Hi guys! what a privilege to have this gr8 forum and members. So ive put a a couple of chevys together and never had an issue. I tore a marine 350 apart 4 months back, had it on the stand for quite some time deciding what to do.. Micd up the bores and they werent tooo bad (max was 7 thou clearance) and for a old banger i didnt care - ive seen motors run ok with some extra wear. Anyway - before i tore it down the compression numbers were good - 125 to 145 on all 8.. put in new gaskets.. honed it and threw the old rings in - it still had the original double roller from GM. So I ran it on the stand little and dropped it in the boat. Not sure how or what but it just ran awfully! Having said that i did manage to get 18" vac on the manifold, with the needle jumping around a bit an inch or so. These are smog heads with flat tops and a double roller GM timing setup.. All bearings were good and nothing tight. I tested a different coil, carb, brand new high grade marine wires (yes they seated correctly), new gas, new plugs.. I was so stumped I just removed the timing cover to verify that I didnt muck up the timing marks.. anyway got it off and they 2 marks were at 6 (cam) and 12 (crank) as I always do. There was 5/8 play on the slack side of the chain, ive had a prev motor run pretty good even with quite a bit of slack - Either way - Im now wondering if GM ever made a different firing cam? Really have no clue whats wrong.. really at my wits end. Ill try do a compression test 2moro. It seems the motor would only run with quite alot of initial (like 20!) which is why I suspected the timing marks -
also - i never took down the cam but now wondering if the previous builder used a cam with lope (which wouldnt make sense for a big heavy 28 foot cruiser).. but it did wear out the coupler so it might have some real decent power.. 18 inches at idle isnt too bad, but i found it would idle and eventually die (fuel pump works fine).. I might try a full 12v from battery to the coil 2moro to see if perhaps the ignition was too weak..
Yes GM or the marine industry did have a different cam for twin screw boats.. One engine ran backwards if I recall correctly #2 and 8 was swapped . Also there is a 4/7 swap on fire order for certain cams for SBC..
Reverse rotation cam won't even run in a regular direction engine...won't even fire up. Lobe order is different. 4/7 swap is a race deal, not likely to be found in a used marine engine. Typicaly just solid roller cam and solid flat tappet cam, I have never seen a hydraulic cam offered with 4/7 swap.
5/8ths of an inch slack in the timing chain? I admit I have seen them run with the timing chain eating a hole in the cover, but not good! Lippy
First off= The OP doesn't mention twin engines. Hence reverse rotation. Seem's like a normal rebuild/diagnose/repair, and has said to be run on a stand.... But- the slop in the chain has me a lil concerned....... Personally= i'de have changed it out. I'de hope for/assume (lol), we're talking steel timing gears here...... There will be timing fluctuations with a sloppy chain..... Way too much, and possibly jump. Let's hope to hear what transpires with this thread.............And yes- your timing light will go a bit nut's with things....... Should have the chain been a clue?
Fuel new from 3 weeks back, std rotation. Haven't verified damper slip. I'll pull plugs 2mori and verify firing order and do a few compression checks.. Was in the middle if removing crank gear and came home. Its stuck on unbelievably bad.. might have to grind it off.. almost blue hot and still tight. Steel timing double roller yes.. Would I still see 18 inches vac with 2 wires swapped? FWIW timing seemed pretty steady at 10 degrees initial.. I cant see a way this chain would jump a tooth but anyway took a pic if the marks..
The OP asked if there was other cams with different firing orders I just stated that there was to answer his question. may not answer why his engine is running like shit though. And the OP does not say "WHAT" marine application this came from was it a 24 Sea Ray with a I/O or was it a 18 flatty with a V drive that needed a bit more HP for a 4/7 swap? (people do strange things) And Howards makes a whole slew of Hydraulic roller and flat tappet cams for the 4/7 swap https://www.summitracing.com/parts/hrs-114061-08/overview/ https://www.summitracing.com/search...ap-camshafts?SortBy=Default&SortOrder=Default
Check the rockers and see if they are all moving the same amount. I have see many Chevys with worn lobes towards the rear of the block. They don't always run rough, just poorly.
