2300 WOES

[griffonmark]

Does anyone know for certtain whether the valves hit the pistons when a camshaft seizes on a slant four? My Magnum handbook says not, but someone 'in the know' tells me the 1800 doesn't but the 2300 does. If contact does occur what damage does it do? Has anyone any personal experience of this?

Regards

Mark

[cossieviva]

its the 1800 that hits not the 2300 and thats from a good friend of mine from cornwall who worked on them from new when he worked for river side moters in leeds in the 60s/70s

[griffonmark]

Thanks for the info, I've put mine back together again and it won't run so I was praying it didn't need the head sorting. I'll see if I can check the compressions.

Mark

[droopsnoot]

When I had bent valves on the Sportshatch it was quite obvious once the valves were out of the head, you could see the stems weren't vertical when placed next to a straight one. But a compression test will tell you whether they're OK or not.

[griffonmark]

Thanks everyone for your help. I did a compression test and the comps ranged from 150 to 152 psi so I think I have a good bottom. After a lot of head scratching I did find the fault. The previous owner had put the dissy drive back 180 deg out. He then put the swopped the plug leads around. When I rebuilt the engine I put everything back by the book, ie rotor arm points to no 1 cylinder. I never thought to check the plug lead order! All I had to do was swop the leads around on the dissy cap, retime with a strobe and the engine fired first time. I can't believe how well the engine runs now. I thought it was fast before, but its even quicker now. The main faults I found were that the floor mounted accel pedal didn't travel fully as the linkage fouled the floor bracket. I've never had full throttle - but I have now. I've fitted twin carbs and advanced the ign further as I found the plastic cover timing marks were slightly out. The valve clearances are set properly so it was a good thing that the cam seized, it helped me find all the faults!

The valves on a 2300 do not hit the pistons at tickover. Several people have reported bent valves after cambelt failure but I can only assume their failures have been at high speed.

Regards

Mark

[Sid]

If the distance from the closed valve heads to piston crown (at TDC) is greater than the maximum cam lift, then the engine will
*definitely* not be damaged, regardless of engine speed at the point of failure.
Skimmed heads and high lift cams influence these dimensions adversely, so obviously need to be considered, but a stock 2300 is safe.

Even if an engine fails to have the above safety margin (1800?) there is still a chance of survival as it it perfectly possible that
when the cam stops, none of the valves will be fully open. If no valves are protuding far enough to hit the pistons then the engine
survives.
In this latter instance, engine speed can have an effect, as the cam might continue to rotate a couple of times after the belt
snaps, leading to a short period where valves are fully opening out of sync with piston movements. That is the period where
collision is most likely. Once the cam comes to rest it all depends how far the valves are left open. If none are at full lift then
engine might survive even on engines where the closed valve to piston distance is less than the full cam lift.

Sid



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[griffonmark]

Thanks for the info Sid. I'm not entirely convinced that speed has nothing to do with it when tolerances are close. I have seen engines that have failed thropugh over revving, one in particular was a Merc diesel engine where the pistons touched the carbon on the cylinder cylinder head and had an indentation from the exhaust brake valve. At high speeds maybe the valve could leave the cam, particularly if the springs are weak. Also the piston/little end/big end clearances may close slightly under extreme pressure as the piston reaches top dead centre and oil pressure is unable to cope.

What I do know for sure is that on my 2300 engine the valves do not touch the pistons at cranking speed, whilst other people report anecdotal evidence of valves hitting the pistons following cambelt failure. I'm picking a head up next week so I think I'll measure the gap between the valve and head face.

Regards

Mark

[Sid]

> At high speeds maybe the valve could leave the cam, particularly if the springs are weak.

Yes, but "valve float" can only occur while the cam belt is still intact, in which case the piston is half way down its stroke at
the point when the valve floats.
The valve will always be in back contact with the cam at TDC unless its stuck open due to spring breakage or stem seizure. There is
no realistic likelyhood of a piston ever hitting a floating valve.

> I have seen engines that have failed through over revving

Yes, that is common but has nothing to do with valves hitting pistons. If a valve hits a piston under such circumstances (on a
"non-interference" engine) then that is the result of some other breakage such as a valve spring or conrod, or valve stem seizure.

> piston/little end/big end clearances may close slightly under extreme pressure as the piston reaches top dead centre

We're talking about a tenth of a millimeter unless the bottom end is knackered. Unlikely to be the difference between hitting and
not. Less significant than carbon build up, but that's same at any speed.

> whilst other people report anecdotal evidence of valves hitting the pistons following cambelt failure

Excessive skimming of the head and fitting of high-lift cams introduces dimensions which could make the critical gap as much as 3mm
different. That could potentially make the difference between fully open valves hitting a piston or not.
Though are you sure this "anecdotal evidence" relates to the 2300, not the shallower 1800.

Sid



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[griffonmark]

Hi Sid, again

Your comments are great, I feel like I'm learning something. However, I have seen a number of engines that have been seriously over revved, mainly commercial diesels, ususally by the driver selecting the wrong gear. On one engine the valves clobbered the pistons with such force that the 3/4 inch thick pushrods were badly bent and the twin plate clutch sheared. Several of these engines were over revved with the driver's admission and 2 of them were logged as over revved by the ECU software. I don't recall these engines having broken springs, the over revving merely caused piston contact with the valves. Most of these engines were under manufacturer's warranty and unlikely to have been stripped prior to failure.

You refer to the slimmer 1800 engine. Does that have different valve to piston clearances? I was led to believe the cylinder heads were interchangeable, the 1800 head gasket shrinking the combustion chamber to retain compression ratio. I do get told a lot of myths though!

Regards

Mark

[Sid]

As far as I'm aware the overall combustion chamber depth is greater on the 2300 meaning that the valves are further away from the
pistons. Somebody correct me if I'm wrong as I've never worked on a 2300.

> On one engine the valves clobbered the pistons with such force that the
> 3/4 inch thick pushrods were badly bent and the twin plate clutch sheared

Valve float alone couldn't possibly cause that. In a "float" situation you've got *gaps* between the valvetrain components, so a
piston impact with a floating valve wouldn't compress the pushrod.
The destruction you've described could be:-
a) the result of a broken camchain or belt on an "interference" engine. i.e. one where the valves will hit the pistons if they're
left in a high-lift position when the piston approaches TDC (ford x-flow for example, which has a flat head face).
b) It could be that the valve float was so extreme the pushrod jumped out of its seat and jammed the valve open.
c) At extreme revs, the inertial forces in simply lifting the valve at that rate can became so great that the pushrod (or the
rocker) can simply bend or collapse under the strain. The consequences are that pushrods jump out of their guides with catastrophic
results.

...but going back to my original point, that being that if an engine is non-interference by design then this applies equally
throughout the working rev range and remains the case if the camshaft siezes or the belt brakes. Something else in the valvetrain
would have to break to change that situation.

With those destroyed engines you spoke of you're confusing "cause and effect" to some extend I think.
In any case it would be unwise to compare the high-inertia valvegear of a commercial diesel with that of an OHC car. To bounce the
valves on a Magnum you'd have to exceed 7000rpm and even then they'd get *nowhere* near the pistons.

Sid




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