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Author Topic: V8 Repairs  (Read 4104 times)

V8 Repairs
on: July 20, 2008, 11:13:28 AM
Seeing as this isnt getting very far in the Waffle thread, I thought Id start one over here. Anyways, the engine in question is a Rover V8 3.5l, slightly old and corroded [its been running on saltwater cooling for a while now, its the engine in a jetboat]. Every year weve used it its taken a bit of tinkering, but has always started. This year though, nothing. The timing is corrrect [we set to what it says in the manual], the firing order is just so, all of the spark plugs are firing just after top dead centre, theres oil, fuel and valves opening when they should and it wont even cough. We would, if we could, just crank the engine on the starter motor until it fires, but the main bearing in the jet is on its way out.It was replaced a few years ago, but the screws holding the jet together had corroded away, so we had to weld the unit shut. I just need to know a quick fix that should get it fired up and hopefully get another year or two out of it.

The engine has been slightly modified by way of installing a four-chamber Holley racing carb and semi-racing cams. The jet unit is a Hamilton 2-stage flow jet from NZ.


edit: four of the valves werent doing quite what they should
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Re:V8 Repairs
Reply #1 on: July 20, 2008, 11:23:14 AM
have you checked the compression on the cylinders?
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V8 Repairs
Reply #2 on: July 20, 2008, 12:40:22 PM
take all the plugs out, pour a teaspoon of petrol down into each cilinder, put the plugs back in and try it again ;-)
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  • Offline Chris

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V8 Repairs
Reply #3 on: July 20, 2008, 12:46:48 PM
Is the fuel getting into the cylinders?

Is the air getting in OK?

obviously a petrol internal combustion engine needs air, fuel, compression and a spark to fire, so if its sparking and the air filter isnt blocked and fuel is getting in, then Id suspect the compression is out.
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V8 Repairs
Reply #4 on: July 20, 2008, 13:14:43 PM
Quote from: knighty
take all the plugs out, pour a teaspoon of petrol down into each cilinder, put the plugs back in and try it again ;-)


Tried that, it wouldnt cough so we held a match to the exhaust and had a 4ft flame shoot out of it

And as for Chris, 1) yes 2) yes

It could be the compression, but weve no way to find out. I think what were going to try is to remove the driveshaft and just keep cranking it for as long as the battery will let us or until we get it to cough. If that fails, well have to consider finding a way of sorting out the compression. As this boat is going to be with me on holiday, I wont have internet so ideas on fixing the compression will be much appreciated.
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V8 Repairs
Reply #5 on: July 20, 2008, 13:20:01 PM
Id re-check its sparking in the right order... you could always have it set so its sparking on the exhaust stroke instead of the compression stroke....

(this only really applies if youve had all the plugs out/disconected at the same time since last time it worked...)

plus id take out the prop shaft, then take a generator and a good battery charger with me ;)
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Re:V8 Repairs
Reply #6 on: July 20, 2008, 13:34:56 PM
Well, weve set the timing so it fires just after top dead centre [as is said in the manual], all vales closed, after the intake stroke. The valve timing is just so: we can hold a match to the exhaust while cranking and light the unburnt the petrol. Its just not firing. The spark plug are [i think] sparking properly, Id have to check that tho. But cant til saturday.
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V8 Repairs
Reply #7 on: July 20, 2008, 15:08:37 PM
if you can light the exhaust then Id say its defenatly a spark problem... even with next to zero compresion, the fuel should still be ignited...

Id re check for a spark, and re-check all the daft things, like you havent leaned on and pulled out the coil power etc... :-o
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Re:V8 Repairs
Reply #8 on: July 20, 2008, 15:57:17 PM
righty ho then

As always, keep the ideas coming for any possible faults and fixes. Ill take a list with me to try.
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  • Offline Mark

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Re:V8 Repairs
Reply #9 on: July 20, 2008, 16:07:43 PM
if its cranking and not firing but is sparking

are you getting a good spark?

check compression as above

what state is the carb in? When was the last time it was serviced

are the cams degreed to manufacturer spec - NOT oem spec

Is the starter good? If it wont turn fast enough it will never build enough compression to start

how old is the fuel?
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Re:V8 Repairs
Reply #10 on: July 20, 2008, 16:44:18 PM
1) dunno need to ckeck
2)will do
3)pretty good nick, didnt need servicing the last time we got someone qualified to look at it
4)no idea
5)probably not. Weve got a new one to try anyway.
6)god knows. Probably 12 months old. Used to be unleaded, we put enough additive in it to boost it to 5-star racing-quality
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Re:V8 Repairs
Reply #11 on: August 08, 2008, 16:40:37 PM
Right then, seeing as Im back off holiday, I might post the state of thise here engine.

First, we took the simple approach and attempted to remove the drive shaft from the flywheel and crank the engine til it coughs. We gave up on that approach when we snapped the only allen key that would fit [the end of it is still in the bolt]

Secondly, the rocker covers came off. The contents of said covers were...dodgy at best. The rockers themselves were corroded, and four had siezed. With a little tlc however, they were good as new.

Then we saw the state of what was underneath the rockers. Four of the cams had seized, and those four cams had caused their respective pushrods to bend into a z-shape.

So, after seeing the state of the heads we decidied they needed reconditioning. Hence the holley carb [still pristine], the offenhauser inlet manifold and both huge Nicson water-cooled exhaust manifolds had to come off. The first two came off all right, but the steel pins holding the nicsons on had corroded into the aluminium of the manifolds and block, effectively welding them together. Much levering and the aid of a large hammer solved that problem. Once the heads came off, we saw the state of the block [the 7th and 8th cylinders looked deceptively dodgy, but the gunk in em was just from last years backwash, the block was almost perfect underneath]. So, the heads have been sent off to be re-conditioned and the engine should be running by the end of the season. I will post pictures as soon as I can get then off my phone [lost the transfer cable, wont have a card reader til mid-week].
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  • Offline Mark

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Re:V8 Repairs
Reply #12 on: August 08, 2008, 21:58:26 PM
a compression test at the start may have avoided all the damage :/
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V8 Repairs
Reply #13 on: August 09, 2008, 01:48:40 AM
thats what you get for using a petrol engine in a boat :p
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Re:V8 Repairs
Reply #14 on: August 09, 2008, 12:29:21 PM
A compression test may have helped, but the first turn of the key this season knackered the pushrods. I think 17 years of rot took its toll slightly....and as for Knighty, a petrol engine was the best choice. A diesel engine wont chuck out all its torque and power at 5500 revs and last more than a season.
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