Author Topic: Understand Compression results (Read 3762 times)

TD_Bunny · « **on:** November 20, 2007, 09:21:51 pm »

So i have searched and read all of the posts relating to this subject but i thought i would ask my own version of it anyways. I got my car compression tested today and here it was they came up with:

325-400-410-450 cylinders from 1-4

I clearly have under the 398psi limit listed in the bentleys and have greater than a 70psi split between the #1 and #2 cylinder. Apart from just getting bent over on a deal, i am stumped because it was a rebuilt engine with less than 20k miles on it. I have owned the car for only 10k or so and have kept up with reg oil changes using AMSOIL synth. Someone please tell me it is possible that i just need to have my valve adjustments checked since i dont think they have ever been retuned since the rebuild or is the split of compression way too big for that to be a possibility?

I was thinking of have a shop check the gaps but if that seems like way too far fetched of an idea then i dont feel like wasting my money any further. BTW, i still get 43-47mpg depending on how i drive and she fires up like nothing every morning. And i just had new injectors with fuel lines replaced so my gas milage might even be higher now. Well the more opinions the better so any suggestions would be nice. thanks.

Keeping my TD rabbit going just might be the hardest thing i have ever done

OM617 · « **Reply #1 on:** November 20, 2007, 09:36:31 pm »

Synthetic should never be used on a rebuilt engine until it's passed at least 20,000miles.

Newer engines use synthetic from the start because they are designed with that in mind. Synthetic oil was still rare when the IDI engines were made so they must use dino oil for the break in period. Synthetic effectively prevents wear and will prevent the parts from seating properly and creating a healthy wear pattern.

TD_Bunny · « **Reply #2 on:** November 20, 2007, 09:42:27 pm »

hey fastest response time ever! The engine was warm enough for me the drive it to the shop and then i am not sure when they started on it but it would def not be cold. could not say for sure though. As far as oil, what the heck then now i am S.O.L.? I did not know that about the IDI needing good ole dino oil but now what do i do?

Vincent Waldon · « **Reply #3 on:** November 20, 2007, 09:50:35 pm »

On the one hand, your bunny is running perfectly... starting well, giving you great gas mileage... perhaps a bit of Alfred E Newman is in order "what, me worry" ??!!! ;-)

On the other hand, one cylinder does appear to be low... I concur that synthetic oil is not the best break in oil, but I wouldn't expect only one cylinder to be this far behind the rest.

Can't remember the valve adjustment intervals but maladjustment on #1 could certainly cause the low number... or do a leakdown test (which doesn't care about valve adjustments)... might reveal a burnt valve rather than rings that are not broken in... were your old injectors high mileage ?

Or a ring broke in #1 during install and it's always been a bit low, and gonna stay that way.

IMHO... 20K is just the beginning of a diesels life and they are slow to break in if left to their own devices, particularly if you've been running synthetic the whole time...darn that diesel fuel and its natural lubrication properties. There are techniques to speed up ring seating etc but that ship has sailed by now.

I've be inclined to check the valve clearances, do a leakdown if you can arrange it... otherwise perhaps let er go for another 30K and then check back in to the compression.. or sooner if it starts to develop symptoms... so far she sounds a treat !!!

OM617 · « **Reply #4 on:** November 20, 2007, 09:52:43 pm »

Exhaust all the other options before you decide you are SOL.

Do a leak-down test, it will tell you where the air is escaping. There will always be some air passing the rings, it's the nature of piston engines, but if the rings or piston have not seated right there will be noticeably more air passing into the crankcase from the #1 cylinder.

TD_Bunny · « **Reply #5 on:** November 20, 2007, 10:09:40 pm »

thanks for all of the input guys. I am actually going to call early tomorrow morning and see if i can get squeezed in for a valve adjustment just before the holidays. Judging by the bentley's that should not be too expensive on labor to have done. I guess i am just a little anxious to not have any problems since i have tried to do so much to it so far. I had planned on getting over 1000 more dollars put into it until i got the readings back. I tell ya, my car does not look like much but underneath its practically brand new

Vincent Waldon · « **Reply #6 on:** November 20, 2007, 10:34:30 pm »

Quote from: "TD_Bunny"

thanks for all of the input guys. I am actually going to call early tomorrow morning and see if i can get squeezed in for a valve adjustment just before the holidays.

