question Hotchkiss Jeep engine help please with advice on engine problem

[Healey75]

Over the years I've restored many classic cars and know my way around engines, however this one has got me stumped... it's a c1957 Hotchkiss Jeep and the engine has gone sick, I've carried out a compression check on all cylinders and it gave 85 to 90psi on all cylinders which is where I'd expect the compression to be BUT with the engine running it's on only 3 cylinders (I've checked out the spark plugs and all good and working) and with the carb intake pipe removed is pumping back through the carb and you can see a spray of fuel pulsing out. This suggests to me a stuck inlet valve but all cylinders have compression on the test! Also there's a loud metallic clattering which rises with engine speed but does not get much louder but I can't isolate where it is but could be the cam follower/tappet rattling against a stuck open valve...but again the compression test suggest the valves are ok... unless one valve is only sometimes sticking but I'd expect it to clear or stick in one position.

 

The only other thought I've had, that there's some sort of air valve/flap on the manifolds between the exhaust and inlet manifolds, which I've not seen before, its got a counter weighted lever on a spindle and this is free to move and jumps about with the engine running... could something have rusted through and I'm getting exhaust blow back through the inlet manifold or is this valve just a blow back/flame trap device on the inlet manifold?

 

The engine oil looks ok although there's lots of emulsion in the filler neck as the Jeep sits mostly on display in the Wings Museum at Handcross so rarely gets a long run, the radiator water looks clear which suggests to me the cylinder head gasket is ok especially with the compression check result.

 

So there you have it, I'd appreciate any feedback or ideas as to what could be the problem, I don't want to tear the engine down until I've some idea of what the problem is...wait to hear guys, thanks

[GeePig]

I have no idea what engine you have, but if it is an OHV can you run it without the rocker cover. Second, have you pulled the leads off the spark plugs, one by one, to see what difference that makes?

 

And - what is it like inside the distributor? Nothing loose?

 

trevor

[Healey75]

I have no idea what engine you have, but if it is an OHV can you run it without the rocker cover. Second, have you pulled the leads off the spark plugs, one by one, to see what difference that makes?

 

And - what is it like inside the distributor? Nothing loose?

 

trevor

 

Thanks Trevor, couple of good thoughts there, it's a 4 cyl side valve so the tappets are buried behind the manifolds, I'll try pulling the plug leads in turn to see if it's just one cylinder playing up and check the dizzy...maybe that's the rattle, but with all the plugs out and connected they all have bright sparkes as they should but then I still can't reconcile that with the blowing back through the carb (it's not back firing or spitting flames back) just blowing back on what seems one cyl....

[commander]

Sounds like a valve seat has come loose to me or a broken valve spring

Commander

[Pete Ashby]

Before you start to strip down the engine I would suggest putting a vacuum gauge onto the PCV port to see what inlet manifold depression you have. If everything is doing what it should expect anything from 17 to 20 inches with only minor flicking. Let us know the result.

 

Pete

[mtskull]

I have seen an engine (admittedly a more modern one) show good compression on all four cylinders under a cranking compression test but which, when started, would only run on three. I followed my instinct and took the head off and the problem turned out to be due to a partially failed head gasket which would hold the cranking pressure but not the combustion pressure.

[Nick Johns]

 

The only other thought I've had, that there's some sort of air valve/flap on the manifolds between the exhaust and inlet manifolds, which I've not seen before, its got a counter weighted lever on a spindle and this is free to move and jumps about with the engine running... could something have rusted through and I'm getting exhaust blow back through the inlet manifold or is this valve just a blow back/flame trap device on the inlet manifold

That is the "hot spot" device for directing hot air onto the inlet manifold to prevent the carb icing in cold weather, nothing goes wrong with it so this will not be any thing to do with the problem,

As Commander said I would suspect broken valve spring or a valve seat has come lose in the block, or there is something loose in the inlet manifold, at cranking speed it has compression. but when running something is keeping a valve open.

