mash up engine timing

[VJ]

so I was building a gsx1100g with powerscreen cams and a gsxr DOT head,all went well, rode it to MOT and back, then it dropped an exhaust valve on the way back home.

Long story short I've done an autopsy and am about to try again with a gsxf750 head and replaced a piston but id really rather it not happen again, the way i see it, it was either a sticky valve or i fucked the timing up as all of the pistons have a mark in the exhaust valve recesses in the pistons.

Ive got the gsx11g cam sprockets on the powerscreen cams, and used the gsx11g manual to time it expecting it to respond the same but just have more lift however it didnt really pan out even though id hand cranked it and felt nothing bad during the assembly.

 

Is there anything I missed or is it possible it jumped a tooth whilst i was putting the camchain tensioner in?

 

Cheers

John

Edited April 17, 2018 by VJ

[Nik]

It could be that the arrows and numbers on the cam sprockets (which I presume you used when you installed the cams) are on different locations on the g and f cams, and you'd have to set cam timing manually. I don't know for sure, but it would explain what happened. Do you have both pairs of sprockets, so you can compare?

[VJ]

unfortunatley i dont but i seem to remember them lining up sensibly. this gsxf head thats coming has cams in it so i may consider dropping the powerscreen cams for those if i cant be certain of the timing, I dont have the kit to degree them in and even 1 tooth out will probably make a mess or at least a shite power output.

[Lachie04]

13 hours ago, VJ said:

unfortunatley i dont but i seem to remember them lining up sensibly. this gsxf head thats coming has cams in it so i may consider dropping the powerscreen cams for those if i cant be certain of the timing, I dont have the kit to degree them in and even 1 tooth out will probably make a mess or at least a shite power output.

Definitely need to degree cams, I just put a Dot head on a later motor having to change sprockets, initially with the intake remained at 104° but the exhaust went to 108° slotted the gear back to 105. Very possible yours went that way also.

GSXF head = DOT head ?? or latter??? smaller valve smaller bore one?? if it's a latter model one with the similar cam chain and sprocket would be my bet your going a bit backwards on that

[VJ]

As in it needs slotted cam sprockets no matter what? Even if i put the new gsxf DOT head and cams on? (92 teapot)

 

Can i not ignore the marks on the sprockets and just align the timing mark on the crank and the slots on the end of the cam to match the gsxg/power screen manual? 

 

I wouldnt mind degreeing it later for maximum win but ive made a bet that ill be riding it on saturday morning lol.

 

Cheers

John

[Lachie04]

50 minutes ago, VJ said:

 

Can i not ignore the marks on the sprockets and just align the timing mark on the crank and the slots on the end of the cam to match the gsxg/power screen manual? 

 

I'm not sure you could do that maybe someone with better knowledge can jump in.

The  manual only references the end notches as identifying the RH side of the cam and to correctly position the sprockets to the cam, naught about timing.

There are quite a few differences between timing marks, link lengths (number of pins) between cam sprockets (between the two different chains and motors), lift, duration, timing, point really was when changing things up like that I have found even if someone says "done this a thousand times" there is always the possibility it can go horribly wrong.

Any changes like that and I would recommend do the whole lot = degree, timing, piston to valve clearances just to be sure it's going to work.

Edited April 18, 2018 by Lachie04

[VJ]

Yeah i get your point. Im going to make a tdc finder from an old spark plug and i have a 1" dti but i dont have adjustable cam sprockets. I guess im going to have to do the best i can and see what tooth i need to level on the block.

I guess uts worth checking even if i cant degree them accurately. At least i can only be 360 degrees ÷ number of teeth on the sprocket out of time right?

Cheers

John

[VJ]

44 teeth on my sprockets meaning i could me up to 8 degrees out if i get a tooth wrong. Hmmm

[Oilyspanner]

I used the m12 engine mount bolt for a positive piston stop VJ - I had the engine out, was going to make a pos.piston stop and I then saw the engine bolt .....  just get  #1  & 4 very close to tdc and screw the bolt in against the piston. Dial gauges are cheap, or borrow one - make sure it's securely mounted, else you get all manner of readings. I normally check cam centres a bunch of times, once the same numbers keep appearing there's no chance of error. I set both exh and inlet at 105 degrees - seems to be good for std GSXR cams.

Go steady as the piston approaches the pos. piston stop, else you'll mark up the piston crown, or worse I guess ! Dialling in the cams isn't actually that difficult, just something that adds time to the job - it's essential really, especially if cams or head are different - get a better running engine too. Better luck with this one 

[VJ]

Aye im just not sure how i can do it without adjustable sprockets?  Im only ever going to be as close as 8degrees as thats what each tooth on the sprocket is equal to. 

 

Does the camchain guide in the rocker cover affect anything much?

 

Cheers

John

[Oilyspanner]

I bought adjustable sprockets on mine in a moment of feeling flush/stupid ! - would be easy to elongate the mounting holes a few mm either way with a tungsten burr. You could check the cams for safety's sake, just to see where they're at - some bikes are inaccurate as standard, most are a bit out, but not enough to worry about. The cam chain guide/ idler  needs some care when fitting, as it's easy to  move the cams. I know plenty have fitted dot heads to 1052 / 1127 / 1156 engines using just cam markings and rotor tdc position, with the different sized c. chamber there's less room for error though a tooth out probably wouldn't be good.... sounds like you could've been close with the piston/valve clearance first time round and this disappeared with some revs.

