Mk1 - Full engine dismantle

[camstevens]

Hi All
I finally took the advice (coming resoundingly from all angles) to completely disassemble and totally check the Mk1 engine. And I'm soooo pleased I did. Even though it has been rebored, new pistons and shaft ground in 2015, it was a mess.....and to be honest probably caught just in time. Eg, the new JP pistons were totally seized on all gudgeon bearings, camshaft and lifters all totally worn, etc, etc. Oil was filthy and it has clearly been thrashed.

I guess I just struggled to understand why one would spend a fair bit of money only to throw the balance of it back together with old junk ????
I guess the positive thing is that the core of the engine is otherwise pretty solid.

So, have spent my first tranche of ££ to restore things, but really feel it best to start from scratch with new sleeves and pistons. IPD provide a reasonably cost effective kit, but I have a couple if questions;
- how do the compare to JP?
- they come with a raised crown, which I understand gives a higher compression. I want to take it easier on the engine....is it best to machine off the raised dome on the piston? I assume the higher compression is not advisable on a somewhat delicate Mk1?
- if I remove the dome (as above), will this necessitate a rebalancing procedure (at least static)?
- am I asking questions that are "old hat"?

Cheers
Campbell

[paul.jameson]

Have you cleaned out the sludge traps? If not, expect all your efforts to be wasted when the con rod goes through the crankcases.

[Knud.Degnbol]

Yes, that's the most important thing.

[camstevens]

Hi
If you are referring to the traps in the crankshaft, yes, that's definitely on the agenda. I imagine the siezed gudgeons were due to heat, lack of oil and dirty oil. Major scuffing on pistons, even though new in 2015.

Do anyone have any thoughts on the piston / sleeve questions?

Cheers
Campbell

[Steven.Carter]

I've only good things to say about IMD pistons that I've fitted to my hunmaster

[Simon.Gardiner]

Cam:
If you've not found them already, a few refs to IMD pistons in Square 4's....
http://forum.arielownersmcc.com/viewt ... 99&p=45809
http://forum.arielownersmcc.com/viewt ... 81&p=41607
http://forum.arielownersmcc.com/viewt ... 77&p=41159
http://forum.arielownersmcc.com/viewt ... 65&p=38397

SG

[camstevens]

Thanks Simon
That was super helpful.
I'm inclined to go with IMD pistons and liners, but take the crowns down. The question is "his much", but taking them right down makes sense. General consensus is that lighter is better w.r.t. balance / vibration, but static balancing at least advisable.

Cheers
Cam

[david.anderson]

From what I understand the imd is a fairly light piston. I doubt that you can remove much from the crown. A thin 1mm compression plate under the cylinder may give the desired result.
The use of an otto head gasket will also reduce compression a little as it is a little thicker than a copper head gasket and if the engine has a lot of miles on it valve seat recession will also reduce the compression ratio.
With regards to balance, the balance factor is zero as the crankshaft is 1 up and 1 down. Provided the pistons (and conrods) on the one crankshaft are the same weight there should not be a problem. All the square 4 cranks that I have checked (except for one in my 4 which had been altered by a previous owner) were in perfect static balance.
With regards to the seized gudgeon, are you saying the gudgeon was seized in the little end bush.
The use of a modern oil not specifically meant for a vintage engine can result in rapid wear of the cam and followers. So it is possible that the cam and followers were in good condition when the engine was rebuilt. Use only quality high zinc oils.
David

[paul.jameson]

A couple of years ago I spoke to the man behind IMD pistons at the Stafford Show and said I regretted that he didn't do the low compression variant. His reply was that he had left plenty of meat on the piston crown so that they can be machined down to reduce the compression ratio. I may yet have to do this for my 1936 4G but at present I am putting up with occasional clouds of smoke.

[Brian.Fosh]

Hi,

I wanted to use a dished set of NOS dished Pistons in my MK1, probably intended for a cast-iron 4G but Drags liners proved exact size for IMD std pistons with only enough extra metal for honing, and alas around 3-4 though thou too big for my dished pistons.

So I went for the IMD pistons in a hurry to get the bike built. They actually work fine ( very impressed in fact. Burns about half a coke can of oil in 1000 miles) BUT starting does need a firm kick and probably not usual for a SQ4..It is easier now at 3000 miles and starting is 1st or 2nd kick when warm. Carb jetting can remain as normal. I also needed much cooler plugs B8HS to cope with an even hotter running head.

On balance, I would rather have had turned the tops down.

I do use a thicker base gasket. Drags are only paper thin so I thought to fit 3 gaskets, but instead I bought some thick gasket paper on ebay, stuck one of drags on that and then cut out. I do this not so much to compensate for the very high compression but more to compensate for the skimmed head and and barrels that compounded the problem.

Even the club rods were tight on both the NOS and the IMD gudgeon pins. I actually reamed my small-ends so that they were only free running when warmed to just hot enough to still handle (around 60 deg C)


Regards, Brian