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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 31st December 2007, 18:39
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Default Engine rebuild 2.5 to 2.8 ltrs

Due to the car being off the road because of the broken wish bone we decided it would be a good idea to tackle the engine rebuild. This was more planned for next winter but never mind!

The current engine had 111k on it, and with the zone chip started running really well so we were not expecting any major issues. Part of the rebuild will involve dropping an M52B28 crank shaft and M20B20 conrods into the block. This will make it a square engine with an increase in capacity to 2.8ltrs. Further the head will receive a new set of performance valve springs and a dbilas 282/272 camshaft. All gaskets and seals are also being replaced.

Head off!


Inspection of the head reveals its in prett y good condition!

Nice tip for getting the bolt out the end of the cam shaft. Put the old timing belt around it, then loop the open end of the belt round the work mate. This locks it in place and allows the easy removal of he botl!

Rocker number out, shaft on its way out

Camshaft and everything else removed from head minus the valves

First valve out, couldn't take any more out as the valve spring clamp we bought was not big enough, needs to go back for the more expensive one!

The water pump was shot, all the bearings gone so that's why I had a bit of a funny noise from the engine.

More to follow!
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  #2  
Old 31st December 2007, 20:18
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This will be an interesting thread. From what I've experienced of the M20 engines, I like them - good solid engineering. I helped a friend sort his 325 when the HG failed (classic headbolt failure), and everything on the engine appeared to be in very good condition, despite 140k.
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  #3  
Old 1st January 2008, 16:43
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Everything so far on this engine looks pretty good too, exhaust valve are starting to pit a tiny bit and need a grind.

Rather than buying a new valve spring compressor we decided to make an extension for the current one.

After lathing the tube to the correct size with a suitable amount taken out the inside to fit over the clamp it needed holes in the side so that you can still remove the collets after compressing the springs:
The completed adapter attached:

And now in use on the head to remove the valves. Looking at this it would seem that it would have been possible to use it without the extension but it would seems to be easier this way up!

The intake valves and valve seats look great, but the exhaust seats and valves need re-grinding. They are just starting to pit. All in all everything seems to be in very good condition.

All the valves, springs and collets arranged in order waiting to be cleaned up.

The head could do with a dip, it seems to be nice and straight but I think I'll find a machine shop to double check everything for me!
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  #4  
Old 2nd January 2008, 20:43
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Quote:
Originally Posted by Patrick View Post
Due to the car being off the road because of the broken wish bone we decided it would be a good idea to tackle the engine rebuild. This was more planned for next winter but never mind!
The engine rebuild looks fun.
The quality of the BMW parts is just amazing and i'm surprised more kit designers are not using BMW donors? (A BMW Seven or BMW Atom would be great fun with M series engines )

Are your getting you body painted while the car is off the road?

Any news back from Marlin on the wishbone front?

br

Peter
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  #5  
Old 2nd January 2008, 21:40
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Originally Posted by peterux View Post
The engine rebuild looks fun.
The quality of the BMW parts is just amazing and i'm surprised more kit designers are not using BMW donors? (A BMW Seven or BMW Atom would be great fun with M series engines )

Are your getting you body painted while the car is off the road?

Any news back from Marlin on the wishbone front?

br

Peter
I saw some e-type replicas with M20's at Stoneleigh. Not sure what those were as I've never seen e-types before in kit form.

I think there is a BMW based cobra (which didn't get a glowing review in BMW car mag) and I'm sure I've see at least one other chassis with an M50 or M52 pictured in total kit car at some point.

On the non-kit side of things Wiesmann use the 6 cylinder M power unit one of their cars as well as the M62 8 cylinder in another.

Not getting it painted yet, I want more on road shake down time before everything gets coated.

I've boxed up the parts to go back to Marlin, didn't bother sending over xmas. Now I'm having trouble finding a courier company that will send the box. One half won't send to PO box address and the other half say their postcode doesn't exist!

A reminder of the bits going in the engine:












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  #6  
Old 3rd January 2008, 19:28
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Richard took the head to a local machine shop today, its booked in for crack testing initially before any work it done on it. Should be done by Tuesday!

Also got some "Just Orange" degreaser from Cromwell.co.uk:
http://www.cromwell.co.uk/SOL7272800A 1ltr
http://www.cromwell.co.uk/SOL7272810B 5ltr

Supposed to be some of the best degreaser there is! Had a bit of a start on the first set of valves. The exhaust ones are really badly caked, intake not so bad! Just orange, ultrasonic cleaner and a brass wire brush are cleaning up the rockers nicely!
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  #7  
Old 3rd January 2008, 20:35
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Quote:
Originally Posted by Patrick View Post
II've boxed up the parts to go back to Marlin, didn't bother sending over xmas. Now I'm having trouble finding a courier company that will send the box. One half won't send to PO box address and the other half say their postcode doesn't exist!

]
hmmmmmmm... Streetmap doesn't recognise their new postcode either but if you search for Marlin Cars on the Royal Mail website you get this.........
http://postcode.royalmail.com/portal...&gear=postcode
Map and all!

