The V8 Owners Forum -

Hi, Finally got my chevy v8 engine running after I rebuilt it,a few problems have occured,first the engine overheats within 4 or so minutes,so I cant break cam in properly,secondly when I turn off engine the engine runs on for a few seconds then two really bangs in each exhaust,I set timing about 34 degrees,cant understand whats going on,Any ideas,cheers dave

are you setting the timing with all vauum off the dissy, at the correct RPM

Hi,using mallory dualpoint dizzy,mechanical advance,Im sure all the advance was off,if retarded would that cause overheating?

it can do. Are the header (exhausts) turning red?

My 4.6 started to overheat during the cam running in phase, basically I had to blast the rad with a hosepipe constantly, even then the temp remained around 80 degrees. I guess that the cooling system just ain't supposed to cope with 2.5Krpm and no air flow through the rad. (I would not count on the fan to provide enough airflow)

Also your coolant system is likely to be full of air, you need to run the motor with the rad cap off and have someone topping up the rad, as soon as you think that it won't take any more fluid then stick the cap on.

Running in a cam is a bit hairy, it helps to have a couple of friends around.

My engine also run on and popped and banged through the exhausts. I guess that they don't like being turned off from 2.5K!

Good luck!


Pete

What compression ratio are you running? Both of mine run on on petrol because the compression ratios are >10:1 and timing is set for LPG.

Chris.

The engine is running about 10 perhaps 11 to 1,Im using 1969 camel hump heads which really need leaded fuel,have used a lead subsitute to help,how important is the cam break-in? The engine ran about 3000 rpm for 4 minutes then got really hot,so I turned it off! Will check airlock next time I fire it up and timing again!
I did have worries about waterpump so have changed that and ordered some seals for carb as they were leaking from float bowl transfer pipe!
What temp should the chevy be running at? I have 180f in my head from somewhere is this right,cheers Dave

Hi
With the 350 chevy, if you are running in a flat tappet cam it is very important, 2 to 2.5 K is the range to go for from the reading I have done, but I suspect 3k won't do any harm just it will get hot, you need to be using a Deisel engine mineral oil single weight viscosity if you can get it and lots of cam assembly lube (the molibdimum disulphide one). Acording to the Primmedia magazine titles (hot rod, car craft) this is a big issue with Chevy flat tappet cams. if it is a roller cam then no molibdimum cam lube, the other one that is red or white depending on who makes it and you don't worry about running it fast at first, run in a roller cam as if it has been in forever and run in the bearings.
Mike

Thanks for all the information,will be starting it up again this weekend,just fitted new waterpump to help and new temperature gauge,cheers dave

dave350v8 wrote:Hi,using mallory dualpoint dizzy,mechanical advance,Im sure all the advance was off,if retarded would that cause overheating?

Sounds like your timing could be way out. I'd suggest setting it to 12 degrees static or thereabouts and then add 20 degrees for the mechanical contribution. I'm assuming you haven't dialled in 34 degrees across the board, from cranking?

Hi, checked my timing again,replaced waterpump,started engine temperature rose to 190f within few minutes,bubbling in expansion tank,turned off again engine ran on then big bang in each exhaust,Im using a transit diesel radiator perhaps this is too small,never seen an engine get so hot so quickly,Is it worth checking if cam timing is a tooth out,may have to think about possible cracked block or heads,did have engine bored out to +60,these engines dont like max rebore due to thin cylinder walls!

Does this engine start easily? Timing isn't 180 degrees out? Cam could be mistimed as you suggest.

Take the thermostat out and try again - could be restricting flow too much

Ian

Hi,checked my dwell angle on points this was way off,set it up with new points,checked timing after which was then wrong reset this then fired up ran fine and stayed cooler around 200f which is ok ,so really pleased thanks for all your help!