Compression Readings and Oil Pressure For New Engine

Ok, so just wanted to double check this i`ve built a new 1915 engine - run it up, etc. I caclualted all the deck height and head ccs so i`d end up with about 8.6:1 ish compression ratio.

In order of checking with all plugs out, engine cold and wide open throttle, i got -

1 - 170psi
2 - 170psi
3 - 160psi
4 - 155 psi

How does that sound is that too much (!) or looking ok?

Also, my the oil pressure when i started it up was about 2 bar at idle with the engine cold - i wired the pressure gauge to the wrong terminal on the sender when i ran it in for the 20 mins initially so don`t have hot readings (doh!), although the oil light didn`t come on at idle when hot so guess thats ok!

Does that sound about right aswell?

Cheers, MIke

What cam do you have? 8.6:1 with a stock cam will be too much and will run really hot and detonate. For a W110 is perfect.

Compression should be measured with the engine hot.

Are the barrels/pistons/rings new? The rings will have to run in to get properly seated first, then you can measure the compression for a more accurate measurement.

What oil you using? The rule of thumb is no less than 10psi per 1k rpm hot with 30 weight. You should expect more in a new engine at idle.

Abel

Yes - engine isn`t in the van yet - hopefully get it in on friday and drive it out to seat the rings in. I`ll measure the compression again once thats done and when the engine is hot.

That 25 psi at idle was when the engine is cold - will get a better reading once the the engine is hot. Obviously it will drop when the engine is hot, but i was wondering if it should be a little higher when cold at idle.

Oil is SAE 30 golden film stuff.

Engine specs is -
1914cc 94mm barrels
stock crank
stock cam
1.4 rockers
stock heads ported and polished with 3 angle job
complete crank assembly balanced
compression set to about 8.6
dell 40s with 32 vents
4-1 exhaust
stock complete tinware
123 ignition dizzy
addtional ext oil cooler on thermostat

How come it will run hot with the stock cam then? I ran a 1641 in a van 2-3 years with the same sort of spec as above but with 9:1 and it ran cool as a cucumber - no external oil cooler either there.

Thanks, Mike

I would expect 25 psi at idle when hot on a properly rebuilt engine with all tolerances as they should.

Your dynamic compression will be to high for this cam, plus you using 94 barrels which produce a lot more heat.
Oil temp is one thing, head temps is another. Your cylinder pressures will be too high.
I am just giving advice, take it if you like.

40 Dells are great, but change your vents to 28 or max 30 as the 32's are too big for your combo. There will be no benefit whatsoever using them due to the cam stoping to make power rapidly at around 4k. They can be more tricky to tune due to the intake valve size too.

This engine will be a torque monster, but will not make power up top as it would if it had a different cam.

Abel

Thanks - no appreciate any advice!

Thats a little bit concerning about the oil pressure - but will run it up hot tomorrow morning probably and see where it sits when hot. I did fit a new 26mm oil pump which i sanded down the cover surface to make it perfectly flat. Used the thin paper gasket there with no sealant.

Yes - i went for the 94s - knew they would run a touch hotter, but i couldn`t afford a stroker crank and the clearancing for it - same for the cam, so used what i had from my old engine - 1.4 rockers, dells, heads, etc.

i do have some 28s from old engine and assocaited jetting, but i`ll see how it goes for the minute. I was aiming for a torque monster as i won`t revving it much over 4.5k. I `ll have to coupled to a 6 rib late bay box.

If you`re interested, this is the 1641 i had before - it was rebuilt stock bottom end (not by me), then i did the top - same spec as above, but 1.25 rockers, 9:1 compression, 1641cc, 28 vents-

It made good power and torque all the way to 5k rpm -

Nice chart, good power for a 1641.


Abel

Thanks - so curiosity got the better of me and drained the oil a took the pump cover off.

You can see on the pump cover where the bottom of the bottom gear has been catching the cover plate.

But no marks from the top gear - I checked the top gear and I think it does 0.003-0.004 inches lower than the mounting surface. So that can't be helping I guess!

I'd a new shadek pump aswell which I'm sure I sanded down! Looks like I'll be doing that tomorrow!

Also - just measured the gasket I used - is 0.012.

I have 3 spare cover gasket - one is 0.009 and the other two 0.004 - talk about consistency - guess which one I'll be using when I put it back together!

Looks like you found the oil pressure culprit

That shows how the little details can make a big difference. Well done
There are engine builders AND engine builders.

Abel

Thanks -this is my first engine build from scratch learning every minute and appreciate any advice!

Put it all back together this morning and ran it up - got a whole extra bar of pressure at cold idle - 3 bar. Went down to just over a bar at hot idle so still not where i would want it to be but moving in the right direction. I guess my engine building skills are still not quite there yet although it has new crank and cam bearings. I remember the oil cooler relief plunger was difficult to get out of the case but once out, i cleaned it up and once in the bore slid up and down nicely. The other plunger was a bit looser and practically fell out - i imagine thats where i`m loosing the extra bit now.

What did suprise me was when revving it up on the engine stand, that when it hit about 2k rpm, it was like the engine wanted to rev and was almost pulling the throttle open - never had that before! Guess its the 1.4 rockers and the fact its balanced aswell.

Scratch what i put above - let it idle for a while to get properly hot up to 80 degrees and the gauge i have is actually showing less than 0 bar although it does rise when you rev it. It did rise nearly a bar though when cold at idle so the improvements i made to the oil pump install had an effect.

Factory oil light is still out though and not flickering or anything.

Can`t understand it at the mo. I`m using a second hand off ebay 10 bar VDO pressure gauge which came with the 10 bar dual pole sender - sender is not vdo though by the looks of it and made in hungary so I`m going to try another gauge and sender tomorrow to eliminate that before drastic measures are needed..

So I finally have some oil pressure but maybe not enough yet!

I splashed out and bought a new oil pressure gauge and a sender. I also removed both oil relief springs and changed the shorter control one for one from another engine - mine was 30mm - other one was 32mm. Both plungers moving well and no play in the bored.

Also removed the stock oil filter and cleaned it as was getting a bit clogged with assembly lube which must've washed down to it

With all this done together after idling for about 25 mins and at about 60c, pressure is about 20 psi which rises to about 40 psi at 2k rpm -increasing to 3k rpm gives 45psi.

Not sure what else to do now - I have visions of a cam bearing dropping out on assembly or one of the crank bearings being over sized, but if this was the case I'd have hardly any pressure?

I tempted to invest in a decent well manufactured oil pump like the 26mm CB performance one.

The higher pressure springs for the oil pistons will only increase pressure at high rpm's, it does nothing at idle or cure low oil pressure problems on worn out engines as many believe.

20 psi would be good if the engine was idling at the correct working temperature. At 60 deg the engine is not fully warm and the oil is still slightly thick, so pressure will drop after a long run when coming to a stand still.

Probably you have too much clearance on the rod bearings, and/or rod sideplay. In your case, if you used a 30mm pump you would increase the oil film thickness and therefore it would create more pressure. Also a 20w50 oil would do the trick.

Abel

Thanks - I wasn't going to fit any aftermarket springs - just put in a less worn one. Fittedd new big end bearings but bought some 20w50 oil to stick in it. Have to admit didn't check side clearance but rods dropped fell uniformly.

Engine is in the van now so just connecting all the bits up and have to install the gauges - will see how it goes once running again