Hello everyone! Ive got an old OPS .40 marine engine that im working on right now, and I’m having some issues with it; The piston is hitting the cylinder head at TDC. Now either I have the wrong head, or my head gasket isnt thick enough. Ive attached a picture of the engine and head, if anyone has any insight, whether about the head clearance issue or about the engine in general(as i know nothing about these engines), i’d appreciate it. Thanks!
OPS .40 cylinder head
- Thread starter MarkKing
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What head gaskets do you have?
You could just face the squish band until you get it where you want with a gasket.
You could just face the squish band until you get it where you want with a gasket.
Its got some kind of stiff paper for a gasket, i don’t think its right; it should be brass shouldnt it? I could just face the head, but how much? Its a shot in the dark for me. Also, the head doesnt fit tight down in the liner, its got about .030-.040 slop, seems that could cause problems. Im probably just going to have to make another head.
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There being so much slop, it's probably the wrong head button.
Brad
Brad
I had a feeling it was incorrect. If anyone has a head they could measure so i know how it needs to be, i can make one. I can make things, but i’m no engineer
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Put the bottom end together with piston and rod and install sleeve. Measure the depth to the piston top to give you the height of your squish band minus
.008 for clearance and make you combustion chamber like the one you have. This will get you in the ballpark.
Brad
.008 for clearance and make you combustion chamber like the one you have. This will get you in the ballpark.
Brad
Awesome, will update when I get the button done. I hope to run this thing within a week, its eventually going to reside in a sport40 hydro, but thats a whole ‘nother can of worms.thanks yall.
- Mark
I had a feeling it was incorrect. If anyone has a head they could measure so i know how it needs to be, i can make one. I can make things, but i’m no engineer
Don't let the head you have scare you....Take a 1-CC syringe filled with alcohol and measure the volume of the combustion chamber....
If you come up with anywhere close to .37 to .40 CC you will be good to go.....
Don't sweat the loose head to liner fit....After you have run the motor for 15 seconds that area between the head and liner will fill with oil and that OPS .40 will never know the difference.....
Take motor to TDC and measure the piston depth with some dial calipers....Measure the head button depth and determine the head clearance.....Just keep adding shims until you get the clearance you want.....adding squish clearance is easy....the other direction is a *****....lolol
I personally think .008 is to tight for that motor....I would shoot for .012"......That will give decent power and the plug will love you for it.....Good luck.....
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As Rod said I wouldn't worry about the sloppy head fit either. I like 0.012" or so also for my smaller motors, the .90 gets 0.015".
You can make shims by sandwiching shim stock between some aluminum plates on a mandrel, turning the OD then mounting the assembly in a chuck and boring the ID. PITA!
If you measure the bore and ask in the for sale section I'm sure someone has some shims kicking around they'll send you, probably for free.
I'd put new bearings in it and also check the oil holes on the bottom rod bushing line up and it hasn't spun.
You can make shims by sandwiching shim stock between some aluminum plates on a mandrel, turning the OD then mounting the assembly in a chuck and boring the ID. PITA!
If you measure the bore and ask in the for sale section I'm sure someone has some shims kicking around they'll send you, probably for free.
I'd put new bearings in it and also check the oil holes on the bottom rod bushing line up and it hasn't spun.
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Okay, ill see if i can buy some shims before doing all that
-Mark
Good stuff!
Is it really a 40? Or a 45?
From the looks of the crank and the exhaust header I'd say a 40, if so where did you find new piston/sleeve and rod? Are they really 45 parts that drop in?
If so maybe the 45 rod is longer than the 40 rod?
Hmmm....
I bought the engine off ebay, the new parts were already in it. I guess its possible the rod could be for a .45. Ill post the center-to-center length when i get home.
Once again shims are not a problem and they don't have to be perfect.......You don't need OPS shims to get what you need.......
Measure the diameter of the head and get shims from any motor that has a bore close to that diameter...... I guarantee there is a motor out there that has shims that will work.....
that have a bore close to that dimension and the I.D. and O.D. you need.....all you need is a seal....any little cracks or crannies will be filled with oil
after that initial 15 second run.....
Your main concern is the thickness of the shims not the I.D. and O.D. ...... you just have to be in the ball park.....as long as it seals.......
If you want to know an easy way to CC the head....call me.... 1-715-926-6096 .......
What you doing here is not high tech and it doesn't need to be.....The motor will never know the difference....
Rod Geraghty
Thank you for the words of wisdom Rod. Im fairly confident i can handle it from here, but if i get tripped up, I will give you a call!
I wasnt thinking when i said id get a measure on the rod. The engine is all buttoned up, besides the head. Im not taking it back apart, I hate cleaning loctite out of screw holes
so i guess well never know. I did measure the bore though, it is .863; also, at TDC, the piston is .154 below deck, Terry, do you have one of these engines that you could compare with?
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Mark I have 2 45 OPS engines and just measured the bore which is .854 and the distance from the top of the piston to the top of the sleeve is .116. My head button depth is .106 giving me a HC of .0010 which is what Andy Brown suggested/ .008-.010 is good
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Did you factor in your gasket when figuring squish?
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