Decision time, need some input.
 

Hello everyone,
My beloved 240D recently made a very poor showing on a compression test, and as you know, when that happens you basically have three options, none of them cheap or easy. My question is; If I opt for a rebuild, how much can I expect to spend on parts? Any input is appreciated.

I think someone here has some 616 and 617 rebuilt motors for sale.

How bad we talking?

There are some pretty extensive 616 rebuild threads in the archive and there's this absolute banger on youtube: https://www.youtube.com/watch?v=44-twsAtO0Y&t=265s

It's been a while since I've read, but from memory there are an obscene number of variables re: how many components are still within spec and reusable. You're likely looking looking at thousands one way or the other.

Rollguy is the man to ask.

Did you do a valve adjustment?

Do a leakdown test to find out what's wrong.

Are you doing the rebuild yourself, or will you pay someone?

What he said.

Lots of missing information to be expecting an informed opinion.
 

How many miles on the engine? When were the valves adjusted last?

I suggest you stick with this engine until it's certain that it is worn out.

Logically if the engine turns out to be really bad. The easiest bang for the dollar is to find another pretty good used engine. You may be in th best part iof the country to still locate a good one fairly cheap.

The old days are gone.Any work inside that block will usually be expensive in comparison. Although unlike the tubo 617 engines the pistons are not six hundred apiece.

How many miles on the engine or whole vehicle was always an important consideration to me. The problem about this simplistic approach was there were so many variables.

For example the wives car spends in excess of ninety percent on the highway with all Fluid changes kept up. Driven in a reasonable fashion. Versus a car infrequently seeing almost any fluid changes and only used for short local trips. The wives engine could be in better condition at twice the milage easily in my opinion.

As cars get older some people totally ignore oil changes pretty much is common. Even worse is they run oils were the viscosity was lower than the engineering of the engines required. Old dilluted and seriously contaminated engine oil is going to create wear a lot faster.

Combine this with a very high rate of cold startups in service. You are not going to get the lifespan available otherwise.

Perhaps the OP can offer some data on how the car has been handled over the years.

Thank you to everyone who responded. Here are some answers to the questions.

My brother and I had done the valve adjustment just a few weeks before the compression test. The car had been having issues with hiccuping and misfire on cold start that were getting more pronounced over time, and we were hoping the valve adjustment would help. When it didn't, I opted for further diagnostic work, hence the compression test.

There are 362, 000 miles on the odometer, but the engine had been replaced by the previous owner at around 309K. I do not know how many miles were on the replacement engine. I've owned the car for over five years, and put on about 43,000 in that time.

I would be hiring someone to do the rebuild-that kind of work is beyond my current skill level. I have a neighbor who can do the job, and he has advised me that the parts will probably be the biggest expense.

I hope this answers the questions. Thank you again.

As previously suggested, do a leakdown test the perhaps use some suitable carbon solvent to dissolve prospective carbon buildup on rings which is possible to have frozen the rings.

Cylinders get a taper after years and miles of wear. The upper portion is sometimes a bit larger in diameter than the lower portion. The piston rings may start sticking at any point but the lower diameter of the cylinder always determines their final resting point if they seize.

This may seem like a lot of trouble but some oils are capable of breaking the carbon loose. Some folks run a portion of sea foam in their fuel tank to prevent this. There are many good folks here who know much more than I about these low compression issues and will help if you ask.

I do not mean to discourage you from rebuilding the engine if you have set that as your goal.

It is easy to get bad measurements from a compression test. Examples - the fittings must displace exactly the same volume as the parts removed (injector or glow plug), the Schraeder valve at the tip of the compression fitting must be proper (white ring w/ weak spring) and seal well, the hoses and fittings must not leak.

Even if low compression, you should find the culprit. As mentioned, run a leak-down test for that.

Try a poor-man's test. Turn the engine over by hand and feel for each cylinder resisting you. If you must stop and wait a few seconds for each one to "hiss down", that suggests excellent compression. I use the bolt on the p.s. pulley at top (22 mm wrench, I recall).

If you truly must rebuild the engine, at least non-turbo pistons are available and affordable. I doubt your neighbor can rebuild the engine competently without taking it to a machine shop. Usually, the cylinder liners are replaced and then machine-honed to match the pistons. One also needs to "deck" the top of the block since the new liners protrude.

There are plenty of working used engines. A member here is offering rebuilds for $5k but/and has a reputation for good work. The used engine shouldn't be too difficult to get running on a stand before installing.

Dad used to say "you pays your money and takes your chances. A proper diagnosis before doing anything is important.

Thanks to everyone for the imput. If there is a way to fix this problem short of a rebuild, I'm happy to hear about it.