how much blowby is acceptable?

[Leftcoaster]

I've never understood how the "wet test" could be considered a reliable method of checking ring seal unless say 1ml of engine oil was evenly distributed between the 85mmd bore and piston directly above the top ring for a full 360 degrees

I once checked this method with the head removed then smartly rotated the engine at around 200rpm, as a starter motor might with an assembled engine

The oil rapidly formed streaks on the bores about 1/4" apart, with no sign of being evenly distributed on the wall and top ring sliding surfaces

Yes, the compression pressure of a rotated assembled engine might have caused the oil to evenly coat the wall and rings, but if 1ml is merely squirted through the spark plug hole onto an 85mmd piston crown I cannot imagine what forces would cause its even distribution unless one relied on gravity with a low viscosity oil, high ambient temperatures, and waiting at least 24hrs

My suggestion is the higher compression reading you observed was due to the combustion chamber volume being reduced by 1ml while the swept volume remained constant

[user-23911]

Compression tests don't work the way many think they do.

For example with a turbo engine, it's common for them to detonate when over boosted, they blow smoke. Do a compression test and the numbers will usually be higher not lower.
The big clue here is that the plug threads are oiled up.
When you pull them apart you find oil on the piston tops, the ones with the highest comp numbers have the most oil and are the most broken......then when you pull the pistons out.......the ones with the highest comp numbers have broken ring lands usually between the 1st and 2nd rings, sometimes above the top ring, sometimes also broken between 2nd and oil rings.
Of course if you totally destroy them then the numbers will be down but the numbers tend to go up with damage, before they go down.


There you go....think on that for a bit?

I've always considered a comp test a waste of time (on a smoking engine), just pull the plugs and inspect them.
A comp test is good for a fresh engine to give a baseline number for reference for after you've broken it.



If it's an old worn out engine and the comp numbers are down, it's often because the rings are stuck to the pistons, stuck with old oil deposits, they cant seal to the bores when they're stuck.
That's never going to happen on a new build.


As far as "break in " goes......."drive it like you stole it" has always worked for me.

[digger]

I've never understood how the "wet test" could be considered a reliable method of checking ring seal unless say 1ml of engine oil was evenly distributed between the 85mmd bore and piston directly above the top ring for a full 360 degrees

I once checked this method with the head removed then smartly rotated the engine at around 200rpm, as a starter motor might with an assembled engine

The oil rapidly formed streaks on the bores about 1/4" apart, with no sign of being evenly distributed on the wall and top ring sliding surfaces

Yes, the compression pressure of a rotated assembled engine might have caused the oil to evenly coat the wall and rings, but if 1ml is merely squirted through the spark plug hole onto an 85mmd piston crown I cannot imagine what forces would cause its even distribution unless one relied on gravity with a low viscosity oil, high ambient temperatures, and waiting at least 24hrs

My suggestion is the higher compression reading you observed was due to the combustion chamber volume being reduced by 1ml while the swept volume remained constant

I don't think 1cc would equate to 10-12% increase

[user-23911]

A teaspoon is not far off 5 cc.
I don't know how you'd get 1 cc in and make any difference.


Did you tell your machine shop what you did?

[Cubic_Cleveland]

You mention not exceeding 50% throttle during break-in. Recommendations vary, but many (including me) feel that short bursts of WOT are important for ring seating. At this point I'd try flogging it as hard as possible to see if the higher resulting ring forces can do the job.

Yeah, pretty much we get the engine to temp, check for leaks, timing, lash. And beat the piss out of it until it makes what it makes.

I don't see any reason in pussyfooting an engine. If it's meant to spend its life a 2000rpm, cool.. but thsts rarely the case.

Unless you bought some rings from 1960 that need to be lapped into a round shape, run it like you stole it.

MadBill and Headguy have it right, give it a hard time. Some of the engines I build are competition only. They get run up on the dyno to make sure everythings right, then sent out to race. There is no “light load” run in..

[AC sports]

Lol. You guys made me laugh at myself. Yeah I agree. The increase in psi is probably due to the volume decrease of the chamber. Looking at my syringe again it was a 5ml not a 1ml shot I gave it. If I decrease the volume of my combustible space by 5 cc then my c/r hits 11.75 :1 from the current 10.5:1
That's more likely where the increase is coming from.
Now the question is; why do they teach the wet test in automotive school?
Not that It's my background.

[Tom Walker]

"If" a compression check is done properly, along with all the observation and diagnostic skills you have, I have found it can reveal information on an engine relating to its health, especially an engine you have a history of compression checks on. You can see a pattern that is cosistent, or deteriorating. I agree, by it's self, could be misleading information.

[bentvalves]

so what was your method of cleaning them? did you skip the boiling hot water/dawn dish soap/bore brush/toilet brush method of "floating" the honing grit out of the cross hatch and go straight to rags and solvent?

[AC sports]

I consider myself obsessive compulsive when it comes to parts cleaning.
Bores were pressure cleaned along with block then scrubbed with hot soapy water, then solvent then atf with white shop towels. They were clean.

[user-23911]

Now the question is; why do they teach the wet test in automotive school?

If you can't actually do it....you teach it instead.

[ptuomov]

I consider myself obsessive compulsive when it comes to parts cleaning.
Bores were pressure cleaned along with block then scrubbed with hot soapy water, then solvent then atf with white shop towels. They were clean.

How exactly do you know that you have a problem?

[MadBill]

Now the question is; why do they teach the wet test in automotive school?

If you can't actually do it....you teach it instead.

So if someone was to spend two thirds of a lifetime "doing" at the highest level and the last third mentoring and passing on his expertise to the next generation, he would by definition be a washed-up loser?

[Leftcoaster]

Some 50 years ago Caterpillar sold a "Break in Powder" p/n 7F5225, reputably non other than Bon Ami, to encourage ring break in on their large capacity low rpm engines

Local lore was 1/2 a teaspoon was very carefully admitted at high idle over a minute or two after loosening the air cleaner to intake manifold connection

Never saw or used it myself as the IH, Cummins and Detroit Diesels we overhauled sealed satisfactorily

Right now JEG's are advertising "Total Seal Quickset Dry Assembly Lube", which their ad paradoxically states is a powder - -

If the OP's only alternative is to pull the pistons and re hone, powder may be worth a try - - if it doesn't work and assuming he uses a minimal amount unlikely to cause scoring or other damage, he'll face nothing worse than - - pulling the pistons and re honing

An unconventional alternative would be to run the engine without an air cleaner

Lastly, the importance of compression pressure in creating ring seal was proved when I once attended a newly overhauled Detroit Diesel 8V71 installed in a crawler tractor, after it had worked for over 100hrs on 7 cylinders due to a faulty injector

Pulled the injector to find the bore beautifully "glazed" and as shiny as a mirror, told the owner we had nothing to lose by fitting a new injector and running it - - three months later they ran it out of water and when stripped the previously glazed bore looked identical to the others

[user-23911]

"Brasso", as in metal polish, there was a myth circulating that you could use it to fix smoking engines.

A local mechanic had a van of his own which was worn out and smoked a lot.
Prior to getting a proper rebuild (toyota diesel work van)he did the brasso trick just to see what happened.

It made it worse.