Bought a 351 Cleveland.....no biggie people do it all the time. Did a rebuild, (replaced everything brand new) ran ok but a little stiff for the street. Decided to install a mild hydraulic cam, lifters, push rods, springs and new rocker arms. All items were for a stock 351 except the hydraulic cam was a step up from a stock cam. Had the heads completely reconditioned. Re assembled with the new parts & reconditioned heads. Have done this many times with out a problem. Well could not get it to start. Did the normal checks, getting gas, timing ok, spark ok, but every time I turned it over it just didn't sound right. Took a compression check and no compression across all cylinders. Hummmmmmmm. My thought is the valve job was messed up and the valves are not closing, I am going to do a valve check with a dial indicator just to check valve movement. Any suggestions before I tear it down?
I'm assuming you've checked the valve adjustment already to ensure proper lash settings? Or are these rocker arms a non-adjustable bolt-on type deal? It is unlikely a bad valve job would result in TOTAL loss of compression across all cylinders. Something like drastically incorrect pushrod length or rocker arms that are cinched way down could cause the valves to stay open all the time.
If the heads have been milled too much this can happen,had a head done on a GM 2.5 4 cylinder and that happened. The rocker arms on the 2.5 were a positive stop set up similar to a Ford and with the head milled too much all the valves opened enough to where there was no compression,on that motor I had to put shims under the rocker arms to get it to run but you might have to change the studs to go full adjustable. Loosen the rocker arms and see if it will run.
Be sure you have the firing order correct. The new cam may have the newer firing order. Do the research. Hope this helps
You need a tool called a "push rod length checker" they run about $15 from Jeg's. Then you can order the correct length push rods,you have probably bottomed out the lifters so zero compression is the result.
To check the valve seat to head seat interface, pour a little trans. fluid down the ports, both intake and exhaust. If there's a good seal, the fluid won't leak past the seats. Mike
Was the person who did your valves aware that this was a non-adjudtable valvetrain &that the stem heights needed to be set ?? dave
The The head guy just did a valve grind, knurled the guides, installed the valves, seals, springs, keepers and set to correct height (he said). I did get new rocker arms which may have had a different ratio than the stock rocker, but don't think that would have an effect a drastic effect on the valves opening & closing would it ?????
Yes I explained everything to the head builder. He was an experienced guy been in the same location for 40 yrs. Seemed pretty knowledgeable and understood valve height and set up. Claims he followed the Comp Cams recommendations on valve height & set up technical stuff.
did you tell head rebuilder which ratio rockers you put on when asking him why no compression.also were rockers the proper ones for your engine? (meaning pedestal mount)
Before you tear it down.........do a leakdown test. First, do it with the rockers on. Make sure the valves are both closed on each individual cylinder when you do the leakdown. If you have excessive leakage (more than 10%) remove the rockers or at least loosen them until you're sure the rockers are not putting any pressure on the valves and do the leakdown test again. If the leakage is less with the rockers loose, then you will know where to start....to cure the problem. Hopefully you can find the problem without a teardown. Good luck! A dual gauge leakdown tester is a really handy tool and not that expensive.
Did he set valve height or spring height? My guess is spring height. Once you get to messing with different cams, rebuilt heads (valve job sinks valve deeper in head) different lifters, etc, you need to get the heads set up for adjustable rockers and guide plates. What rockers did you put on it? Are you 100% sure they are 351C rockers? SPark
Unfortunately those non-adjustable type rockers typically work best when you have damn near stock valvetrain geometry. Factories use them because they are pretty foolproof for stock applications, and they clearly save time and money not messing around with one more adjustment. This all goes to shit when you start milling heads and decks, making minor changes to valve or pushrod lengths, dealing with varying rocker ratios, etc... The hydraulic lifters are somewhat forgiving, but at some point you either have to shim the rockers to accommodate the changes, or switch over to the fully adjustable style. Even completely stock rebuilds often require shimming to make up for discrepancies. Still, it's probably not the rockers alone that are the problem. My best guess is still incorrect pushrod length, but it sounds like you're on the right track with that already.
what rocker arms did you use i have done lots of 351c with preformance cams and full machine work with no big issues first thing i would do is check the lash roll it to topdead compression on a cylinder loose the rockers slowly tighten the rockers till the push rod has no up and down clearance when ya get there see how much of a turn it takes to snug the rocker arm to the head should be about 3/4 of a turn or so the valves being held open is the only thing that would cause no compression on all my 351c had the larges hyd bracket master lunati made in it with stock rockers with no shims and stock rockers
The Jalopy Journal
