3.5 v8 dies after 10 mins

Have you tried running it without those filters on after it starts running problems?...

Shippers said:

Have you tried running it without those filters on after it starts running problems?...

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I think so I will try again anyway

Muddy goose said:

Hello mate yes as a new complete rebuild
Tight big ends? What was that oil starvation and over heating?

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I bought the Cresta from a mechanical idiot who had a friend who was also a mechanical idiot but willing to have a go. I didn't know it at the time but these two had replaced the big ends and had put the wrong size shells in. It was a 6 cylinder, No 1 big end seized and scored the crank. I replaced the remaining 5 big ends, removed No1 piston and con rod and carried on driving it. On tick over it shook like someone with Parkinsons on roller skates.

Col

Right she started quite well this morning and only stopped a few times while warming up. Once idling I took of the air filters it dropped in revs slightly. Looking at the carbs left hand carb nearside the chamber doesn’t look like it closes down as much as the other side, also a little stiffer to lift and when I lift the chamber it goes to stall then picks up again. The right hand carb chamber shuts quite quickly and when I lifted it not much happened to the tick over. Checked coil and just warm to the touch.
Didn’t take it for a test run as noticed the charge light didn’t come on and battery not charging on tick over so didn’t check fuel in carbs on shut down. Just another kick in the ass cos I need it ‍

the piston should have some resistance when you lift it up, and snap down quickly when you let it go. when the engine is off, you should be able to lift to the point you can't see it and it should be a nice smooth action.
if on idle, one piston is holding higher than another, then your carbs are not balanced. if its that noticeable then you need to sort it before proceeding any further. the left hand carb is obviously way too lean, while the right hand is not far off
I think you're getting closer to the resolution

Thank

kermit_rr said:

the piston should have some resistance when you lift it up, and snap down quickly when you let it go. when the engine is off, you should be able to lift to the point you can't see it and it should be a nice smooth action.
if on idle, one piston is holding higher than another, then your carbs are not balanced. if its that noticeable then you need to sort it before proceeding any further. the left hand carb is obviously way too lean, while the right hand is not far off
I think you're getting closer to the resolution

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Yes it is stiffer to push up and for it to come down on the left hand carb

that should be an easy fix take the plunger out, lift the piston up as you take the cover off and you should be able to take the lot off without spilling any oil
be careful of the spring inside and of the needle under the piston!
dont forget to check the alignment groove in the piston, might be full of crap

while you're at it, clean out all the old oil in case one has a different weight to the other one

Well they did get recleaned and checked a few weeks back I will do another clean no crap in it last time but chamber still slow on dropping down? What oil do people use in the dash pots?

Muddy goose said:

Well they did get recleaned and checked a few weeks back I will do another clean no crap in it last time but chamber still slow on dropping down? What oil do people use in the dash pots?

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does it move freely and quickly with the plunger removed? the plunger itself might need a clean
you're supposed to use a special oil I believe, but I have always used regular 20/50 engine oil and never had any issue

kermit_rr said:

does it move freely and quickly with the plunger removed? the plunger itself might need a clean
you're supposed to use a special oil I believe, but I have always used regular 20/50 engine oil and never had any issue

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Hi yes it does move quickly with the plunger removed. The right hand carb makes a little clunk noise when it re seats the left is slower and doesn’t.
I’m going to see if I can track down a SU carb man

never had to touch a plunger, but i would have thought a good soak/agitation in some diesel or paraffin might sort it out. someone else might know better

Muddy goose said:

I’m going to see if I can track down a SU carb man

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Why?
Seems @kermit_rr is pretty clued up in being able to explain. ( something I sometimes struggle with)
Have you had a gooogle as loads on setting up SUs mg forums is a good source.

I got these

If I ever come across another with SUs.
But the Crypton is handy for setting up the Zed.

Even badly set if the run, they run. Still for some reason doesn’t (for me)explain the cutting out totally.

Do you have a gravity feed container you could rig up to supply fuel for testing purpose.

J

Have you got jubblie clips on all them fuel lines?
Unsure where some of them pipes go from the earlier photo.

marjon said:

Why?
Seems @kermit_rr is pretty clued up in being able to explain. ( something I sometimes struggle with)
Have you had a gooogle as loads on setting up SUs mg forums is a good source.

I got these
View attachment 181854 View attachment 181855
If I ever come across another with SUs.
But the Crypton is handy for setting up the Zed.

Even badly set if the run, they run. Still for some reason doesn’t (for me)explain the cutting out totally.

Do you have a gravity feed container you could rig up to supply fuel for testing purpose.

J

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whats that tool set for? looks exciting!

to get the balancing in the ballpark, a feeler gauge is a good start
i made my own vacuum gauge to set more accurately. works well on my bike and cost about £5

kermit_rr said:

whats that tool set for? looks exciting!

to get the balancing in the ballpark, a feeler gauge is a good start
i made my own vacuum gauge to set more accurately. works well on my bike and cost about £5

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The kit is for all the little adjustments that are hard to get at does Stombergs and SUs note the little spanner for SU it’s Churchill good stuff. Plenty of kits on the bay (not much money but not Churchill.
They are Old hand me downs from Dads garage. I used it quiet a bit when I used to tinker on a Saturday. And setup the twins on a cooper s engine I had just rebuilt, scary moment.

If I have all the carbs off the bike yes would agree feelers is a good start. But when on the bike vac gauge works a treat for checks.

Will I ever use it again? Probably not but it’s staying in my tool chest

J

Muddy goose said:

Hi yes it does move quickly with the plunger removed. The right hand carb makes a little clunk noise when it re seats the left is slower and doesn’t.
I’m going to see if I can track down a SU carb man

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That clunk that you describe is what they call snap in rebuild threads...in my zeniths if the needle is to far screwed in it jams the piston and slows it down preventing it snapping back down completely but not sure about su...at idle with filters off you lift the piston with a fine blade and listen for a change in idle and adjist mixture to suit of correct idle should rise slightly and then settle back...but if your piston is not snapping back down there is a problem there...

Right I have tracked down an SU specialist and he’s booked to come down next Wednesday so fingers crossed it is the carbs and I get it sorted it would be nice to drive her this summer as I finished rebuilding it last September!
Thank you again for everyone’s help so far you’ve all been a great help

Any news did su guy help...