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Go Back   Madabout Kitcars Forum > Mad Build Area > Marlin Sportster, Cabrio, Berlinetta and Roadster builds

Marlin Sportster, Cabrio, Berlinetta and Roadster builds Enthused or Confused about your vintage Marlin build? Ask away here or show off your build.

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  #1  
Old 3rd October 2015, 16:22
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Default Another Sportster's (finally) on the road!

The Sportster has her plates so I took her out for the first drive this afternoon.




I only went a few miles for the first trip just to get a feel for it. It seems to be pulling well but I need to sort a few problems out, the main one being a significant vibration at 50+. I had the front wheels balanced this morning ahead of the drive as I'd knocked all the weights off when I had my steering rack issues. The vibration is coming through the body rather than just the steering so next stop is the rears. I know that there's a very minor buckle in one of the rear wheels but shouldn't be enough to create so much vibration but it will be my first port of call. I'm just hoping it's not an issue with either the prop-shaft balance or angle between the gear box and diff.

I still have the suspension set up for the IVA test so I've got quite a bit of toe out plus the tyres are pumped right up and the suspension is all on the softest settings so addressing these things may help a bit. I've also got the new 40mm spacers on the rear so I'll see if I can run it without just to eliminate them from the equation.

My front cycle wings still bounce around quite a bit even with the extra reinforcement I fitted but I can see a fix for that already. Generally the car seems very squeaky/rattly but as I've never owned a car like this, it may just be noises I never normally hear cocooned in the cabin (I get obsessed with finding even the tiniest squeak in my cars).

I think the length of the nose is going to take some getting used to too. I was a bit paranoid about clipping the curb as you have to lean your head around to see where the wheel is. That will become second nature after a short time though.

If anyone's got some good advice on suspension settings for the road, I'd be interested. I'm going to change to a spot of toe in on the front and generally lift the ride height all round to make it a bit more speed bump friendly. It's the amount of damping front and rear I'm not too sure on from the point of view of the bias.
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Old 3rd October 2015, 19:21
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Dear Ian,
firstly, a big congratulations on finishing your car and getting it registered! I bet your first drive was exciting and that view down the bonnet is something to savour!!
I think you'll get used to the front mudguards bouncing around which, so long as they don't fall off, is quite normal and nothing to worry about.
From memory I used to run with tyre pressures around 18-20 psi and only a couple of clicks from full softness on the front shocks.
I'm not sure about the vibration but perhaps you've flat spotted your tyres on your first lap (...well that's what they always say on F1 TV )

At least we finally know that gearbox works okay

Happy motoring.............peter.
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Old 3rd October 2015, 20:04
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hey that's a thought, maybe it's the gearbox causing the vibration
No, it works fine and changes are nice and smooth, well, provided I press the clutch down properly. It takes a strong left leg with the current setting.

I've basically worked out where the mid point of rebound setting is on both front and rear dampers and set to that now. I'm going to get a full day of testing in tomorrow so should be able to play around with things a bit.

One thing I did notice when I had the car jacked up is the front NS wheel has a slight buckle. I thought I'd put the dodgy one at the back deliberately as you'll notice it less there but now I'm wondering. Hopefully that's all it is and I've found the problem rather than I now have 2 buckled wheels

The other things I noticed on my test drive were that the oil temp never got really warm on the whole 6 mile round trip, maybe 50 degs. This may be because there's so much air flow round the sump or that 6 miles just isn't long enough.

I've also noticed that oil pressure isn't really getting very high on my gauge and the light blinks now and again. The oil level is good but I did add some of that tappet loosening stuff (can't remember the name) a year back when I had the VANOS rattle issues. The oil seems more like the consistency of veg oil than engine oil so I wonder if it's a bit thin. A change wouldn't hurt I think.
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Old 4th October 2015, 09:36
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Well done

Can you try the wheels from your daily driver on there see if tht cuts out the vibration? That is if the tyres on the rear ones will fit in the arches as the MV type 1's are staggered!
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Old 4th October 2015, 10:48
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If sorting the buckled wheels doesn't cure the problem I would suspect the prop shaft! Has it been apart or new parts been fitted? I once replaced just the front yoke on a Mk2 Cortina (splines semed a bit worn) but didn't have it re-balanced. At 50 mph the vibrtion was horrendous! Ended up refitting the old yoke which luckily I had identified and all was well again.

Also do a quick check that there aren't any dribbles of paint or underseal on the propshaft as that will be enough to throw it out of balance (as does repainting it!). Peter.
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Old 4th October 2015, 12:34
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The prop was a new custom made unit and had been balanced (had a little plate welded on). That doesn't mean it was correctly balanced mind you. I'm going to rule out all the more common causes first as that will be a pain to get looked at. I refurbished the drive shafts too so it's entirely possible they're out of balance though being so thin I would have thought it unlikely to cause a problem at road speeds.

