Z900 A4 Engine rebuild yet again!

[Gray17]

Afternoon guys, well if youve read my last post on fuel leaking youll already know the story, but basically about a year ago i fully stripped the bike to restore it back to as it should be, part of this was an engine strip, which included New valve guides, exhaust valves and hardened seats for unleaded use, all new gaskets were used along with numerous other internals, cam guides etc, the bores looked and measured ok so re used existing pistons etc, but after a year and a half finally got it complete ready for summer riding. Alas didnt work out as id hoped. It still refused to run right, tried all sorts, re cleaned all carbs, complete new carb kits, had choke plungers seals replaced, spent a fortune and still it wouldnt run right. So in the end bought compression tester and it gave poor reading on 1 cylinder but spurious on 2 others, after all the work it then started smoking.
So bit the bullet and stripped engine for a 2nd time, barrells were entrusted to IMD pistons who have rebored them and supplied all new pistons, rings pins and circlips.
Well they arrived back today, checked everything and it all looks good to go. So thought before diving straight it id check if theres anything else i should do, ive got a new full gasket set, new engine oil, also bought a DS2 electronic ignition too as was having problems with my timing. So after all that hoping it goes back together well and runs as it should.
Any advice or suggestions welcome
Thanks

[warren3200gt]

Good luck Graham. IMD do a good job.
Gotta ask though who advised it needed hardened seats for unleaded use.?

[zed1015]

Good luck Graham. IMD do a good job.
Gotta ask though who advised it needed hardened seats for unleaded use.?

Unless the seats were knackered there was no need for replacements because hardened seats were already fitted from the factory and these engines were designed to run on unleaded from day one..

[warren3200gt]

Good luck Graham. IMD do a good job.
Gotta ask though who advised it needed hardened seats for unleaded use.?

Unless the seats were knackered there was no need for replacements because hardened seats were already fitted from the factory and these engines were designed to run on unleaded from day one..

I know Rob, that's why I was asking who advised to have them replaced.

[Gray17]

Thanks for replies,
No one actually suggested it, I took head in to engineering shop as valves guides very worn, they advised new guides and exhaust valves, inlets deemed to be ok, head pressure tested and skim. If you remember from my original post there were some hairline cracks on the seats ( advised thats normal by forum members) but was concerned about them spreading, they replaced them to solve this they also recut all valve seats at same time, oh and a protruding spark plug helicoil was removed and a timesert put in its place. Not really bothered why they were replaced now as its already done, need to move on and just get it running right, so hoping new pistons and rebore will sort that?

[r3sc]

Good luck with the rebuild!

When you stripped the motor did you find anything obvious with the bores or rings which could have caused the odd compression figures or is it looking like the head/valves are your main issue?

[Gray17]

Warren seems to think i may have measured it incorrectly.
I was taught to 1st use fingernail on top of bores to feel for ridge
(none present that I could feel), next using torch look into bores to check for damage, scoring or scratches ( again none present), then check pistons for damage, scoring, blowby marks or partial seizure marks (again none present) next take top ring off each piston insert into bore using piston to ensure parrallel near top then near bottom, measure gap with feeler gauge. This seemed OK too from memory, i deemed lower compression was therfore down to head rather then worn bores. However apparently bores may have had slight ovality whereby rings touch at multiple points but not seal? I can see Warrens point, as didnt check this(My Bad) but report from IMD was no ovality but slight wear on all bores. So Ovality wasnt the issue They have now been taken to 1st oversize. I will re check all valve seats before fitting head just in case though.

[warren3200gt]

Andrew wouldn't have bored them unless they were close or over the wear limit. He would have just honed them and supplied new rings. Whenever he does work for me he sends the existing measurements prior to discussing the way forward and moving onto boring.
What did he advise Graham?

