for me.

 

If the valves are floating with the engine at idle or low rpm, you should be able to push open a valve with a finger and very little pressure.

Sounds like you misadjusted the valves.

Hydraulic lifters have a wide tolerance for adjustment but should be as close to proper adjustment as possible.

There are lots of threads on what valves to adjust when. Using the TDC mark you can adjust all the valves by lining up the TDC mark on the balancer twice.

As for adjusting a hydraulic lifter, with the engine off, back off the adjustment nut. Allow the lifter piston to expand. 10-30 seconds should be fine. Now tighten down the adjuster nut just enough until you can't jiggle the pushrod. The valve is now adjusted to zero lash. The lifter now needs a preload. Tighten the adjuster nut 1/2 turn more. This sets a 0.030" preload in the lifter. Don't worry about being able to spin the pushrod after that. That's just the way a hydraulic lifter works. If you overtighten the adjuster nut, you remove all the oil from the lifter. This can cause the valve to stay open when the lifter is off the cam lobe.

 

Thanks for the hints guys.

Yes, the they are after market springs. I've bought some replacement 10w-30 Valvoline oil so I'll put that in and readjust the rockers by hand and do another compression test.

Could you please explain the process of using the feeler gauge? What sort of clearance should I be getting?

 

he is saying use the feeler guages to check for retainer to seal clearence.

when doing the valves tighten to zero lash then 1/2 turn more.

not sure of the clearences, but if you have a lot then it's not a problem, only if you have too little is it a problem.

 

Exactly.
While you're redoing doing up the lash, anytime you notice a rocker at it's max travel, just peek under and see if you've got some clearance between the seal and retainer. If you've run the lifters highly tightened, you may have taken up all the slack you had, and crushed the seal, bent a retainer, etc. Just eyeball everything, make sure nothing is "funny" looking.

 

How much lift is on the cam? What rockers are you using?

Excessive lift can cause the bottom of the spring retainer to hit the top of the valve seal. Stamped steel rockers only have a slot long enough for just so much lift. If lift is excessive, the slot in the rocker will hit the rocker stud before the cam is at max lift.

There's so much to know about using non factory parts that it's so easy to install the wrong parts and not know what's wrong.

At max cam lift, check the distance between the valve spring coils. You should have at least 0.060" between the coils.

 

In order to check the retainer to seal clearance, I'm going to have to take a spring off to be able to measure aren't I?

The lift is .487 and I'm using the factory 1.5 rockers.

I haven't checked the distance between coils yet, I'll do this tonight. I presume I take the measurement when the valve is fully open?

I changed the oil to a Valvoline 10w-30 and lashed all the valves and then did a compression test. Now, unless I made a dog's breakfast out of lashing them (and I feel sure I didn't), cylinders 3 and 4 are giving me no compression at all, yet all the others are giving me consistent compression of about 150psi. I haven't started the engine at all, I'm just cranking the engine over without starting to do the compression test.

What do I do next?

 

Recheck the valve adjustments on those 2 cylinders first since that's the easiest thing to do. Make sure both valves are closed before adjusting. Shortly after the intake valve closes, the piston will be coming up to TDC on the compression stroke. If the adjustment is good...

Modify your compression tester so that you can put compressed air into the cylinder. Loosen off the rockers for those 2 cylinders and use an air compressor to fill the cylinders with air. Listen for leaks. If a valve isn't closed (rockers are backed right off or removed) you'll hear air coming out the carb or tailpipe. A valve not closing usually means it's bent. pull the heads and have them checked.

If a lot of air is going into the crankcase past the piston, you've got bad rings or a hole in the piston.

 

OK, I'll do that when I go home from work later today. It's been suggested to me recently that I ought to have the engine running when doing these two cylinders to bring the oil pressure up to ensure the lifter plunger is sitting up. Sound like a good idea?

Ooo gee, I hope I don't have this problem. Come to think of it, I doubt I will have. Reason being that when I backed all the rockers off I got 160psi in every cylinder, including the now suspect 3 & 4 cylinders. I mentioned this in the fourth paragraph of my original posting. I haven't started the engine since doing that successful 160psi test, so I doubt from just engine cranking I will have damaged a piston or valve. Touch wood.

 

You shouldn't have to start the engine to "pump up" the lifters. The spring inside the lifter will easily push the piston to the top of the lifter allowing for proper adjustment. Sounds like they're still out af adjustment. Worse case is that you have a couple of collapsed lifters and when you adjusted them to the lifter preload, they were already bottomed out and now won't left the valves close.

 

This thing is driving me nuts. Here's what I've been doing recently...

I backed off all the rocker nuts. Then I made up a piece of paper tape and marked it exactly into quarters and wrapped it around the harmonic balancer. I figured this would be a more scientific way of determining when rockers where rocking.

I set all rockers to 0 lash and I shone a powerful torch into the heads to inspect the plunger inside each lifter before and after I set the lash to confirm that nothing odd was going on. All of the plungers looked fine and were at the top.

A compression test gave me about 180psi in all cylinders. I reassembled the engine, started it and it ran nicely. Naturally the valve train was rather noisy from the rockers, but the engine was happy and it gave me a steady 22inches of vacuum although idled high at about 900RPM.

Then I shut off the engine and gave each rocker nut quarter of a turn, put engine back together and fired it up. I then got 20 inches of vacuum and the engine seemed slightly less happy although the valve train was much quieter, but still not silent.

I took the car for a good drive last night and today decided to do another compression test and the numbers varied...

#1 175psi
#2 172psi
#3 120psi 120psi 100psi
#4 150psi 120psi 150psi
#5 170psi
#6 170psi
#7 162psi
#8 160psi

You'll notice I wrote extra readings beside #3 and #4. I decided to test these cylinders again and I got different values. I don't understand how this can happen??

For fun I took the springs off cylinder 3 and got them tested. At an install heigh of 1.7" they have 110ln of pressure, at 1.2" it's 310lb pressure. Both valves move freely up and down so I don't see a problem there.

Help please, this is engine really is rubbing me the wrong way!

 

Put a dial indicator on the rockers and check how much lift is on those cam lobes.

As I mentioned above, also do a leakdown test. A compression test alone won't tell you as much.

 

I found out the answer to my problem.

Since I was having trouble around cylinder 3 and 4, I took off the rocker on exhaust for #3. I attached a DTI to the end of the pushrod and made up a paper tape to go around the harmonic balancer, marked off in 10 degree increments. I took lift readings and plotted a graph and noticed that at the end of the lift cycle the cam was bottoming out by up to 0.012".

I took the cam out and had it checked professionally, and it's been determined that the cam is bent. Hopefully by getting it straightened it will remove the bottoming out problem.

 

don't put the stocker back in! you've got the perfect opportunity to pu t a decent aftermarket one in.

edit: i see you already have an aftermarket cam, my bad.