I reset the toe in on the front this morning then gave my wheels an inspection for buckles. The one I knew about was on the back after all so that has to be addressed anyway. what I thought was a buckle on the front I now think is just a bit of corrosion damage on the bead which after they we're refurb'd shows as a minor inward dip as you spin the wheel. It isn't actually out of round.

I popped down kwikfit with my good spare wheel/worn tyre and my buckled wheel/good tyre to get them swapped over and they refused to do it. Said it's against company policy as they can't guarantee the work unless the tyre is brand new. Sounds to me more like they're only interested in helping if there's a tyre sale in it for them. Nowhere else is open today so I'll go to a local garage tomorrow and get them to do it. I can't just get a new tyre put on the good wheel as you can no longer buy the one I need to match the other side of the axle. It's pretty frustrating as it writes off an entire day of good weather and testing. I could probably fit my MV-1 front 225 wheels on the back of the Marlin but Patrick is right, they are a staggered set up with 255s on the back. A bit wide for the Marlin.

I've fixed up the front wings a bit too. I think the main problem is the weight of the GRP. Has anyone fitted Carbon fibre wings?

Last edited by morris; 4th October 2015 at 14:42..
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  #7  
Old 4th October 2015, 15:50
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I've been doing a bit of reading around propshaft vibrations and come to the conclusion that the M5X engine set up in the sportster really isn't going to help.
Take a look at this link

http://www.therangerstation.com/tech...onangles.shtml

There's a diagram about halfway down showing the correct way to install a propshaft in terms of angles between the gearbox and diff. The Sportster set up is the worst possible. The diff is true to the chassis but the engine/gearbox is at an angle meaning that at best you'll have and angle at one end but not at the other. In the worst case (which is what I think we have) there is an angle at both ends but most importantly they don't cancel each other out and the angles are different so by the time the rotation gets to the diff, it'll be accelerating and decelerating all over the place causing a massive vibration. This is just looking at the layout from above before you even take into account any difference in height or angle between the gearbox and diff.

I'm now determined to get the engine sitting straight even though we've been told before the car is designed this way. That's moved to the top of my winter projects list.
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Old 4th October 2015, 18:22
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That's an interesting link and worth following up BUT what do other Sportster owners think? Have they had similar issues? If not IMHO it has to be a simple fix unique to your car rather than an inherent design issue. I remember a tyre fitting chap, years ago, saying that wheel(s) out of balance always seemed to cause vibration at either 30mph or 50 mph, but no reason was forthcoming! Peter.
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Old 4th October 2015, 18:59
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I have never had any vibration issues. My wheels were new and the propshaft was custom made (dave mac).

Bearing in mind that the propshaft rotates at 3x the wheel speed - I would have expected a highish frequency vibration if that was theculprit. (Perhaps it is - you dont mention details...)

Wheel vibration should be quite rcognisable - I guess most of us have had that at one time or another.

How good a fit was the propshaft? On my car (E30 based) I had to reem out the centre hole so it was a good fit over the gearbox spigot. The spigot is used for centralisation on the E30 box.

Cheers Robin
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  #10  
Old 4th October 2015, 19:56
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I wonder if putting the car up on four axle stands and then 'driving' the car with and without the rear wheels would shed any light on the cause. (but do make sure it cannot drop off the stands!!)
I'm guessing that if it is propshaft induced it will still vibrate without the rear wheels fitted.

I know I joked about flat spotting your tyres but maybe if the car has been sitting on the old tyres for a long time then maybe they have deformed?

My bet is on your old wheels or tyres...........
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Old 4th October 2015, 21:05
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Quote:
Originally Posted by morris View Post
I'm now determined to get the engine sitting straight even though we've been told before the car is designed this way. That's moved to the top of my winter projects list.
Hi Ian,

Great news and many congratulation in getting the car legal. Lets hope we get a few more good days before the weather starts to really go down hill.

I had a prop shaft made for mine and I put a new set of wheels on the car and the set up, with the engine and gear box at an angle must be much the same as yours. I've had no vibration problems at all (just bought up 11,000 miles this weekend) so I wouldn't focus too much on getting the engine straight. I think I would be inclined to focus on the wheels first and if you could change them all out, or at least fronts and then rears its probably the first port of call, at least to eliminate them if nothing else.

Cheers

Nigel
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Old 4th October 2015, 22:11
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Yeah, I'm not going to dive straight in and start moving the engine around (there are too many things tightly fitted around it) but just feel that I should have followed my gut instinct back at the start of the build and made the engine fit in straight so this kind of thing wouldn't be on the cards. I'm planning an engine swap/stroker rebuild so that will be the time to make these kinds of alterations.

It wouldn't be the first time (by a long shot) that I've over thought a problem and won't be the last.