[Gray17]

Hi Warren, he advised the bores were partly worn but not oval. But would benefit from a rebore hence thats now done.
Whilst its good questioning why, think that horse has long since bolted now, the fact is its now rebored and honed and everything will be as new, the question i raised was is there anything else i need to do before i start refitting them, bare in mind all cam guides etc, cylinder head, valves, stem seals, guides etc have already been done previously. Knowing what i know now, i probably should have done it the 1st time, problem is i didnt know what i know now, its been a long expensive learning curve.
Anyway lets try to focus on getting it right now and running corectly please, otherwise the fortune ive spent is dead money.
Thanks

[zed9]

Did you replace camchain on last rebuild as if not would be good time to do it now.

[Gray17]

Thanks zed9 for suggestion, no camchain wasnt replaced last time but was thoroughly tested with no appreciable wear and its a DID so may have been replaced in its past. When i split cases for vapour blasting, maybe should have done it then, but reasons i didnt were down to: 1. there supposed to last between 80k and 100k at 20k mine only 20-25% through its life, 2. its not stretched and no play in links, nor does it bend much if you hold it on its end. 3. Cost at the time having to spend a fortune on parts to restore it. I did consider it but reasoned ive only done 300 miles since last strip down and the fact im not stripping the cases down to fit an endless one like original.
I know you can get open ones, but this needs to be peened over after reading several posts on this, im not convinced id do it right, using 2 hammer method. Which may either then weaken it or allow it to come loose. I cant take it in anywhere as engine in frame and its immobile at present. My worry is my attempt is more likely to fail then the original is to break!.
What i may do is take it in to get it done in the future once its running as believe it can be replaced by just removing cam cover and tensioner and top sprocket, split old chain, then attach new and pull it through.
Thanks

[Gray17]

Update, so rebore completed by IMD, new pistons supplied complete with gapped rings, pins and circlips, arrived by courier in perfect condition. Great people to deal with.
Fitted new Piston rings to pistons indoors sat down rather then garage all fitted perfect and staggered the ring gaps, next into garage and fitted inner 2 pistons 1st followed by outer 2, if youre doing this yourself as i am, its easier to fit inners 1st as the outers would get in the way. Also make sure you cover up all openings when fitting circlips as the can spring out unexpectedly. I was lucky and all went well. Then cleaned barrells with petrol to ensure no fillings then blew off with air. Next fit barrells, for this i used 2 bits of wood under the centre 2 pistons at full height. This held them upright and firm, next used a clamp on the outer stud to support barrell weight lowered just above top 2 inner piston ring, then 1 at a time alternating lowered barrells until all 3 rings were inserted, then did same with outers.
And yes i did remember the base gasket and 4 rubber o rings 1st.
So thats as far as ive got as decided to replace all 3 cam sprockets.
You may recall on my original post i made some sleeves as the rubber had disintegrated, a common occurence, whilst my idea did work it was noisy, so bit the bullet again and ordered new ones.
Once they arrive thats my next step to fit them and re fit the head.
I have whilst off cleaned the head although very little carbon. Re fitted the carb inlets with liquid silver gasket to ensure airtight seal and also replaced the 4 take off rubbers again to ensure no air leaks. I also temp re fitted plugs and poured petrol into upturned chambers then left each for an hour to check for seepage, none at all so least all valves sealing well. Another box ticked.
Will keep you all posted.

[gray]

We're all ears! keep up the good work and regular reports

[Gray17]

Thanks for the encouragement its def needed!
Update, cylinder headcre fitted and correctly torqued down, all new cam guide sprockets fitted, cam shafts installed loosely this time marked exhaust cam arrow with white paint so i know exactly where it is. Installed bearing caps and checked valve clearences.
Next the pesky cam.timing. determined to get it correct so 1 and 4 at TDC mark lined up on advance unit. Next lined ex cam up with mark on cylinder head problem is if i stretch chain tight it either 1/2 a link above or half a link below, if i set cam spot on then TDC mark doesnt line up. So which is best slightly below or above head. Not doing inlet until i know ex is correct. Thoughts please
Thanks guys

[zed1015]

Set it on the pin that is slightly below the gasket surface.