compression problems on new motor

[superiormgmt]

Just rebuilt a 350 with a new block and heads. I put it all togather with 80 lbs toque on the heads. I did a compression check and my # 1 cylinder has no compression. Just wondering if this may go away when I actually run this motor?<br /><br />Right now its on an engine stand. I did lossen the valves trying to get something but still no good. Should I take the head off and put it on again. Kinda stuck here, any advice?

 

[paulie0735]

Re: compression problems on new motor

Doesn’t sound good, how are you measuring the comp? Are you cranking with the starter motor? Are you sure you have the cam timing right? Correct length push rods, correctly adjusted rockers? Were the heads and block surface ground? Lots of things could cause your problem but no it won't go away when (if) it starts.

 

[superiormgmt]

Re: compression problems on new motor

I purchased a new rotating assembly used for stock car racing 4 bold main,cam,crank,flat top poistons already assembled. Then added a set of rebuilt heads. right now I'm turning by hand with it on a stand. The block was decked and heads also. As far as I know I've done everything correct. I noticed the problem when atempting to set the valves. I can see the exhust valve open and close on time. I'm tempted to take the head off and try to reseal it.

 

[Don S]

Re: compression problems on new motor

How did you adjust the valves?<br />BTW, what is a good cam for stock car racing is NOT good for a marine engine.

 

[superiormgmt]

Re: compression problems on new motor

The cam was refered to me as a Rv cam or large truck cam

 

[Don S]

Re: compression problems on new motor

But that didn't answer my first question.

 

[superiormgmt]

Re: compression problems on new motor

Probably not the correct way. I was realy just adjusting them until I got compression.

 

[Don S]

Re: compression problems on new motor

I was realy just adjusting them until I got compression.

And you expect that engine to run <br /><br />You've got worse problems coming than just compression if you don't find some kind of manual to work from. Something from what ever era engine you have. Sure hope you know the differences between marine and automotive distributors, starters, alternators, carbs, fuel pumps, water pumps and a lot of other things that go into an engine.

 

[superiormgmt]

Re: compression problems on new motor

I do, and thanks for the help so far. I do have a friend who builds racing engines for a living coming by to set the valves for me. I was just rotating the engine by hand and put my thumb over the #1 cylinder and could not get compresion even after adjusting the valves. This raised my attention. I am using all marine componets for the items listed above.

 

[paulie0735]

Re: compression problems on new motor

ok, well relax for now, having little or no comp when you just rotate by hand is not a sign of disaster yet!! Have your friend adjust the valves for you and while your at it squirt some quality engine oil into each cylinder, make sure you have the correct length push rods and that the manifold is a match for the valley angle. contrary to what many people think, building a V8 engine is not just about putting it together and torque down the bolts. If I had $500 for every engine I have stripped and rebuilt because somebody thought they could do it them selves I’d be a rich man……. Hummmmm actually come to think of it I probably do……… wonder what I did with it all???

 

[superiormgmt]

Re: compression problems on new motor

This is what alerts me to this situanion: I just went and checked again(just for peice of mind). I know this is not the correct way but it does give me a clue if theres compression. Every cylinder but the # 1 has either a strong vacume or presure when I plug the spark plug hole. I've adjusted the valves on this cylinder and still nothing. So I guess I'm looking for a little compression from each cylinder before I have him come and tune this motor. This one dead cylinder is just not making sense to me.

 

[bruceb58]

Re: compression problems on new motor

Very easy to bend a valve if you aren't careful while putting the engine together. Could that have happened?

 

[Bt Doctur]

Re: compression problems on new motor

using an old spark plug break everything out leaving the threaded portion, connect an air hose fitting (weld/braze/tap).screw into cyl, apply air and listen. out the intake manifold, bad intake valve, out the exaust port, bad exaust valve, out the valve cover, rings, wall clearance,cracked piston.

 

[superiormgmt]

Re: compression problems on new motor

Taking a bit of everyones advice the problem seemes to be fixed, Thanks !<br /><br />I put a bit of oil in cylinder, loosend up valves complete. I blew a bit of cirarette smoke in and it was comming out the carb and other spark plug holes.( must be intake valve ) I took a piar of plyers and rotated the valve and....wola compression ! <br />thanks for all the help, I'll be back with more soon

 

[Silvertip]

Re: compression problems on new motor

And the reason that valve stuck open was open is why??

 

[superiormgmt]

Re: compression problems on new motor

That I'm not sure. It did not seem to seet right until I moved it around. It is a rebuilt set of heads. I hope is was just not seeting right and is now ok

 

[Bt Doctur]

Re: compression problems on new motor

hard to understand how it was not seating when you consider the valve and seats are ground first then lapped .?

 

[lilmandavis]

Re: compression problems on new motor

its sticking. stuck. go open not close.oh well let the piston close it when it fires up !!!! didnt hit the valve with the piston already did you??

 

[paulie0735]

Re: compression problems on new motor

I strongly advise you to call the shop who built the heads and let them know, its not unusual to have a stem bind in a new guide. whats more likely to happen is that the valve will stick in the guide in the closed position when the engine gets hot and bend a pushrod. in any case advise the shop and get their ok to proceed, they may want the head back and its a whole lot cheaper now than later. pain in the arse yes but you will kick your self if its turns to **** later. Heed the warning…… things don’t just fix them selves.

 

[paulie0735]

Re: compression problems on new motor

hummm doubled up the post............