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wayne1978trucks

3.5 v8 8.13:1 compression test

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hi guys i have got hold of a rough running 3.5 v8 110 van dirt cheap, (misfires until warm then will tickover high but has NO PULL whatsoever and dies) we want to put our 1985 one ten csw back to a standard v8 so don't want 3.9 4.0 4.6 etc etc just a standard 3.5 on carbs....anyhow we did a compression test and 6 bores were about 110psi and 2 bores were 105psi on a dry test but didn't have throttle down.

I have searched every where to see if these figures are ok on a low comp engine but come up with no definite answer, also the chap claims that its got 3.9 cams in, does this effect the comp test?

if I have missed a thread with all this in please redirect me....thanks

wayne 

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Hi, in short 3.9 cams shouldnt affect the compression ratios as the cylinder swept volume remains the same and valves should still be closed on the conpression stroke, i believe the 3.9 cams either gave more valve lift than a 3.5 cam or held the valves open a slightly longer duration as the larger engine could digest more air and fuel, (there are probably people on here who can talk in far more detail about it) but if you get more air in the cylinders you can tune the carbs to throw more fuel in thus more power for pennies if you had to replace a cam anyway.

The two cylinders that are lower than the other 6..... are they next to each other in the block? If so suspect head gasket leaking between them possibly.

and rough running, not to teach you to suck eggs but a genuin dissy roater cap and leads can cure all sorts of evils, and if the engine were scap you can put these on a different unit easily so not money lost.

company called RPI have lots of usefull info on thier website if you fancy a look, may turn up your desired pressures for compression test.

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perfect thanks flash, no the 2 lower readings were on opposite banks, ill do a proper wet and dry test when I get 5 and really work some numbers out.

on the dizzy etc the chap before me had put in a new dizzy, leads and coil before he parked it but I noticed as we were removing each lead to see which one was missing some were sending a real crack of a spark and others were less of a crack as though some leads are weaker.

rpi very informative

wayne

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If you want ignition related components the place to go to is.

http://www.simonbbc.com

From memory of when I had a 3.9 cam in my 3.5 it gives a small increase in power. Something to do with the increased valve overlap.

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neil'l90 thanks guys 

neil yes I have researched simonbbc as well as rpi and after this weekend (doing compression tests and leak down) ill consider the purchase of other offending items 

l90 yes that's what has confused me whether 135 is for my compression is a mystery however I also think mine is fitted with a composite gasket so without a headskim that also makes for lower compression....so the investigation continues...

and before I get 'why did you buy that?' , ive paid as much as a rolling chassis/body only so once the engine and box are in the garage the rolling vehicle can recoup the outlay, plus the engine is as sweet as a nut...no smoke...no tappet cam or big end rattles, very clean, no oil leaks, clean inside plus a gungy looking sd1 v8 engine thrown in for nowt and an lpg kit with tank so even if its scrap its only cost me time and 

thanks again chaps

wayne

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You are quite right, a comp gasket will lower the CR a little but is worth it IMO. As for the spluttering and cutting out, have you set the mixture and timing properly? I’ve had Rough idle when cold because of a blocked vacuum pipe from the dizzy before. Does it run for longer with the choke out?

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I'd be wary of RPI, general consensus on the internet is that they will often flog you a Mallory distributor whether you need one or not. 

Try v8tuner or v8developments for parts and advice, they get much better reviews from people!

Before spending loads of cash check through all the basics. High idle could be badly set carbs, or an air leak. Having no power could be lean mixture, which again *could* be related to an airleak. 

Doug's suggestion on seeing what the choke does is a good one. 

The misfire while it's warming up, is it a light miss or more like it's running a few cylinders down? Can you pinpoint if it's a specific cylinder/s? 

 

 

 

 

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Many years ago I had a 3.5 that missed like that, and I could never sort, no matter what I tried with fuel or ignition. Turned out one of the cam lobes was so worn it was barely opening number 7 inlet valve. I bet if I had compression tested it, it would have read less than the rest. Whip the inlet off and have a look - the cam gives you a really good indicator of V8 health. 

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Steer clear of RPI (rip off pisstaking idiots) very good salesman but known for selling stuff you do not need at an inflated price, that said, the website is a pretty good source of info.