I suspect it is a new site and postcode.
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  #8  
Old 3rd January 2008, 20:38
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No courier company I called today would ship to a PO box address, so I'm going to have to split the boxes and send two via Royal mail!
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  #9  
Old 3rd January 2008, 20:48
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On second thoughts, having just read this post
http://www.madabout-kitcars.com/foru...?t=1471&page=2
it might be better to wait until February at least or your box of bits will be sitting in pile of mud!
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  #10  
Old 3rd January 2008, 21:04
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good point... gives us time to get the engine running
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  #11  
Old 6th January 2008, 18:14
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The head is off to the local machine shop for crack testing, we'll know if everything is good on Tuesday. If it is then it'll get a bit of clean up.

Clean valves! This took a lot of time! The exhaust vales were cakes. Used the technique from Jason's thread (thanks, a great idea ) placed the valve in drill and used increasingly finer sand paper to take the layers off and then some metal polish to finish it. The intake valves just need a run over with 1200 grit & some degreaser, then metal polish.
This was a 4 hour process with two people and two drills so about 8 work hours to clean them up! Some of them still have a bit of carbon build up but its very small and they still need to be run throug the ultrasonic cleaner and degreaser!

The tops of the valves where cleaned like the bottom half, the centres took a bit more work with sand paper and the edge of a knif blade. The only area left alone was valve seating area, that will be ground in when the head comes back from the machine shop.

Rest of the engine is out of the Sportster, looking a bit empty now.

Engine and gearbox out!

The clutch coming off

Sump off!

6 pistons removed from the block and numbered. They need a good clean and the conrods swapping for the 130mm M20B20 ones. I'm going to check the M52B28 conrods and the M50B25 ones I've got knocking about as well see if there's anything more suitable.

Bores in the block look great!

Flywheel off, had to lock the crankshaft in place with a metal bar between piston 3 and 4 then the bolts came out really easy!

Crank bolt came out really easy - surprisingly!
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  #12  
Old 6th January 2008, 20:33
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Quote:
Originally Posted by Patrick View Post
Clean valves! This took a lot of time! The exhaust vales were cakes. Used the technique from Jason's thread (thanks, a great idea )
You're welcome!

It's a mucky but very satisfying job, isn't it.
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  #13  
Old 6th January 2008, 20:42
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You're welcome!

It's a mucky but very satisfying job, isn't it.
Indeed they are all shiny now, a lot of work but really worth it! I found using a knife blade on the exhaust valves initially was a good way to get rid of the really bad grey/white stuff, and into the dip in the middle of the valves.
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Old 7th January 2008, 20:00
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M52B28 crank shaft sitting in the M20 block - this end will need some kind of spacer for the oil seal.



Crank sits in the block like it was meant to be there, runs round without any clearance issues - only other thing that needs to be tested is the M20B20 130mm conrod with the M20B25 pistons in place to check clearances.



One more picture for good measure!



One question, how the h*** to do you the cam belt pulley off the crank? It seems to be wedge solid. The cam chain pulley came right off the M52 crank so I assume its the same with the M20 except I've got 20 years of gunk keeping it on!

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Old 7th January 2008, 20:31
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I don't think I had many problems with mine, but it was a while ago... have you tried a three leg puller on it?



failing that, lay the old crank back in the block whilst you still have the old bearings in (so you don't bugger up the new ones). Put the mass damper pulley back on and bolt it up to the sprocket. Then use a rubber mallet on the back of the damper, turning the crank a little each blow until you work it loose.
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Old 7th January 2008, 20:49
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Not tried a puller yet, I've got one in the bottom draw. Will give that a go next time I'm in the garage - just wanted to make sure there wasn't a pin holding it in somewhere before I try the brute force approach! Thanks
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Old 8th January 2008, 12:16
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Hello Patrick

It looks like you are not going for a rebore then? If not, you must be really careful that there isn't a step worn in the bores at the top of the piston ring travel. Even the slightest step is a problem. What happens is, if you replace your piston rings or mess about with the stroke, there is a danger that the first time you run the engine the new rings hit the step. At best they will break dropping bits of piston ring everywhere IN the engine. Not good when it is running.

If you are using the old rings it is not a problem as there will be a corresponding step worn in the ring which will fit the step in the bore. Unless you are changing the crankshaft throw of course....

Also, if you change the rings you must get the bores honed or the new rings will not bed in properly.

Just my 5 penneth worth....

Good luck!

Robin
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  #18  
Old 8th January 2008, 13:07
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Thanks Robin Plan is to use the existing piston rings if they are within spec. Otherwise I'll get the bores honed. In theory the pistons should come up and hit the same spot as the old ones. I plan on dropping a single one in initially to check clearances and distances. The above pictures are just a test fit as I need order new shells.
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Old 8th January 2008, 13:48
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Quote:
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Thanks Robin In theory the pistons should come up and hit the same spot as the old ones.
If that's the case it seems an easy way to get a few more CC's!! Once I am complete and SVA'd I am thinking about fitting a Megasquirt. I used to be an electronics engineer (In the days that transistors were little round things with three legs and chips were something you ate LOL) so it looks an interesting option to me.

Now if you had those extra CC's and a Megasquirt - hmmmmmmm

Robin
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Old 8th January 2008, 13:52
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Originally Posted by MartinClan View Post
If that's the case it seems an easy way to get a few more CC's!! Once I am complete and SVA'd I am thinking about fitting a Megasquirt. I used to be an electronics engineer (In the days that transistors were little round things with three legs and chips were something you ate LOL) so it looks an interesting option to me.

Now if you had those extra CC's and a Megasquirt - hmmmmmmm

Robin
Megasquirt is on the cards, drop the AFM (barn door as the American's call it), distrocap and rotor arm and run wasted spark
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