Let us know what you find... inquiring minds want to know !!!

Vince

TD_Bunny · « **Reply #7 on:** November 21, 2007, 07:57:42 am »

I have an appointment for tuesday morning so i will keep this post updated until i find out what is going on. I just put in a quart of Castrol GTX 20w-50 and i will change out the rest this weekend for a new oil change on dino oil. I'll check the oil consumption also every 500 miles to get a rate for oil loss using dino to see if it begins to reduce. I am going to have them give me the measurements for the gaps so I will also post the results when i get them. Thanks guys.

jtanguay · « **Reply #8 on:** November 21, 2007, 08:19:47 am »

Quote from: "OM617"

Synthetic should never be used on a rebuilt engine until it's passed at least 20,000miles.

Newer engines use synthetic from the start because they are designed with that in mind. Synthetic oil was still rare when the IDI engines were made so they must use dino oil for the break in period. Synthetic effectively prevents wear and will prevent the parts from seating properly and creating a healthy wear pattern.

should also note that dino oils arent what they used to be. they used to have things in them like zinc etc to help reduce friction. but yes, dino should be used to help the rings seat.

TD_Bunny · « **Reply #9 on:** November 27, 2007, 02:20:41 pm »

Small update, the shop had to adjust 0.10mm across the board which the head guy said you usually see with a rebuild. Guess I just did not luck out with mine

I will update this post when i get home with oil consumption using half 20-50 dino oil(all i had at the moment) to see how much i used over 500miles. I will also post what the mech. gave me as far as technical measurements for you all to look at. At least i should now have a little more compression. Also once again, it was about 40c this morning and started up without have to crank over at all. As soon as the key turned I was up with only a minute or so of exhaust smoke.

Later

TD_Bunny · « **Reply #10 on:** November 27, 2007, 05:41:16 pm »

Cylinder:
#1 int 0.15mm EXH 0.3
#2 0.15mm EXH 0.5
#3 0.20mm EXH 0.45
#4 0.25mm EXH 0.45

Cant remember what the EXH stood for but they were each adjusted 0.10mm

Also, after 500miles of mostly highway use i used almost a 1/4 quart of oil and got 40mpg. Low mpg out of nowhere but i was also running around 75mph and seemed to be revved up. Despite the amount of oil loss i think it might have actually been worse so after another 1000 or so on full 20w-50 i will check again.

CoolAirVw · « **Reply #11 on:** November 27, 2007, 07:52:02 pm »

Exhaust

vanagonturbo · « **Reply #12 on:** November 27, 2007, 08:32:06 pm »

That would explain your compression drop in #1. The exhaust valve adj is way too tight. Its possible that the valve is being held slightly open to allow compression gasses to escape and lower the reading. Get that valve adjustment done.

The oil consuption is quite possibly a whole different problem. Hopefully nothing serious like rings and such.

The other thing to consider is that the term "rebuild" is used so loosely it probably should be regarded as "oil change". Especially when it comes to those buying/selling cars. I have heard of people using the most rediculous things as support of a "rebuild" to make a sale. so, unless you know the shop that did the "rebuild" pretty well or they have a good reputation then I would doubt what the seller told you in the beginning when you bought the car. Just food for thought...

TD_Bunny · « **Reply #13 on:** November 27, 2007, 10:32:08 pm »

yeah i have pretty much been eating crow since the day i got the rabbit lol. As far as adjustment goes the shop did 0.1mm adjustment and the results i posted were before they did anything. A short list, honestly the short one, of repairs is tranny, clutch(x2 as the first one mailed to me was the wrong size and i past the return date), rebuilt turbo, giles pump, all new hoses, scirocco 365 rad fan, shocks/struts.....any yeah ya get the picture. I am practically past the point of no return so now i am just trying to fix it. If I could do it over i would have had the engine comp. tested right away with the rebuild claim. Thing is, I have a 12k mile warranty written in stone for the engine but that just expired lol go figure.

When I get caught back up financially after christmas i will have a leak down test done to see what might be going on. Ill keep the post updated though if i notice improvements with oil consumption and such. later

burn_your_money · « **Reply #14 on:** November 28, 2007, 09:15:43 am »

with the car running take off the oil filler cap. If you don't have a cam splash guard you'll have oil spraying everywhere. Good idea to add one if you don't have one. If you have puffing white smoke (a lot of it) it's probably rings.