 

hadnt even thought of vacuum leaks, spray a little wd40 around the inlet/carbs/manifold while the engine is running. You’ll soon find the leak if there is one

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Sorry for the long awaited reply,

not done anything to it, the wife has got me finishing the kitchen and the 300tdi is in the garage getting some love and attention.

thanks for the advice, done the wd40 test already.

 tried to run it with a little tweak of the carbs as directed (told to lean it slightly after the lift test on the needles) now the miss is light when cold with slight choke on then gets worse as it warms up with no choke, choke out when warm makes it rev it conkers off, the miss is now a lot worse under load (can drive it cold, wont pull of the drive when hot)

 

started with the basics ...ordering all the service items due to following...found a plug lead broke (pulled of the plug and left the end on the plug), checked and found carb balance awfull, which led to finding that it has the throttle linkage attached wrong, so got hold of a workshop manual and now going through all the basics

coil/module duff... seemed to put out less spark the warmer it got.

not check vac unit but its on my list

After the above I had a chat with a friend that builds aston martin v8s and rebuilds su carbs on aston martin db's and he offered to check the carbs out and do a refurb if needed, he will set them to default while I set about checking compression again, leakdown test, all vac hoses, throttle link replacement, service items inc coil, leads, module etc.

how do I check the cams with inlet off?

see you in 6 months lol

ps I used to get a ping on my email when I got a reply to a post but its not happening how do I get it working again(it partially why ive taken so long to reply)

 

thanks again wayne

 

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No worries :) worth taking a peek for the sake of a valley gasket, make sure you're not flogging a dead horse. 

Keep us posted on what you find - always interesting. 

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hi folks just a question about air filters as I'm going through this thing putting things back to how they should be the air filter should be a huge can behind the carbs attached to the elbows with 2 filter elements in (605191) 1 at either end.... does anyone know what this part number is for the steel casing as ive gone through all my parts catalogues and found nothing.

i think quagmire used a p6 one but is that the same as the one I'm after?

 

thanks wayne 

 

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The P6 one is round in cross section, the Range rovers had one very similar but flatter and more oval shaped in cross section - the paper filter elements are the same as far as i know.

Proper carbed Defender v8's have the carbs connected to a metal t-piece that then connects to a huge dustbin sized filter which only has a single outlet on the clean side. 

 

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I might have a spare dustbin filter if you need, last I looked they were insane money on eBay for some reason so I've hoarded a couple when I found them cheap - no idea  why really as they won't fit either of my V8's now they're EFI :rolleyes:

RPi's website is useful for basic tech but they still think 4-barrel carbs and Mallory dizzies are a good idea and oh BOY do they want to sell you expensive stuff you don't need!

You are on the right track doing all the basics by the book, just for the love of all that is holy use GENUINE parts, especially IGNITION bits - Rover V8 ignition is weak even as standard, non-gen parts (even half-decent ones) can kill it dead or at the very least have you chasing your tail. Even the wrong set of (brand new) spark plugs can lead to it not starting.

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thanks Quagmire and Fridge, not had much chance to do much as ive now got the other 300tdi in the garage, however my father and I were resetting carbs and fitting new genuine ignition parts and noticed a carb butterfly screw missing so that's on the list...and the accelerator cable had been direct fitted to the lh carb which dosent give it full throttle oh and burlen fuels have identified the carbs as hif6 not 44, if the carbs were old and knackered i'd be getting recon hif44s but the carbs are like new in and out

as for the filter I've seen the defender carbed dustbin air filter but I don't think that was fitted to my 1985 one ten, ive got a pic of the type that was originally on it (the pic is not mine its off ebay)....am I going in the right direction? as I thought mine had the two paper filters in each end with each end being removable.

s-l1600.jpg

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That looks like a P6 filter can sure enough - here's the one that used to be on my P6 for comparison (it's been EFI'd for a while):

5a2a597a9a8ca_Wiring-intoEngineBay1.thumb.JPG.e64f597f31fe393e894b5ffacc521707.JPG

Never had any issues with running the same setup on my 90 either. 

Edited by Quagmire
Get the damn image to work

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Quagmire, I thought that, but a p6 dealer pointed out that the p6 intake pipe is smaller than that one I showed in the pic, when I was scouring the internet world I got the impression that the light blue air box in my previous post was fitted on stage 1 v8's, and that with mine being early it may of been what was fitted to it in the factory.

You know when you did things decades ago that you thought would improve things that you later regret....that's where I'm at now eg no pics of her when I bought her and many of the original items got rid off over the years......stupid boy!

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