Yeah had every part out.. never checked lift etc. Cane out if a huge 30ft searay triple axle trailer.. lifters weren't stuck at all..
You check a timing chain by turning the crank one way, then back the other way while watching the distributor move. Meanwhile, you look at the timing tab to see how many degrees of play in the chain.... 6-8, you could probably stand ...Double that? Gotta go. However, I've seen them wear a hole in the cover too, and still be running smooth.
I had a supposedly 60k mile 350 I tossed into a stock car to finish out the season, moved my good intake, distributor and carb over to it, set the valves once and went racing. The engine was responsive, would pull strong to 6300 RPMs. Years later I tore it down... found the world's sloppiest timing chain, pieces of this and that in the pan, upon inspection the cam had 4 lobes that were on the way out. Yet it idled nice and made power. With steel gears, they don't seem to jump time like the crappy nylon gears did. So I doubt the timing chain is the culprit as long as the marks on the gears are lined up, the piston is at the top of the stroke and mark on the damper is reasonably liked up with the mark on the tab.
Yeah based on the compression settings this was basically just a new bearings and gaskets build - everything else seemed ok. I wasnt too much concerned with having an exact ring gap - they were around 25 thou which will still run fine on a old fishing boat.. Ill do a comp test today - however rings will have rotated a bit. I have a 30 over kit dished which I might use with vortec heads.. considering the mystery if i dont find an odd cam firing order probably tear the whole thing down and rebore it with my van norman.. Have some nice 193 heads that would also work real well.. max id wanna run this motor is 4000 on the ocean..
If you pulled all the lifters out, did you put them back where the originally were? Mixing them up is a good way to wipe some lobes off the cam.
Those roller timing chains are junk. made in some third world place. they streetch and are loose wnen first installed brand new. Replace it with a good USA made link belt chain & sprockets. Even with a quality roller chain It will not make any increase in HP.
So replaced timing components.. did. a comp test, 145 to 155 on all 8 cold.. plugs were pitch black.. stock jetting on the qj is 44/69 and I might recall seeing 70 or 71 jets.. either way will check power at coil and try another setup. Plugs were new but fouled super quick. At least the bottom end is fine and timing chain though worn would still have worked fine.. I'll update and thanks for the suggestions
Well i think i finally found the issue - fuel pump psi pushing past float.. it was pouring down there after shutting down.. plugs were almost pitch black - that wd explain why now and then she would just run over 3k despite butterflies being closed/idle. Now the stock jetting for the motor on the quadrajet is 69/44 however i found a 70/42 combo- it was puffing smoke etc.. how drastic is the metering on these 2 setups? Put another qjet my wife has been practicing on and she runs alot better and smells right- not so rich. So all I had was fouled plugs!! Oh well you live and learn lol.. at least the new timing set is in anyways-
You're saying 69 primary, 44 rod? probably don't need a 44 rod ..52-54 maybe. 71 primary won't hurt anything either. How old is the float? How much fuel pressure?
Sorry, i mistyped.. I believe rods are 41/42 And jets 68/69.. to quote: For the 5.7L: 068/041 primary & CL secondary For the 350 Mag: 069/036primary and CH secondary The 70/42 just seemed so rich. Installed an inline reg at 3.5psi.. couldn't dial it in with mix screws.. don't know what the deal is.. the
Forget secondary for now. None of those combinations are too rich. Is the float in the same condition at the timing set? LOL. Put in a new float and lower it just a bit from spec.
<ark was thinking of lowering the float but after i plumbed in the psi reg no more drizzling down the throat. I think the fuel pump spring is too tight - the motor is on the gantry so easy to get to.. i prefer not having to run anything inline - ill check fuel psi this week, about ready to drop her back in the hole! Slapped my 5.7 hemi together today so was a little busy with that-
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