Alfa Romeo Forums banner

1 - 17 of 17 Posts

·
Registered
Joined
·
1,771 Posts
Discussion Starter #1
What should the gap between the two ends of each compression ring be after the rings are installed (with the piston still out of the engine)? It's a 2000cc 4-cyl out of a 1975 Spider, standard pistons, Deves rings from IAP.
 

·
1966-2013
Joined
·
13,741 Posts
.0045" ring gap per inch of bore is the common accepted standard unless the rings have instructions that specifically say something different. (doubtful until you get into the more performance specialized multi-piece stuff)
 

·
Premium Member
Joined
·
3,571 Posts
Measuring the ring gap "Out of the engine" doesn't give a true measurement in the actual operating environment. The gap must be measured with the piston in a liner.

What should the gap between the two ends of each compression ring be after the rings are installed (with the piston still out of the engine)? It's a 2000cc 4-cyl out of a 1975 Spider, standard pistons, Deves rings from IAP.
 

·
Registered
Joined
·
2,794 Posts
Slight correction to George's response. You don't have to measure the gap with the piston in the liner, but the compression ring sure has to be. Place the compression ring in the liner about an inch from the top. Make sure it is square in the bore and then measure the end gap with a feeler gauge. The .0045" per inch of bore mentioned previously is a good rule of thumb.

Erik

Measuring the ring gap "Out of the engine" doesn't give a true measurement in the actual operating environment. The gap must be measured with the piston in a liner.
 

·
Trained (ex)Professional, , 1953-2018 RIP,
Joined
·
16,232 Posts
...and to take it one step further, push the ring into the liner with the top of the piston. This will ensure that the ring is square in the bore.
 

·
Premium Member
Joined
·
21,386 Posts
Which raises a question I've had. Do you always need to check this? That is, for stock new pistons, rings, and liners, do they always need checking and trimming, or are they typically OK?

Andrew
 

·
Trained (ex)Professional, , 1953-2018 RIP,
Joined
·
16,232 Posts
Do you always need to check this?
I always do. I've found that the vast majority are okay but every once in a while, I've had to file the gap to obtain clearance. Think of it as always checking new, out of the box sparkplug gaps. :)
 

·
Registered
Joined
·
1,885 Posts
G'Day Guys,

I admit to being ignorant in as far as I haven't rebuilt an Alfa engine yet (or any other engine in the last 30 years) so I'm a bit puzzled as to where the .0045" comes from. I would therefore have used the specs from the manual, would I have been over cautious?

Even the Haynes gives 0.0118" to 0.0177" (for all Alfetta engines).
 

Attachments

·
Trained (ex)Professional, , 1953-2018 RIP,
Joined
·
16,232 Posts
The 0.0045" is per inch of bore. The 2000 engine has a bore of 3.307". So multiply 3.307 and 0.0045 to come up with an end gap of 0.01488"; smack in the middle of the Alfa spec range.
 

·
Premium Member
Joined
·
3,571 Posts
Of course. I wanted to provide a quick response but, obviously, wasn't thinking correctly. It's pretty hard to measure the installed ring gap with the ring and piston in the liner... Fred DiMatteo would have roasted me for such an answer...

Slight correction to George's response. You don't have to measure the gap with the piston in the liner, but the compression ring sure has to be. Place the compression ring in the liner about an inch from the top. Make sure it is square in the bore and then measure the end gap with a feeler gauge. The .0045" per inch of bore mentioned previously is a good rule of thumb.

Erik
 

·
Registered
Joined
·
1,085 Posts
Confusing the issue with facts department.

I opened a box of Deves rings off the shelf and the installation sheet for a 60 to 89mm bore calls for an end gap range of .008" to .014" minium and a maxium of .024".

I generally use Deves rings and set the end gap at .0035" per one inch of bore diameter: or .012" to .014" on a 1570cc engine, with never a failure. Deves recommends end gapping the first and second rings only, never the oil rings, they are preset for the application.

Assembly tip: Wash the liner with hot water and soap to remove all the minute honing grit, and IMMEDIATLY wash the liner with Marvel Mystery Oil and Scott Blue Shop Towels untill the towels show no dark stains. Do one liner at a time. Do not use engine oil to prelube the pistons and rings!!! The Marvel oil will provide enough lubricaton untill the engine starts flushing the liners. Otherwise engine oil prelube can glaze the cylinder walls during the break-in period.
 

·
1966-2013
Joined
·
13,741 Posts
Too tight a gap won't neccisarily cause a failure in the conventional sense, (as in breakage), but it can cause the gap to close up under heat expansion and start to bind the piston in the bore. (on engines with less cylinders, it can actually seize the engine until it cools down and contracts again) If you've got enough cylinders, you'll likely not even notice one going tight as the others will just keep pushing away, but later on it can be detected when doing measurments of the cyliders as it'll kinda hog out the wear area to a slightly larger diameter than the rest of the bore.

Yes, if they go too tight too fast, they can break, but it's not as common an event as piston bind.

If the Deves call for a different spec, then use what they call for, though what you're describing in your own words is for a smaller displacement engine and thus a smaller bore which in turn would be a tighter gap to begin with and not really relevant to the 2L specs.

I'd gap, or check the gap on the oil ring anyway as I've had some 'preset' stuff on other engines do some pretty nasty damage simply because I took the data/instructions at thier word, yet managed to end up with the box-o-stuff that happened to be the one where someone stepped away for a crack hit when it was being packaged so the wrong stuff got stuffed into the box.

Of course there's also the age old trick of getting rings for a .010" bigger bore than what you actually need for a better seal. Those definitely need to be dealt with before installation. :)
 

·
Registered
Joined
·
1,771 Posts
Discussion Starter #16
Assembly tip: Wash the liner with hot water and soap to remove all the minute honing grit, and IMMEDIATLY wash the liner with Marvel Mystery Oil and Scott Blue Shop Towels untill the towels show no dark stains. Do one liner at a time. Do not use engine oil to prelube the pistons and rings!!! The Marvel oil will provide enough lubricaton untill the engine starts flushing the liners. Otherwise engine oil prelube can glaze the cylinder walls during the break-in period.
Thanks for that.
 

·
Registered
Joined
·
4,164 Posts
Do not use engine oil[to prelube the pistons and rings!!! The Marvel oil will provide enough lubricaton untill the engine starts flushing the liners. Otherwise engine oil prelube can glaze the cylinder walls during the break-in period.

Note to self: Pay attention to what George just said!

My experience with Deves rings was comical. I carefully built my engine, used good 20-50 as a prelube, cranked the motor to get oil pressure and then she fired right up. And smoked. Not a problem I thought: all Alfas smoke a little. This wasn't a lot of smoke, but it was a lot more than a new motor should make. So, I did the usual new motor break in driving sequence. It still smoked. Finally, belatedly, much to my chagrin, and to the great humor of my friends who told me to use Hastings cast iron rings ("Do you want to go a hundred thousand miles or a hundred twenty thousand miles. . .??"), I decided that the #@%%$!!!&& Deves rings weren't seating. Then one hot summer day in Austin traffic, the fan failed and the motor got stinking hot before I could get off the freeway and let it cool down. When I felt it safe to start again, guess what? The motor ran just fine, no leaks, no blown head gasket, and---wonder of wonders---no smoking! The Deves rings had _finally_ seated.

In the future, if I ever use Deves rings I will: 1) follow George's suggestion.
2) use a straight 40 weight, non detergent oil for the initial break in miles.
 
1 - 17 of 17 Posts
Top