Engine Gurus

benny13 · #1 13th March 2012, 08:43 AM

Question for the engine gurus!
I have a complete spare(in pieces) XTZ750 engine and a complete TRX850 topend including barrels & pistons.

My question is if I was to put the barrels & pistons from the TRX onto the XTZ bottom end and use the cams from the XTZ, basically all I'll be doing is increasing the bore with the same stroke.

1- I must check to see if the depth of the pistons are the same.
2- If pistons on the TRX are shorter I'll be increasing the bore but decreasing the stroke.
3- If the pistons are longer I'll be increasing the bore and increasing the stroke too, which I will have to use the TRX head, but still use the XTZ cams.

hope I'm making sence or am I only dreaming and this would be a complete waste of time, just a side project is all it would be, but if all fitted nicely I would consider putting it into the tenere
To view pics on this biker's forum - your post count must be 2 or greater.

cheers lads
To view pics on this biker's forum - your post count must be 2 or greater.

jimgoose · #2 13th March 2012, 08:45 AM

Stroke is dictated by the crankshaft throw. A shorter piston crown would affect compression, not really the stroke. What's the craic with the con-rods?

slapper · #3 13th March 2012, 08:48 AM

the answer to all your questions is yes
To view pics on this biker's forum - your post count must be 2 or greater.

benny13 · #4 13th March 2012, 09:09 AM

Originally Posted by jimgoose

Stroke is dictated by the crankshaft throw. A shorter piston crown would affect compression, not really the stroke. What's the craic with the con-rods?

the con rods are from the XTZs big end, since the TRX barrels and head is a direct mount, the centers will suit the TRX barrels & pistons.

I will check to see it the barrels length is the same between both
To view pics on this biker's forum - your post count must be 2 or greater.

but if the rods are different lengths,i.e barrels are different lengths, I have a problem there ya?
I will loose compression, and this would be a waste of time?
To view pics on this biker's forum - your post count must be 2 or greater.

Originally Posted by slapper

the answer to all your questions is yes
To view pics on this biker's forum - your post count must be 2 or greater.

I know the answers yes, just want to know is it worth it
To view pics on this biker's forum - your post count must be 2 or greater.

jimgoose · #5 13th March 2012, 09:19 AM

Originally Posted by benny13

the con rods are from the XTZs big end, since the TRX barrels and head is a direct mount, the centers will suit the TRX barrels & pistons.

I will check to see it the barrels length is the same between both
To view pics on this biker's forum - your post count must be 2 or greater.

but if the rods are different lengths,i.e barrels are different lengths, I have a problem there ya?
I will loose compression, and this would be a waste of time?
To view pics on this biker's forum - your post count must be 2 or greater.

I should think so, yes. Compare the lengths from the geometric centre of the big-end to the top of the piston crown. I'd say you can safely ignore any funny contouring on the top of the piston for the moment - the heads will most likely have subtly different squish.

benny13 · #6 13th March 2012, 09:20 AM

Originally Posted by jimgoose

I should think so, yes. Compare the lengths from the geometric centre of the big-end to the top of the piston crown. I'd say you can safely ignore any funny contouring on the top of the piston for the moment - the heads will most likely have subtly different squish.

cheers goose
To view pics on this biker's forum - your post count must be 2 or greater.

jimgoose · #7 13th March 2012, 10:00 AM

Originally Posted by benny13

cheers goose
To view pics on this biker's forum - your post count must be 2 or greater.

Oh, one more thing as you're at it - weigh the pistons. If the TRX crowns are heavier and/or the new arrangement allows the XTZ crank/rods to spin more RPM, then you're looking at more inertia at TDC/BDC which could cause trouble.
To view pics on this biker's forum - your post count must be 2 or greater.

**chopper** · #8 13th March 2012, 12:34 PM

Theres something on the 750 thats not on the 850 .ill remember it later but iirc this mods been done a few times before so its a runner.

HIGHSIDER · #9 13th March 2012, 01:01 PM

Originally Posted by jimgoose

Oh, one more thing as you're at it - weigh the pistons. If the TRX crowns are heavier and/or the new arrangement allows the XTZ crank/rods to spin more RPM, then you're looking at more inertia at TDC/BDC which could cause trouble.
To view pics on this biker's forum - your post count must be 2 or greater.

What about the crank itself? Could this adjustment cause an unbalance?

