1963 C10 Chevrolet stovebolt 230 engine dead miss on 5-6

[Allthegearnoidea]

Have Been helping a friend today with installing his Chevrolet rebuilt engine. I’m not sure what he had done but think it was new pistons, rebore and crank. I believe the head had some new valve seats a year ago and has run on the current cylinders head. But not sure if it was skimmed

The engine was running a little rough and found a dead miss on 5-6. This is what I have tried so far.

Checked timing - looks good
Changed plugs
Changed plug leads.
Re-timed the engine to be rotate plug leads one along - no change missing still missing 5 and 6
It’s single manifold twin carbs. Swapped the cards around. No difference
Have confirmed 5-6 has spark. Ouch yes.
Adjusted rockers for tiny rattle. No difference.
It’s an electronic distributor with inbuilt coil pack, was working on engine. Previous

I think next thing to do is a compression and leak down test. Unfortunately I am working at my friends house so unfortunately did not have my test gear with me. But cannot hold finger over spark plug hole when spinning over engine.pressure blow finger away so there is some compression.


I have triple checked timing but once had a timing issue on a v8 where it was I think 60 degrees out but ran perfectly but with a dead miss on two cylinders.

Probably need to do the compression test just to rule it out and then maybe inlet vacuum. But probably not manifold as running perfectly on other cylinders.

Just looking for more ideas as I will have another look at it next weekend.

 

[armalites]

So I'm assuming what you are doing it taking the lead off cylinder 5,6 and it's making no difference to the engine note?

It's not something as simple 5-6 leads are round the wrong way?

 

[Shox Dr]

Firing sequence is cast into the exhaust manifold, if you are unsure.

Make sure dizzy is set right; set 1st cyl tdc, rotor should be pionting at 1st cyl. Gap 16-20thou. Inlets 8, ex 20. Plugs 35

 

[Allthegearnoidea]

Hi thanks for replies. I did not notice the firing order on the exhaust manifold but pretty sure I’m correct as it came from the original workshop manual for the 230 engine. This would also be correct to the stovebolt forum and various other web searches. I did not try swapping the plug leads but again I’m very sure I have the correct firing sequence. I have done some google searches and I think this would have come up before now if it’s was some other sequence.

Yes checked that rotor is at plug 1 for TDC 0 on the compression stroke. No points to adjust it’s a fancy electronic ignition with inbuilt coil pack. Functional before the rebuild.

I adjusted rockers with engine running so did not check the gap. Probably varies as they have hydraulic lifter anyway. But followed advice on stovebolt forum.

It was worthwhile asking. I’m just hoping it’s not a compression issue. But that’s the only think i have not checked yet

 

[Allthegearnoidea]

 

[Shox Dr]

Firing sequence is cast into the exhaust manifold, if you are unsure.

Make sure dizzy is set right; set 1st cyl tdc, rotor should be pionting at 1st cyl. Gap 16-20thou. Inlets 8, ex 20. Plugs 35

I see its a aftermarket header so unlikely to have the firing sequence. While I know the static specs, I’m currently trying to time mine at full distributor advance, with little success, the timing light is also intermittent (sorry to thread jack)

 

[Allthegearnoidea]

Well at least I’m not the only one struggling.

 

[Olderisbetter]

Is it a new cap and rotor arm, MY moggy gave me a nice zap on No4 lean but had poor running it turned out to be the dizzy cap had a issue on the No4 peg inside, A quick scratching at it and iw was like a thick layer of oxidized clag, It ran ok but have changed it to a better one.

 

[p0689109]

Is the distributor shaft concentric ie no play that is allowing it to wander. Does not need much to cause problems.

 

[Allthegearnoidea]

It’s running a modern electronics distributor. Probably less than a thousand miles running on it rotor arm looks ok. We have ordered a new cap and rotor arm for a spare. These were fine before the rebuild so not expecting an issue. I did re-time the engine to move the plugs along one on the cap and this made no difference. I guess I should stop speculating that before I do the compression test but I’m trying to convince myself of a silly mistake or easy solution.

The egine block and bottom end was rebuilt at a local engine shop. And we installed the cylinders head. This was overhauled last year with hard seats installation for unleaded..

I can see us taking the head off next weekend. I have a compression tester but have just ordered a compression leakdown tester, belt and braces.

The only other think is fuel pressure was not great on this engine. Have swapped the carbs over and reversed fuel pipes but know inprovement.


So and engine only needs 3 things

Fuel - probably
Ignition- yes
Compression - unknown

Sorry about the typos I don’t have the heart to battle with the predictive text tonight

Thanks Regards Chris

 

[octo0072000]

View attachment 140810 View attachment 140810 View attachment 140809

seal up the breather pipe from inlet manifold to rocker cover see if that makes a difference

 

[Allthegearnoidea]

Yes did that. No difference. But I was running engine without air filter so that could make a difference.

 

[octo0072000]

Try squirting a tin ofwd40 along the inlet manifold near 5/6 you may have a air leak if so revs should go up a bit as it runs on the wd40

 

[zeppelin builder]

tight tappets

 

[colnerov]

Have you tried keeping the ign leads more formally separated, it might be cross firing?

 

[Allthegearnoidea]

Tappets have been adjusted with engine running. Plug leads are new and hanging in free space. It’s annoying I could not do a compression test. Hopefully be going over this weekend to do this. If I can rule out the compression than I can investigate some of the stranger ones.

I did think it was fuel at one point, but I swapping the carbs and feed hoses would have shown that as an issue. Also tried pouring fuel down the carb adjacent to 5-6. The plugs are new and no sign of combustion products on 5 6 at all.

 

[p0689109]

Try new plugs in 5 and 6 as they might have got wetted and killed them, even new ones.

 

[octo0072000]

swop plugs 5/6 with 1/2 assuming you have checked you have a spark at 5/6
use old plug in lead hold against cyl-head run motor

 

[Allthegearnoidea]

An update. Running now damaged manifold gasket. Didn’t show up doing usual tests and wasn’t making any noises.

 

[armalites]

That sounds lovely, you'd never believe a damaged gasket could cause a dead miss unless it completely blocked the port, you'd understand a missfire