Good luck with the 750f head.

[Screwriverracing]

Hi,

wouldnt you be better of degreeing the cams in properly,and while your at it check how much lift you have on them.

youl need a degree wheel and positive stop, check on internet of how to dial them in.

Cheers SRR

[VJ]

i currently have fitted them this afternoon/evening. ended up using stock position for exhaust valve, 1 tooth retarded on inlet cam and wound the valve clearances out to 15 thou to get them to not go stiff when hand cranking with the plugs out. i'm going on the thought that as the powerscreen cams have more lift then increasing the valve clearance will retard the timing of them at a more slight degree than the 8 degrees per tooth I can do, its at the cost of some lift and duration no doubt but It just needs to be rideable for now.

 

Cheers

John

[canamant]

I'd do it right by slotting the sprockets.  Retarding the inlet by one tooth won't give valve to piston issues but it will move the crossover point to the right of TDC most probabaly and will reduce the overlap.  If you have had to open the valve clearances to 15 thou (from 6 thou?) to stop it going stiff then the valve to piston clearance is only 7 or 8 thou.  Such a set up won't last 5 minutes.

I've been doing the same with a powerscreen engine with a heavily skimmed head and trying lots of different cams.  Powerscreen cams have close running clearances at standard.  There are no quick fixes when swapping heads and cams about.  I have spent many many hours doing graph after graph on my engines to select the correct cam and timings.

 

[VJ]

Im very tempted to put the 750 cams in then and wait til i can get ape sprockets for the power screen cams then. They have .25mm less lift on inlet and .8mm less on ex so in theory they should time in better on stock sprockets,  especially being the right cams for the head?

[canamant]

Using the 750 cams shouldn't do any harm at all.  I'm not certain but I would expect the camshaft sprockets on short stroke 750s and 1127s to have the bolt holes in the same places.  Make sure you orientate the cams correctly on the sprockets.  I'm assuming you know what sprocket marks to set up to and the number of pins between the exhaust and inlet cam marks.  Set up according to the book.  If you you don't have a dial gauge (you really really should get one - they cost peanuts) you can do a very rough valve to piston check by turning the engine over a few degrees at a time from TDC and checking the inlet valve which is just starting to open (which will be on cylinder 1 or 4) push the rocker down with a lever until the valves touch the piston.  As you go past TDC the piston will get closer to the inlet valve.  When you push the valve down, try and get a feeler gauge between the cam and the rocker.  A friend might be useful at this point.  The rocker ratio is 1.5 to 1 so if you have a 40 thou gap at the cam you have a 60 thou clearance at the valve.  Closest approach should be about 10 deg ATDC but run the check from TDC to about 20 degrees after.  Inlet limit is 1mm or 40 thou at the valve or 27 thou at the cam.  if you get this clearance then take the engine to BDC and then raise it up towards TDC again.  One exhaust valve will now be almost closing with the piston approaching it.  Again have an assistant push the rocker/valve down with a lever and measure the rocker/cam clearance with a feeler gauge.  Closest approach on exhaust is 80 thou so you should be able to fit a 54 thou feeler gauge between the cam and the rocker at closest approach. 

With each of the measurements, you don't need to measure the gap, just make sure the 27 thou and 54 thou gauge will fit at every increment.

It will be easier if you print off a degree disc from the interweb and stick it to an old CD and bolt it to the ignition rotor.  You can fit a pointer from the clutch cover bolt.  Turn the engine with a slim open ended spanner on the rotor.

This method is not ideal but might give you some idea of how close the valves are getting to the pistons and whether you are heading for trouble. It is vital that you get the first inlet measurement on the first few degrees from TDC and only if that gives some clearance go to the exhaust measurement on the next BTDC.

Take it easy and slowly, feeling for any resistance.

Good luck.

Edited April 20, 2018 by canamant

[VJ]

well I put the 750 teapot cams that belong in that head back in, timed up as standard and it rolled over perfectly smoothly,  started well and runs nice. Ive got a bit of carb work to do but otherwise rideable. 

 

I'll leave the powerscreen cams in the garage until I get some adjustable sprockets and the kit to dial it in,  i'll come back to this thread for info too. Thanks to all of you for talking me out of doing stupid things again, theres a mine of information here and its mega helpful.

 

Cheers

John

[canamant]

John

As been said, slotting sprockets is easy.  Get a small round file (chainsaw file will be about right) and file the holes out.  Remember that 10 degrees at the crank is only 5 degrees at the cam.  You will find that you don't need to remove much metal, a file is cheaper than new sprockets, and you get to keep the file after you have done the job !

If you need more encouragement later on we are all here to help.

[VJ]

Cheers dude. I think im going to get another set of sprockets from somewhere that way ive got the 750 cams stillin and working. Ive only got a spare set of the thin ones and this motor has the wider type chain. 

 

For now i think ill just enjoy her over summer and then do the cams in winter. 

 

Cheers 

John

[canamant]

Wider type chain ?

[Oilyspanner]

Hy-vo type ?

[VJ]

this one is made of about 5 plates riveted together with some small gaps inbetween whereas the 750 ones (and hence my spare sprockets) look more like a small pitch final drive chain style.