Thread: How to compression test a 300tdi

Hi Deano, I don't know how much I missed out by as i used the minimum measurements you gave me (.81 mm and .86 mm) and didnt look to see how much I missed by. Now I know I get an extra .1 mm with the thicker gasket (no holes on tab), I will check and see if .71 mm and .76 mm feeler gauges fit. Is that correct??

If they don't measure up, do i use the other head or do I have other choices? See ya mate

if the valves are standing too far proud have the seats cut back and the valves cut back to suit.

theres a few different cuts you can work in but remeber its oiler with its heritage back in the 70's just run with the stock 3 face cut.

cut it nearer the face of the valve with a narrow seat if your going to rev it hard

cut it nearer the stem and wider if your going to go slower and labour it.

may also be worth K lining the stems while your getting te work done.

I am working on that answer Dave. I will get back to ya after I do the 5 year TAFE course on advanced auto engineering hahahahahaha. Only being a smart ass mate I will talk to the local diesel engineer. I will be able to impress the guy and he will think I know something even though I am almost clueless. Maybe he wont overcharge me with a lot of luck. Any idea of a 'roughy' as to the costs to do this please Dave. Thank you - Gerry

Hi again Gerry, What Dave's talking about in detail is what we talked about back in post 33.


Here's a pic.






The blue arrow shows the valve seat surface that the valve seals to. The red arrow shows the valve sealing surface.


By removing the valve and grinding either or both surfaces the valve will sit further down into the head which will increase the valve head stand down.


Dave's reply refers to the different ways of grinding the valve/valve seat to optimise performance. Not particularly relevant to a 300 tdi and as Dave said just go with a standard cut.


Any competent head re conditioner will be able to achieve this for you given the correct stand down figures. The only limitation here would be if the valve head/seat needed to be ground so much that they became too thin. Hence my question re what is the actual stand down figure at present.


With a bit of luck you're going to have a pretty good head by the time you've finished. ( Either that or it's been machined too far and you'll have to toss it. )


Deano


PS. Don't give up yet and remember you've still got the rocker pedestals to shim which is not a big deal as it's not an overhead cam engine where it's critical to get the cam journals perfect. Ask you head reconditioner, he may be able to sort this as well.

Thanks Deano. I understand at last. I will try and get those actual stand down figures today. I am not at home as I have been doing work for Mum these past 2 days. She is 83 and just moved into a Nursing Home. I am trying to make her comfortable with some of her own furnishings, TV and organizing the phone and Internet connection etc etc

Hi guys, can anyone tell me the firing order of the 300 tdi (1342 or 1324) and is number one cylinder the one closest the radiator? Thank you Gerry

Good morning Deano. I have those valve stand down figures.
Starting from the thermostat end:

.75mm(Ex) .74mm(In) .73mm(In) .88mm(Ex) .88mm(Ex) .75mm(In) .74mm(In) .73mm(Ex)

Disaster or recoverable??
Thank you - Gerry

Hi Gerry, firstly firing order is 1 3 4 2 with no 1 at the front (radiator end) of the engine. Cylinders count 1 2 3 4 from front to rear.


Well, there's been a fair swag machined off this head. The 20 thou. sounds about right as including this would put the no.1 & 4 exhaust valve stand downs in the middle of the allowed range. Though it could have been skimmed previously.



In the order given the measurements are below minimum by


11 - 7 - 8 - OK - OK - 6 - 7 - 13 thou.


The variation is about what I'd expect end to end with the most material being shaved from the ends of the head (as it warps 'up' in the middle) to make it flat again.


With a zero hole gasket (4 thou thicker) you will effectively end up with


7 - 3 - 4 - OK - OK - 2 - 3 - 9 thou.


Which are at least single figures.


If it were mine (and I didn't have a spare head) I'd have the head reconditioner grind 5 thou out of all the inlet valve seats and as much as he could safely take out of no1 and 4 exhaust valve seats up to a max of 10 though and put it all back with a zero hole gasket and hope for the best. .
I'd also have him grind the rocker pedestal pads which will be out of level by a similar amount so that the rocker gear will go back OK.


The are several down sides here with the major one being increased compression in no1 and no 4 cylinders on an already high compression (diesel) engine and the effect this will have on other engine components. If it were a petrol engine it wouldn't matter a bugger. And the issue of whether the head is soft (the engine not you )to start with.


The other consideration is cost, how much do you want to spend on an already damaged head . Are you bit of a gambler.


On the other hand if I had a spare head that wasn't bent like a pretzel and had **** loads machined off it I'd use this as my starting point, even if I had to spend money on it at least I'd end up with an expensive good head as opposed to an expensive buggered one.


Any of that make any sense




Deano