Car shakes on accelerating

[samuelm]

Hi all,

I have a 1968 Herald 13/60 that's giving me a little bit of trouble. The car runs nicely from cold, starts easily every time and seems to have plenty of power to zip around.

Once the engine is warmed up (and the choke is all the way in) when accelerating from a stop in first gear the engine shudders/shakes/vibrates quite severely. It's very disconcerting. Once the car is moving it stops, and has no problem under load at higher RPMs.

Has anyone here had similar issues or have any clues as to what might be the cause?

I'd think the correlation to temperature rules out universal joint or clutch issues.

Anyone have thoughts on what to check?

• Timing too far advanced
• Air hose/vacuum leak
• Lean carb? Detonation/pre-ignition due to lean carb not adjusted properly (was the herald 13/60 fitted with a temperature compensator?)

Cheers

[glang]

It does sound like weak mixture to me and you could check this by giving some choke when it starts doing it. If it improves you pretty much confirmed the problem....

[thescrapman]

Sounds like clutch or engine mounts to me.

everything stops shaking as the load is removed.

[RobPearce]

It's also worth asking about your driving style. Do you let the clutch up at very low revs? Or open the throttle a bit then feather the clutch in? Are you used to a modern Citroen where you have to take your foot fully off the clutch before it engages?

[samuelm]

Thanks for all the suggestions.

glang, I'll have a play around with the choke and see if the choke being out on a warm engine makes the issue go away. The strange thing is that once the engine has come up to operating temp just enough to push the choke back in (after about 5 minutes driving) theres no accelerating problems still, not until I've been driving for 30 mins or so and it's really warmed up does it start to show, and seems to get worse the longer I've been driving. So it does seem related to temperature.

thescrapman, I thought about clutch or engine mounts, but figured that issues with the engine mounts would be pretty consistent, not sure how that would be effected by temperature/choke, like I said it seems to be run better immediately after I first start up the car. Would it make sense for the clutch to only exhibit these symptoms after the car is warmed up?

robpearce, I am definitely more used to modern cars, but am no stranger to classics either having driven a few before (alpha spider, chevy impala). The clutch in the herald bites very soon as you start to come off the clutch, and again, I can drive consistently and only experience the problem after 30 mins of driving. Once it starts playing up with a warmed up engine I can get the car rolling without the vibration by really pushing the revs and coming off the clutch incredibly gently but that's definitely not driving normally - feels like a good way to burn out the clutch.

Lastly, is there any way it could be connected to valve head recession? The car has low miles (only 50k) and genuinely spent most of it's life owned by an older lady, but the previous owner before me told me he just bought premium petrol and didn't bother with fuel additive which worried me a little. Anyone here have thoughts on fuel additive or cylinder head made for unleaded?

[RobPearce]

It's not VSR. The Triumph engine is pretty robust and has good "lead memory", so unless you're thrashing it the PO's use of premium petrol without additive should be fine. My GT6 has been driven without additive for most of the last 20 years, including four RBRRs, and shows no sign of VSR. Besides, the symptoms of VSR are loss of power and difficulty starting when cold.

[samuelm]

Thanks Rob, I had heard that fears of VSR are often exaggerated. Puts my mind at ease.

[PeteStupps]

Evening.

Clutch judder gets my vote. Maybe a tiny trace of grease on the flywheel, that starts slipping more as it gets hot. Worth having a good look at your engine mounts though, as they're a lot easier to change than the clutch!

Pete  

[samuelm]

Thanks Peter, pictures of engine mounts attached. To be totally honest I'm not sure what I'm looking for in terms of wear here. I would have thought if they were worn out they'd look more "dropped" but not familiar enough to really know. I guess they're cheap to change so couldn't hurt 🤷‍♂️

[glang]

The first engine mount could be a bit suspect. They always have cracks and splits and shouldnt be replaced for pattern parts lightly but that one needs to be tested by using a beefy lever of some sort to see if the rubber separates....

[ferny]

The first one looks like it's breaking apart and the second photo isn't detailed enough for me to tell. 

There should be no "sag" to the mount.

I became so fed up of replacement mounts failing - in one instance it broke in two within months - that I used solid engine mounts for a few years. 

[RobPearce]

I'm with Peter - the first looks like it's failing and the second, while hard to see any detail, looks like the inner steel part is offset from where it should be, which would indicate that it's already failed.

I had a brand new one fail like that on a car that had never even had the engine started since the mounts were fitted. The quality of those currently available is dismal.

Jack the engine up (put a plank of wood under the sump to spread the load) just enough to take the weight off the engine mounts. Don't try to lift the car by the engine but do expect it to move up on the suspension a bit as you take the weight. Watch the engine mounts as you do so. If the rubber separates, or if the metal bits seem to slide through the rubber at all, then you need to replace them.

[samuelm]

Thanks for the advice all. For what it’s worth even new mounts seem to have that “displaced” look to me but I’ll try some careful lifting of the engine and see if the steel part of the mount is moving through the rubber.

If I were to replace them, in terms of the dismal quality of what’s on the market does anyone have suggested brands? I was thinking of ordering these https://www.angclassiccarparts.co.uk/products/triumph-5981/herald/engine/engine-mounting-kit-herald-1200-1250-1360

[nang]

I think Australia were making good ones recently. Have a look at Greg Tunstell's site.

Tony.