Compression, or not

[AJ]

I posted this on the fccuk so apologies for those who've already seen it. I rebuilt a 16vt and put it in a 145. I was never convinced it was quite running right at low revs, however after 2k it picked up and was smooth, like normal.

(rebuilt 16vt, fairly standard except lightened + balanced internals, 3 angle valves & seats, rebore with next size up from standard pistons & rings)

Thought I'd just do a compression check last night:


---Dry--Wet
1 | 80 | 79
2 | 0 | 0
3 | 140 | 145
4 | 110 | 130


I thought it ran quite well considering....


I'll start stripping it tonight to see if it's anything easily obvious, like a tappet.

[AlfaJack]

hope its simple mate!

Whats the difference between Dry and Wet test?

[AJ]

Dry = erm, dry, as it is.

Wet = pour ~5ml of oil down the plug hole and retest. The oil will help to improve the seal on the piston rings, so if pressure increases with a wet test the problem is more likely rings rather than valves.

I'm hoping it's valves/valve train related.

[AlfaJack]

I'm hoping it's valves/valve train related.

Ta

And, me too!

[Steve Webb]

From the look of those figures, and the wet/dry tests it looks like #1 valves are not seating fully, and #2 valves are not seating at all. Or maybe a prob with the head gasket between #1 and 2 and #2 valves not seating.
But definitely looks like a topend problem.

[AlfaJack]

You got new valves in there? All re-cut etc?

[AJ]

They were the old valves which were cut with 3 angles, and the seats cut accordingly. It wasn't a harsh cut that was done.

What should the cylinder compression be?

I'm a little concerned cyl 4 perked up a bit with the oil test.

[Steve Webb]

When you rebuilt the motor, what was new and what was used?

[AJ]

Top end, all used (except stem seals). Cams were good with no wear.

Bottom end - new: oversized pistons + rings, shells (standard size)
Used: Crank (no wear), rods

[AJ]

Does anyone know what the compression should be for the 16vt?

And should it be done hot or cold? I guess when it's hot it will read a little higher.

The engine ran much better when it's warm.

[AJ]

Thought I'd just check the valve clearances tonight:
The Fiat 16vt tech doc gives:
In: .40mm +/- .03mm (=14.5 thou to 16.9 thou, ideal=15.7 thou)
Ex: .50mm +/- .03mm (=18.5 thou to 20.8 thou, ideal=19.7 thou)

Which looks very similar to the Q4 tech data.

I got (measured in thou as I don't have any feeler gauges in mm yet):

Lobe|In|Ex
1|0|4
2|6|2
Compression: 80 psi

3|0|6
4|12|0
Compression: 0

5|6|4
6|16|4
Compression: 140

7|6|1
8|2|13
Compression: 110


A measurement of 0 means I couldn't get the smallest single gauge in there.

Guess who must have forgot to check the clearances when rushing the head back together a year ago or so. Where's the best place to get shims from? I'm going to need some very thin ones!

[AlfaJack]

Iv got a set of 16 shims - let me know what sizes you need - might be able to do something. I will take a pic of them so you can see all of the sizes I have.

[AJ]

Thanks Jack, I think I'm going to need a bit of a variety pack. I'll whip the cams out and see what is currently in each tappet, then I can get a headache trying to work out if I can swap them, and what I need.

Do you know what diameter they are?

[AlfaJack]

No, they just came out of a Q4 head - il check tomorrow

[cuore_sportivo_155]

are these the small shims placed on the valve directly, like with the old alfa 8v engines? these exist in 8 + 9 mm (TS is 8mm, twin cam i believe to be 9mm)

[AJ]

Not on the valve directly, they go between the cam lobe and the tappet:

These were the things I should have measured (and changed) :

[cuore_sportivo_155]

yeah, a bit like VW then...

[AJ]

Got the tool, had fun playing with it and got a couple of shims out, then noticed the 7th lobe on the inlet was worn by ~2mm
So whipped the belt off and took the cams out to finish the job.

Hunt for an inlet cam.... is it worth trying to hunt one of these sought after Tipo inlet cams?

[cuore_sportivo_155]

then you'd use the original inlet cam in the exhaust, so just shifting the problem

[AJ]

I thought you could use Tipo NA cam in the inlet and still the standard 16vt exhuast cam. Think I'll just order a new standard cam for the 16vt to get it running. Main concern is where the swarf has gone.

[cuore_sportivo_155]

from the head to the sump, through the oil pump into the filter... the overflow for the head goes straight to the sump, and after the pump the oil goes to the filter

[AJ]

Think I'll drop the sump to make sure it's clean, change the oil filter then flush the cooler. Fingers crossed it'll all be ok then...

[AlfaJack]

If you need shims, I have:

3.90 x1
3.95 x2
3.97 x2
4.00 x3
4.02 x1
4.07 x1
4.05 x2
4.10 x2
4.12 x2

[AJ]

Thanks Jack, that's where abouts my current shims are, I need ranges between 3.25 - 3.50 for exhaust, and guessing at inlet of 3.50 - 3.80 (based on old cam clearances)

[cuore_sportivo_155]

because of the cutting and porting the valves would logically sit higher... are the shims still available? if not your current shims could be grinded to the correct thickness at an engineering shop