I know most vibration issues come down to wheel balance and then can be exacerbated by suspension play or worn bearings (both of which are new all round). Vibration always comes down to a rotating component in the end and as the wheels have the largest radius, they're the obvious first choice culprit. The suspect wheel is in the boot of my car ready to get it looked at tomorrow and hopefully that will sort it out.

I've spent a fortune over the years chasing down vibration issues on cars and it's always been balance or not putting my hand deep enough in my pocket when buying tyres in the first place. I never buy anything but premium tyres these days as you end up wasting money on inferior products and subsequent trouble shooting otherwise.

I did think about putting the car up on stands and running it at about 2500rpm in 5th which would be roughly the speed the issue occurs at. I'm always slightly scared of that though but it will be my next port of call if the wheels don't solve the problem.
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Old 4th October 2015, 22:14
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If you put it up on stands also put some wheels under it, they give a nice big surface area if theres an issue with the axle stands
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Old 5th October 2015, 18:20
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Looks like bad news for the moment.

I've just run the car with the back end on stands and with the rear wheels on or off, you get the bad vibration at around 40mph.

I left it running on idle in 5th and from what I can see of the prop past the exhaust, it didn't look that smooth. Maybe some run out around the slip joint area.

the good news is that the drive shafts didn't visually seem to be vibrating so the problem must be between the engine and the diff. There's a little vibration when rev-ing the engine through 1000-2000rpm but nothing to get worried about. It certainly doesn't cause the issue when reving through the range in neutral which I guess rules the flywheel and clutch out too. So I guess it can only be the gearbox, prop or diff. The former will be easy to rule out if I disconnect the front end of the prop though I'm pretty sure I tried that when I first got the engine running but before installing the prop and I would remember a vibration like this. I don't remember any vibration from the diff on my drive home after buying the donor either.

Tomorrow I'll get it a bit higher in the air so I can look underneath properly, maybe drop the exhaust and try and film it at the resonant point to see what's going on. I'm hoping it is something silly (but not funny) like a bolt working loose though I can't quite see how that would have happened so soon.

If the prop does look dodgy I guess it's easy enough to send it off and get it looked at.

Last edited by morris; 5th October 2015 at 18:24..
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Old 5th October 2015, 20:58
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Default U/Js

Have you checked the alignment of the Universal joints in your prop shaft?
If they are not matched to the exact spline you will get vibration - particularly since the input/output flages are not in the same plane.
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Old 5th October 2015, 21:47
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Hi Mike,

I've not checked the UJ alignment directly but I did look at some photos prior to fitting to see if this might be the issue. It certainly looks ok here



I think some filming running though the gears will help, hopefully I can get that done tomorrow evening. I think a check of all the bolts is also a logical next step.
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Old 8th October 2015, 08:52
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Have you found the cause ?
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Old 8th October 2015, 09:14
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Quote:
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Hi Mike,

.................... I think a check of all the bolts is also a logical next step.
Not just tight but are the bolts and nuts all identical? i.e. same length. Also as someone said earlier check that the flange inner shoulder and recess is a good snug fit and doing the centralising of the mating parts and not just relying on the bolt holes. Peter.
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Old 8th October 2015, 12:02
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I'm still looking into it. So far I've tested the following:
- rear wheels off
- spacers off
- discs off

The problem persists. When I had my first IVA test and the examiner ran the car up to 70 there did not appear to be any vibration visible, audible and he didn't mention feeling it (I would have as it's not bearable). That got me thinking about what had changed and I realised I had swapped the rear brakes over from my E46 since that point but at the second IVA, we only hit 25-30 round the yard. I was hoping that it was something to do with the brake swap. Unfortunately this turn out not to be the cause as even with the discs off, it still shakes.

Unbolting the drive shafts from the diff and then unbolting the prop from the gearbox output are next. The bolts are all tight and the same length. I did have to modify the heads on some but tested they were all within a gram before installing. The flanges do appear to be mated properly both ends and the UJs are aligned. The welded on weights on the prop are still intact and there's no evidence of physical contact with anything. I'm also suspicious of my gearbox mount but would think that would cause a clonk on acceleration or coming of the throttle quickly rather than a shaking.

I've found a test to rule out the flywheel or clutch so will try that too.

I'm a little worried that I've ruled out the engine too soon because it doesn't vibrate when just rev-ing freely. Could worn crank thrust bearings be a factor? Would rev-ing in neutral but with the clutch engaged rule that out? I'm thinking of the force down the crank when under load.

Last edited by morris; 8th October 2015 at 17:56.. Reason: Use of a phone instead of a PC causing terrible grammar
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Old 8th October 2015, 20:35
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Quote:
Originally Posted by Grey V8 Pete View Post
Also as someone said earlier check that the flange inner shoulder and recess is a good snug fit and doing the centralising of the mating parts and not just relying on the bolt holes. Peter.
Ditto.
I would remove and clean the mating surfaces both ends to make sure there is no paint trapped. I'd also check how snug the fit is of the rear centralising raised section which locates in the diff flange.
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