Yes, I have used this method numerous times on the five cylinders as well. It is SUPER EASY on a four cyl, but on a five it is CHALLENGING! but it can be done. You just need to make up a few new swear words.

The comment about compression numbers not being the be all, end all reminded me of something.

When my industry died it's slow, agonizing death I worked a little over a year as a Fork Truck Mechanic in a HUGE diaper factory. Most of the trucks were electric with modern electronic motor drives and such, but there were a few LPG trucks or IC(Internal Combustion) as known in the Fork Truck industry.

When I came to the shop there was an old Nissan 10,000 pound lift truck that legend had it was the first fork truck that ever showed up on the premises when they were building the plant in 1983. The construction people used it and it has been in the plant ever since used for everything under the Sun.

It had a gazillion hours on it and the guy before me told them that it had no compression and needed to be junked. The engine looked EXACTLY like the 6 cylinder in my first car, a 48 Chevy.

The old thing had it's problems, but I ran a compression test and it had about 90 to 100 all across a little low for this gas engine. It wouldn't start and I found a very weak spark. The points were pitted and almost closed up. I filed them and opened them up some by eye and the old thing started but sounded like it had a knock. My boss was excited because he had gotten so much pressure to junk it.

I put the old truck at the end bay of the shop and worked on it in my spare time for about a week. I adjusted the valves, got some new points, changed all the fluids and got it running well enough that they bought an expensive set of tires for it. Winter came and it got hard to start, but I rebuilt part of the LPG apparatus called the vapor generator and found a bad gas hose. The radiator started leaking so I pulled it and sent it to the radiator shop. I got a Pertronix points eliminator and put in the distributor.

I was the hero of the maintenance people in the plant because everybody loved the old machine. For some reason they called it "Pedro."

Remember the knock in the engine. We used that old truck for about six months after I got it back in service and it had a crazy engine speed related knock that I could never figure out. One day somebody came and got me and said that Pedro's motor was locked up. I was about half sick when I went and found the starter wouldn't turn it over.

I started investigating and found that a small driveshaft off the harmonic balancer that drove the hydraulic pump had destroyed itself and was keeping the motor from turning. I got a new shaft and replaced it and I KNEW that this was the source of the knock. Once I got that shaft on there, it sounded like a Cadilla... er' a Mercedes Benz.

I still work in the plant but for an automation company. I see Pedro go by every once in awhile and he sounds really healthy. The maintenance people make comments to me quite often that I was Pedro's saviour.

SOOOOOooooooooo............... Don't EVER give up on an old engine based on compression numbers alone. If it makes enough compression to run, doesn't use too much oil and has enough oil pressure, it wants to go on living instead of finding it's way to the scrap pile..... Just ask Pedro!

Good story Larry. So good that I might have to include a quote in my signature. Incidentally, I bought a HF compression tester last week to check out the 240D. It has a fair amount of blowby, but it starts up, has good oil pressure, and as far as I know doesn't use much oil between changes (although I honestly haven't driven it enough to know how much for sure). Now I am motivated to check out the numbers - maybe I will do that this evening.

With an old diesel, some blowby, no problem. If it starts, has a little oil pressure at idle and you can carry enough oil with you to get where you're going, it's good for the road.

It doesn't take a compression test to answer the questions in the previous paragraph. In fact, unless I was looking for the source of a dead cylinder I wouldn't bother with a compression check. It might make you feel bad. Just enjoy it.

what temperature was the engine?

It was a cold engine... so that must be it.

you're fine.

it is nice to compare the hot numbers with the warm numbers to give more insight.

Don't forget to use the injector heat shields when using the injector adapter.


My wagon has worse cold comp numbers and still gets 23 mpg. footnote* Larry


maybe post your warm numbers for everyone to see the difference?

Cool, thanks everyone! Now I will do the valves and get my motor mounts changed, and do the front suspension and so on :D

-James

Here's what my inj adapter and glow plug adapter look like next to an inj and glow plug.

Note the inj adapter schrader valve screws in at to hex end. There is a big round cavity from the tip of the adapter up to the hex probably about 1/2" dia 2" L. This cavity lowers the compression ratio and gives the lower reading than the glow plug adapter.

Is your inj adapter like mine or different?

http://i31.photobucket.com/albums/c3...1610_001-1.jpg

Mine is the same however you are missing the collars on the injector adapter. I can't imagine this volume will make much if any difference.

What collars and where do they go? In the adapters I have, It makes 60 psi difference (measured). That is a lot! Why do you think they make different thickness head gaskets? It is to dial in the compression ratio after piston protrusion is determined.

Note the glow plug adapter? It is missing the volume of the heating element. That little bit of voulume missing will also lower the compression ratio and lower the actual compression numbers.

What does MBUSA use? There is a collar that sits around the base of the injector adapter. if what you say is true, the hose to the gauge is probably the biggest loss of compression. How did you measure the 60psi difference? I find it hard to believe that it makes for 4bar difference.

How Do You Figure?
 

Hi
I'm trying to follow your logic here but can't quite make it.

OK, the injector adaptor with opening 1/2 inch X 2 inches adds about .78 cubic inch to the volume of the cylinder which is about 36.6 cubic inches - or about an additional 2% volume. Given a normal compression reading of 400psi - how could a 2% increase in volume reduce the compression reading by 60psi?

Also, when you remove the glow plug, you also increase the volume but a lesser amount.

Either way you test, the added volume of the tester hose and guage are the same and doesn't make a difference.

Perhaps a math whiz on the board can shed some light on the problem.

Regards,
Joseph

The logic is that the volume of the combustion chamber changes with the adapter as oppsed to the volume with the injector. This changes the compression ratio, thus changing the pressure.

This logic is correct, but it's a moot point. The more important value of a compression test is when trying to find a weak or dead cylinder and then trying to determine the cause. If the numbers are the result of a lower compression ratio it doesn't get in the way of getting the data needed from a compression test.

Final volume matters more. If the volume ratio is about 19 with an injector, then the TDC volume is about 2 in^3, closer to 3 w/ the extra volume, I can see your point. The volume ratio the extra volume will be about 19 (2 in ^3 / 2 + delta in ^3). Have to look at mine now.