Gsxr 400 gk76a engine rattle!!

[andy_g2k7]

hi all been on this site the last few days and it is full of useful information so thank everyone for that couldn't of got as far as I have without it!

right problem in hand, bought a Suzuki gsxr400 gk76a 2 weeks ago, bit rough around the edges but for the price I couldn't moan as it had tax and test ran well pulled strong ad braked like a train. So I take it easy home and do the usual when buying a new bike for the collection (plugs, air filter, oil + filter) and parked it up ready for work the next day. it ran strong for a few days only problem being a dodgey idle but with the weekend rolling around I knew a carb clean and sink was on the cards......... or so I thought. after a short but rather fast ride (around 2 hours) I took to the motorway home for the last 2 miles. due to the noisy can on the motorway I couldn't say exactly when my problem started but it was definatly within them 2 miles. when pulling off I had a rather unusual rattle from the top end. naturally the bike got turned off and pushed home to save any further damage. parked up with cover over I went to bed rather gutted id broke my new favourite toy.

work done so far: not a lot to be honest, took rocker cover off hoping to find something easy like a broken valve spring or slack cam chain but nothing so out came the feeler gauges. my problem is nearly every shim is out by between 0.01mm and 0.08mm going of the specs I found here. could this be my problem? also the cam chain is slightly slack, around 5-10mm of slack is this correct?

ive rebuilt many single fours like my wr 400 which blew out second gear with a selector fork but since college I haven't had to touch an inline four so am a bit rusty.

Please help as I love this bike and if I can sort it im treating it to a full respray ready to come meet the other 400cc troops!

[Variablevalves suck]

You should find the cam chain is quite tight, say 5mm max.
Take a good look at the cam chain tensioner as they give up.
I also had a cam sprocket come loose and had a similar noise.

[andy_g2k7]

had the cam chain tensioner out and gave it a wiggle and it freed up and now cam chain is tight (new tensioner will be ordered if engine runs again) but now after doing the clearances it runs but only at 2k revs and to top it off it backfires out the exhaust regularly, I checked and re checked my clearances aand they are now well within specs so I think the problem is timing so any info on this would be great. I red 20 pins so that's what I set it to, when I stripped it it set piston 4 to top dead which left both the lobes on piston 4 facing out and timing mark on exhaust was set perfect and intake was about 1mm low. did clearances changed shims re did everything as it was but now backfiring! also I undo my timing plug and ther is no timing marks ther is this correct.

please help I adore this bike and want to keep it going for years to come

[andy_g2k7]

ok an update, yes I am a retard!! had plug cars on the wrong way on cylinder 3 and 4 bike fires up perfect after them clearances so thank you to this site for its sticky's on that! but my rattle is still ther. doing the official screw driver on the engine trick I have narrowed it down to the exhaust cam but ther was nothing to indicate a problem when I had it out, am I missing something stupid? the rattle is coming form exhaust cam on cylinder 4 (that location) but no rattle on the exhaust cam on cylinder 1???

[rich21]

hi I have a similar prob with mine
have owned it for about a month and on a lesurely ride home well under any speed limits
I could here a rattle but had an exhaust blow any way so thought was to do with that so pulled the exhausts off and resealed all good
but rattle is still there also sounds like its coming from right side exhaust port (maybe)
was thinking cam chain loose but not sure


any ideas