I had very similar symptons with a Dodge engine, turned out someone had dropped the air cleaner wing nut down the carb and it occasionally got jammed under an inlet valve keeping it open, thus the engine was missing on one cylinder, accompanied by loud tappet clattering and blowing back through the carb, the only answer is to remove cylinder head and check all the valves, seats & springs and check nothing is floating around in the inlet manifold

Edited April 6, 2014 by Nick Johns

[Healey75]

That is the "hot spot" device for directing hot air onto the inlet manifold to prevent the carb icing in cold weather, nothing goes wrong with it so this will not be any thing to do with the problem,

As Commander said I would suspect broken valve spring or a valve seat has come lose in the block, or there is something loose in the inlet manifold, at cranking speed it has compression. but when running something is keeping a valve open.

I had very similar symptons with a Dodge engine, turned out someone had dropped the air cleaner wing nut down the carb and it occasionally got jammed under an inlet valve keeping it open, thus the engine was missing on one cylinder, accompanied by loud tappet clattering and blowing back through the carb, the only answer is to remove cylinder head and check all the valves, seats & springs and check nothing is floating around in the inlet manifold

 

 

Thanks everyone for suggestions and info, looks like it must be a valve or head gasket, since the water and engine oil look ok, I'll start with removing the valve chest covers and see if there's a broken spring and go from there, looks like the head will have to come off as well in due course....

It'll take me a few days but I'll post up what I find. If I can borrow a vac gauge I'll run that test as well.

Cheers, & thanks again.

[Pete Ashby]

I can see that you know your way around an engine so I hope you don't think I'm telling you how to suck eggs but do the vacuum test first it will help you to diagnose where the problem lies :-).

Gauges are on ebay next day delivery for under £15, don't go for fancy oil damped ones you need to see the quick response to determine whats going on, for those who are interested and haven't used one before Google 'tuning using a vacuum gauge' there are plenty of good sites that will clearly explain what the different types of response are telling you .

 

regards

 

Pete

[Ian L]

Sounds like a valve seat has come loose to me or a broken valve spring

Commander

 

2 Summers ago at W&P one of our group had exactly the same problem with his Jeep engine, I quickly pinned it down to which cylinder was at fault but he didn't want to go any further at the show.

Once back home and the head was taken off it was found to have a loose/broken valve seat, same as Commander said.

[Healey75]

2 Summers ago at W&P one of our group had exactly the same problem with his Jeep engine, I quickly pinned it down to which cylinder was at fault but he didn't want to go any further at the show.

Once back home and the head was taken off it was found to have a loose/broken valve seat, same as Commander said.

 

Quick update... see attached photo, broken valve spring on no 5 exhaust vavle, I'm missing one collett so will drop the sump, hopefully it's made it's way safely down to the bottom

[GeePig]

Well, that is the advantage of a sidevalve engine, the valve doesn't drop onto the piston

 

Glad to see you have found the problem!

 

trevor

[Healey75]

Well, that is the advantage of a sidevalve engine, the valve doesn't drop onto the piston

 

Glad to see you have found the problem!

 

trevor

Further update...maybe of interest to others... It looks as if there was a reason for the valve spring failing on the Jeep, the last person to put the valves in was the monkey rather than the organ grinder! When I took the sump off to look for the missing valve collet which had made it's way there, I cleaned out 50 years of sludge and found another collet that had been there a lot longer as it was embedded deep in the sludge and gunge I scraped out.

Have a look at the attached picture (it's taken with a mirror as the problem is hard to see otherwise) the valve on the right is correctly installed with the collets flush in the spring retainer, the middle and left hand valves have the collets incorrectly installed the ones nearest the camera are actually in upside down, the collets are tapered and you can clearly see how the spring retainer is not secured properly....

 

This could mean that some enthusiastic rpm's could shake the collets out, the valve spring is under additional compression since it has not been able to extend out to its working position which will over stress the spring, also there's a good chance the spring is going to be coil bound when the valve opens, again not good. Any one or a combination of these could cause the spring to fail.

 

I was going to replace all the springs anyway as a precaution but this makes it essential since the extra valve collet found in the sump is just that, so it may be that another spring has dropped a collet in a past incident... at least there's a spare collet now!