I need a good telling off for this and some advice on how to fix. Rebuilding top end

**Hamish Carlson** · 19th August 2009, 12:33

Well, my GSX400L (one of them new 1984 beasts hahahaha) went thud thud thus on my way home from timaru a week or so again, running on one cylinder from temuka to Clandeboye

. I know, my bad for something this bad happening and not stopping, - oil light came on as I got to my drive. Left it for a day or so, went to start it the next night and she fired into life, with an excruciating tappet noise, and no power. No oil light, which was good. ANYWAY, time for a rebuild anyway - I haven't done one on a four stroke before, nor DOHC or 2 cylinder engine, not that that stopped me thinking I could give it a whack

. So off came everything to get the motor out - figure this would make life easier and if all goes well I needed to get the airbox out to put pods on carbs anyway. Motor came out tickeyboo, time for the rocker cover... came off fine, took some photo's so I could remember where and how it all went. Had a look at shims - all evenly spaced, albeit wrong spacings - not what was making the noise though I thought. So off came the head, ready to take to mechanics to get valve springs out so I can grind them (very dirty with 60000km of crap), but alas, on taking off head, some dust and grit fell down onto a piston... and down cam chain hole. My question - should I be very worried about this killing something low end? I put the vacuum down the hole and got most of it, just some dust in there now, but somewhat worried. If anyones taken a GSX400 twin engine apart from the 1980's any tricks to help would be helpful. And I know your all going to say take it to the bike shop, but a quote for 8 hours work and $70ph kind of put me off that, as its a $1000 bike and only reason shes still going is shes my baby.

**birdhandler** · 19th August 2009, 15:01

you may be better buying another motor off trademe mine cost $115 on trade me about six months ago . its in good nick too, otherwise you are looking at spending $1000.00 + rebuilding the engine. fine if its going to e a project otherwise buy another $1000.00 bike how long did this one last.
The engines are widely regarded as bulletproof a reputation you are trying to change 30 years down the track!!
there is a manual on thenet as well
Cheers goodluck

**Hamish Carlson** · 19th August 2009, 19:31

On kb I saw a link for the manual, but it was old and not running anymore. I already have the rings and gaskets, and I have plenty of time on days off to tinker. To be fair - 30ishkm/L, and 60,000km without anything done to the engine I regard for a bike pretty great

, but she has hard out glazed barrels and the tappet noise as a result. If I rebuild the engine, I can learn, and enjoy my passtime.

**Crisis management** · 20th August 2009, 15:44

Ummmm, if the motor lost one cylinder, made a "new" loud noise and the oil light came on I wouldn't immediately think the tappets needed adjusting, more like the crank bearings or something of that ilk. Grinding the valves and adjusting the tappets probably isn't going to fix that.

You may want to investigate further ie; strip & inspect the entire motor, before you spend time and money on the head. Once you know the extent of the problem then decide what is your most economical choice of action.

**CookMySock** · 20th August 2009, 15:50

Originally Posted by Hamish Carlson

some dust and grit fell down onto a piston... and down cam chain hole.

I wouldn't worry about it unless it was a good handful of sand. The strainer and the filter will pick that up in the first two minutes of running time.

Check the longitudinal play in the con-rods when you have the bores off. I bet they are a little loose, and if so, the motor has to be split.

I understand its about $160 to get the crank split, new big-end bearings fitted, and pressed back together again, though you should get your own quote for that.

Steve

**Hamish Carlson** · 21st August 2009, 08:42

Dangerousbastard and crisis. Will work my way down.

**Taz** · 21st August 2009, 09:00

Good luck. Oh and keep the airbox. It'll run like shit with the pods.

**Hamish Carlson** · 21st August 2009, 12:37

the problem with the airbox is it doesn't seal around the carbs as the flange on the box is poked. It should run better with pods and a calibration

**Taz** · 21st August 2009, 13:31

Ok .

**birdhandler** · 21st August 2009, 17:19

worth a look only $20.00
http://www.trademe.co.nz/Trade-Me-Mo...-237285241.htm

good luck
cheers

**Hamish Carlson** · 21st August 2009, 18:04

You were spot on as to the problem, and crisis you were damn right too. Managed to get cylinders off today after work, and low and behold, one piston felt fine and looked like it should, the other however has about 1mm of play up and down. Anyone know anyone in Timaru/chch that would do the crank splitting deal and replace the big end bearings?

**Henk** · 21st August 2009, 18:49

Gete new / better rubber bits to join the carbs to the airbox and head. If you go down the pods road you will have to spend time jetting to suit and you'll be balancing the carbs every three weeks. Bought a bike with pods once, won't make that mistake again.

**CookMySock** · 22nd August 2009, 07:56

If it were me, I'd just take the whole bottom end to the bike shop, point at the shonky rod, and ask them to sort it. They'll split the cases, pull the crank out and send it away for you. You get the advantage of someone experienced to check the important bottom end over for you. But hey, if you feel confident, then do it.

Steve

**Ixion** · 22nd August 2009, 08:54

Is the GSX400 a built up crankshaft? I thought they were a four cylinder, a 4 cylinder pressed up crank would be rare.

**Hamish Carlson** · 22nd August 2009, 09:24

parallel twin. I do not in the least bit feel confident playing around downstairs of an engine just yet. I'll take it into the shop on monday, when I get the barrels honed and valve springs taken out