The engine is a newely put together standard D-jet 1,7 with NOS heads, new piston rings, bearings, cam (std), adjusters and lifters. The rest are original components.
The engine runs really great, car pulls off like never before. Compression is about 155psi. Oil pressure good.

Since I have higer valve noise from the cyl 1-2 head (most noticeable during warm up) I measured the valve cover surface temp just to see ift here was any difference.

The 1-2 side was warmer all the time, at hot engine some 10-15C (~20F) hotter.
Valve cover temp for cyl 1-2 side was about +100C (212F) when stopping.
Checked for oil in both covers/rockers just after stopping, because oil should have great impact on the cooling, it looked the same, wet but not flooding.
The flaps had just opened when I stopped so the termostate bellow works.
Valve clearance set to 0.04/0.06 I/O as recommended by the cam manufacturer.

What could make one side run hotter than the other in this case?


/Lars S

All tin in place? Tin plugs in place?
Heads are cooled by air, and airflow is best for the 1/2 bank. Make sure all the Tim is in and all the holes in the tin are covered and plugged.

Thanks,
yes tin and plugs are properly in place.
Since this is at not to high idle only I suspect the air distribution/spreading not being as good as when running at higher rpm, this could maby be a reason...

/Lars S

Is it possible that you installed the large air flapper wrong?

Not likely, I never removed the flaps from the shaft. I can feel about the same airstream under the cylinders on both sides.


/Lars S

I would expect the 1-2 side to have worse airflow because the air has to change directions rapidly before it goes over the cylinders.

Did you check compression ratio on ALL cylinders before assembly?
you might have smaller piston to head distance on one side creating more compression and more heat. This may happen if the case was align-bored off center a bit or the cylinder registers were machined not equally. You can add spaces under the cylinders to offset this, if that's the case.
I'm not sure that the compression reedy you've done can reflect this situation accurately.

If you have higher valve noise from one side i would think adjusting the valves again would be the place to start.

That could account for both the louder noise and hotter running

I have checked the valves again, they are on spec. The extra noise on cyl 1/2 side is during warm up, when hot they both are wery much normal.

Its like when starting cold both sides gives no noise at all, during warm up cyl 1/2 side has quite high noise and when hot it goes back to what I consider normal.

Any reflections on that?


/Lars S

I thought the consensus was that airflow was best on 1-2, resulting in the best cooling in the order: 2 - 1 - 4 - 3 ?

I would start simple and check the valves again, as others have mentioned. I know nothing about aftermarket cams, but .004 is under the factory specs for a 1.7. It should be 0.006 for both intake and exhaust. Note: you also wrote your clearance as 0.04 and 0.06. That zero makes a big difference, but I figured its probably a typo. Either way, loose is better than tight, and 0.004 leaves less wiggle room.

Sorry, that was just a typo should be 0.004/0.006.
(Yes with 0.04/0.06 there should have been some noticeable valve noise )


/Lars S

3-4 always runs hotter in my experience, because it is opposite the tangent of flow from the fan. Where and how are you measuring temps?

Used a digital contact thermometer with contact paste, my final readings I made at the center of the valve covers (since i thougt that being a comparable place) but the tendency was all over the heads.

As I wrote this was at rather low idle so i might do the test again after a real run.

/Lars S

Yup, thats where I knew I heard that. Glad Jake chimed in. 1 and 2 received better cooling by nature of direction of flow, so expected best cooling and lowest cylinder temps go 2-1-4-3. Right Jake?

In my cars with stock cooling I see a 40-70* F increase in temps between 1-2 bank and 3-4 bank with 3-4 always hotter. The location of the sensor and characteristics of the TC and gauge (temp compensated or not) makes a difference as well.

After checking the compression (being equal for both banks) ant then the cooling system which functioned just perfect with flaps and all I found the reason to why the heads had so different temperatures:

The idle was to low. I hate high idle (specially when valves are noisy) so I had sat it in the 700rpm range. After lifting it up to 900-1000 both heads are perfectly equal in temp.
I guess the reason is that the air distribution system is designed for best function at normal operation rpms. If you look at the fan cover the air to 1/2 side and 3/4 side is led off from the fan at the same point, the 1/2 bank has a far longer travel to reach the heads. (this may be relevant since the 3/4 side has also to feed the oil cooler). Also at low air velocity the distribution can be wery distorted, you never know where the air goes.

Glad I found it at last!

Set it back to 700 rpm
at 900 you are already into you timing advance curve.
at idle you should not be worried about a 20 degree temp difference. there is no load on the engine.

Zach

Yes, I will put it back to "normal" again, but isnt the factory recomendation 800-900rmp or...?


/Lars S

idle is 850 +/- 50. I would think there would be problems with setting it so low as 700, that it would cause a "flat spot" off idle if it doesn't start advancing right away, at that same figure 850 +/- 50. Low is nice though. -I would think hot oil pressure would be a problem idling at 700, but maybe not.

Yes, thats true, I have experienced a significant flat spot from take off when having it at 700rpm.

/Lars S

Have you really checked everything?

Have you checked your distributor cans and mechancial advance plates.

This is Djet........You shouldn't have a flat spot with everything set and working corredtly.

My comment is based on my experience with different mechanical advance curves and settings only, like how an 050 feels compared to a 009 compared to a properly set mallory with carbs.

My experience with low idle is that it takes longer to get to the rpm to release the clutch. My 050 felt so slow on account of that. Could be I'm thinking about it wrong. It does get delicate, the slower it turns, has to run smoother to do it. It's certainly hard with carbs to get a good balance.

Interesting, about the difference in distance from the fan outlets being the cause. With the outlets being different size already accounting for the extra needed for the cooler and the duct being larger, it might be thought of like a McDonald's straw, more all or nothing. It has always seemed to me the system works well within certain prescribed parameters, picturing the intersection of graph lines to be even when it is needed, so the less-than-normal idle speed seems it could be reason enough.

I can never say everything is checked working 100% but I have gone through the distributor OK. If I set the full advance to more than the std 27 (say 30) I can get rid of most of it. Also setting the idle higher makes it better.



Having the idle at 700 is not set correctly to factory spec...



/Lars S

Deleted , got it.