[gigem75]

This is not a trick question. Which way should one rotate the crank to take up the lower chain slack? Approach TDC rotating clockwise or anti clockwise and stop at TDC? It makes a difference where the cam marks end up, at least on my motor even though the lower chain is low hours. Thanks

 

[super1750]

I'd say in the same direction the crank turns when it is running - clockwise.
Cheers
Bob

 

[gigem75]

Thanks, that's what I thought but then I started thinking about it

 

[alfaparticle]

Clockwise for setting the valve timing and both directions to check valve to piston clearance.

 

[super1750]

Good point Ed!
I've never thought to check the clearance in both directions but wouldn't the clearance be greater counter-clockwise due to reversing the slack?

Sorry, brain fart: Theoretically it would have to be smaller....

Regards
Bob

 

[alfaparticle]

I think that you get more clearance on the intake and less on the exhaust when the engine is on the over-run.

 

[super1750]

Jeez, and how am I supposed to get to sleep tonight with that unsolved puzzle? :wink2:
Just kidding but I'll definately check that next weekend.

Bob

 

[alfaparticle]

I may have got it backwards. At TDC the intake valve is opening and the exhaust valve is closing. Turning the crankshaft backwards wrt the camshafts to put the chain slack on the other side will mean that the intake valve is less open and the exhaust valve is more open.

 

[Clayton105]

I am jsut starting to rebuild an engine for a friend/client. The odd thing was that it had a lot of slack in the lower chain that belied the wear in the liners/state of the rest of the engine.

It was initially just going to be a reseal/headwork, but the it appears at some time the engine sat with water in #4 pot, and has etched the bore... Hence it has sort of expanded into a bigger job.

Initial pull down has shown that the engine has been align-honed. Crank is higher in the bock and is causing much more slack in the lower chaing than normal (even for higher mileagle engine.

I will be installing a lower timing chain tensioner in this one to combat any issues from this.

 

[gigem75]

Please post photos of the tensioner.

 

[Clayton105]

Please post photos of the tensioner.

Will do when the tensioner is mounted. It is from a Jag/MG. Topic has been covered here before.

I made a comparison to another block last night. This one has the crank 0.3 mm higher. No wonder the chain was flapping in the breeze.

It also explains why compression was so high when I tested it. ~ 200 PSI... The head had been shaved 0.7 to 111.1, therefore the pistons protrude 1mm more into the combustion chamber. My guess is 10.5:1 comp.

I have only ever seen one other Alfa 4 pot block line honed. That was on one that had had a holed block and had been welded. I have no history on this engine apart from it is in a 1750 GTV that was a bit of a bitsa before it came my way.

With line boring, one only takes a whisker out of the block.

 

[quadrifolio]

you wont be able to use that tensioner in the pic, its a hidraulic one and you wont be able to "feed" it, you need one with a spring in it, I´m in the same scenario with a 1.6 block

 

[PSk]

Will do when the tensioner is mounted. It is from a Jag/MG. Topic has been covered here before.

I made a comparison to another block last night. This one has the crank 0.3 mm higher. No wonder the chain was flapping in the breeze.

It also explains why compression was so high when I tested it. ~ 200 PSI... The head had been shaved 0.7 to 111.1, therefore the pistons protrude 1mm more into the combustion chamber. My guess is 10.5:1 comp.

I have only ever seen one other Alfa 4 pot block line honed. That was on one that had had a holed block and had been welded. I have no history on this engine apart from it is in a 1750 GTV that was a bit of a bitsa before it came my way.

With line boring, one only takes a whisker out of the block.

All you have to do is reposition the idle pulley the same amount higher ... or install your tensioner, but is it the best option?

Machine the idler shaft bearing bosses out and press in an interference fit alloy plug, remachine the idler shaft bearing bosses in the new higher position. A good machinest could do this in a day. The top chain will have more slack but that can be adjusted out.

Nothing is impossible to fix.
Pete
ps: if my block needs to be line bored, it will be as I want to save the block and having a true and correct block is the only starting point.

Has anybody worked out how much shorter and therefore lighter you could make the conrods, if any at all, because with this block design you could just machine the block and liners shorter to compensate. If I was building a full race engine I would investigate this because when you order rods you can specify any dimensions you need. I also believe the rod angle is a lot less than a Sud engine so as long as you can design the pistons so they clear the crank the shorter rods will be fine. Also as a bonus the resulting engine will be lighter.

 

[Clayton105]

picture time.

Couple more timings to do before final wash and reassembly. But this is the scuzzy MGB timing chain tensioner in place.

After thinking about it and working out how it works, I came to the conclusion that the oil feel is primarily for lubrication of the chain in the MG (shudder). You see, the only other lubrication the chain would actually see would be oil from the front cam journal (therefore a more positive supply is required. An Alfa has oil literally pouring down from above all the time. There is spring to push the tensioner out somewhat and a non return mechanism in this tensioner that prevents it from being pushed back in. However, the spring is not overly strong and the oil feed may assist somewhat. I could have drilled the block and supplied the oil to the tensioner, but I don't really think it needs it and would prefer to have the oil at the bottom end. I have installed a stronger spring in the tensioner and machined a stop for the tensioner at the new base loading setting.

A little work on the timing case is required to clear the tensioner.

22 beer tickets for the tensioner and 2 hours work.

 

[Alfar7]

tensioner

commonly a new chain does not have that much slack and what is shown is likely from intermediate sprocket droop.

If there is a little backwar movement room in the unit, then when the front cover is attached you should be ok. Otherwise there might be too much tension on the block & tensioner.
There is a allen head device to set and release the tensionerin the bottom hole. As with the Montreal you cant get to it, but you should leave a bit of room and let it set itself I would think.

 

[spinta volante]

TR4 chain tensioner in alfa

http://www.alfabb.com/bb/forums/engine-rebuilding/187073-lower-chain-tensioner-slack-line-bore.html

 

[Curtis]

Is this for noise? Or why is the tensioner needed?? I had a race engine like this. The load side tensions itself and is not slack enough to skip. Just made sure everything cleared on overrun and everything was fine.

 

[PSk]

Is this for noise? Or why is the tensioner needed?? I had a race engine like this. The load side tensions itself and is not slack enough to skip. Just made sure everything cleared on overrun and everything was fine.

On the over run (when engine is decelerating) if the lower chain is loose the valve timing alters considerably, while not a power issue could be a valve to piston issue (maybe).
Pete

 

[Clayton105]

To tell the truth, in this case it probably was not really necessary. The engine is standard apart from the porting work I am going to do while it is apart. I never really noticed any significant noise from the front of the engine.

Whether it will reduce wear on the chain I can only guess....

It mainly because I am fussy and its not how it should be... I did have a spare 1.8 engine/block that I was going to give to him, but when I went to pull the head it would not budge... I spent and hour and pushed it outside into the "to be taken to the tip" pile.

 

[Alfar7]

Chain slack

On the over run (when engine is decelerating) if the lower chain is loose the valve timing alters considerably, while not a power issue could be a valve to piston issue (maybe).

Absolutely in a race motor with proper clearances (close).
That`s why my instructions for determining correct usable LCs includes measuring cam to piston clearance while turning the engine backwards.

Saves $$ and tears!