**chopper** · #10 13th March 2012, 01:14 PM

Originally Posted by jimgoose

Oh, one more thing as you're at it - weigh the pistons. If the TRX crowns are heavier and/or the new arrangement allows the XTZ crank/rods to spin more RPM, then you're looking at more inertia at TDC/BDC which could cause trouble.
To view pics on this biker's forum - your post count must be 2 or greater.

Meh ..that theory would be same for all bigbores then

**chopper** · #11 13th March 2012, 01:16 PM

Originally Posted by HIGHSIDER

What about the crank itself? Could this adjustment cause an unbalance?

The cranks are different degrees but are swapable throught the range iirc

LittleBlackBlade · #12 13th March 2012, 01:34 PM

Ive heard of lads doing it before so it should work fine!

but why anybody would want to put more stress on the softest gearbox known to man is beyond me!

HIGHSIDER · #13 13th March 2012, 01:35 PM

Originally Posted by chopper

The cranks are different degrees but are swapable throught the range iirc

To view pics on this biker's forum - your post count must be 2 or greater.

benny13 · #14 13th March 2012, 01:42 PM

cheers chopper, I'll take the 2 out later this evening and will temporarily marry them together and see what it looks like
To view pics on this biker's forum - your post count must be 2 or greater.

jimgoose · #15 13th March 2012, 01:50 PM

Originally Posted by chopper

Meh ..that theory would be same for all bigbores then

Mmm. Don't a lot of big-bore kits/race kits feature stronger conrods though?

Originally Posted by HIGHSIDER

What about the crank itself? Could this adjustment cause an unbalance?

Wouldn't think so, not an unbalance. Could trollix up valve timing...

Originally Posted by chopper

The cranks are different degrees but are swapable throught the range iirc

...unless you did that.
To view pics on this biker's forum - your post count must be 2 or greater.

Harrington · #16 13th March 2012, 03:18 PM

Originally Posted by jimgoose

Mmm. Don't a lot of big-bore kits/race kits feature stronger conrods though?

Wouldn't think so, not an unbalance. Could trollix up valve timing...

...unless you did that.
To view pics on this biker's forum - your post count must be 2 or greater.

Most don't.The theory behind inertia might mean something with a race bike living on the redline but this is pretty far removed from being a racer.There's plenty of aftermarket big bore kits that have heavier then standard pistons but run higher compression domed tops and run well.Theory is one thing and reading is all well and good but actual time spent tooling engines together is what counts for experience and knowledge.

slapper · #17 13th March 2012, 05:07 PM

Originally Posted by benny13

I know the answers yes, just want to know is it worth it
To view pics on this biker's forum - your post count must be 2 or greater.

i was just taking the piss
so it does work
To view pics on this biker's forum - your post count must be 2 or greater.

To view pics on this biker's forum - your post count must be 2 or greater.

To view pics on this biker's forum - your post count must be 2 or greater.

To view pics on this biker's forum - your post count must be 2 or greater.

jimgoose · #18 13th March 2012, 06:42 PM

Originally Posted by Harrington

Most don't.The theory behind inertia might mean something with a race bike living on the redline but this is pretty far removed from being a racer.There's plenty of aftermarket big bore kits that have heavier then standard pistons but run higher compression domed tops and run well.Theory is one thing and reading is all well and good but actual time spent tooling engines together is what counts for experience and knowledge.

Right so Ted. I'll just fuck off and die then, if you don't mind?
To view pics on this biker's forum - your post count must be 2 or greater.

Harrington · #19 14th March 2012, 12:21 AM

Originally Posted by jimgoose

Right so Ted. I'll just fuck off and die then, if you don't mind?
To view pics on this biker's forum - your post count must be 2 or greater.

Taking it the wrong way there Jim.There's no point giving the guy secondhand info from a textbook here,just give him a lend of the book if that's the case.He's building a hybrid motor,Ive done a few myself and the last thing you need to be doing is complicating the matter by worrying about stuff that you don't need to worry about. Admittedly you have a good grasp on the ongoings of an engine but to me it just doesn't come across as being from a practical point of view and that can be very off putting for someone taking your advice if they are none the wiser.

jimgoose · #20 14th March 2012, 09:24 AM

Originally Posted by Harrington

Taking it the wrong way there Jim.There's no point giving the guy secondhand info from a textbook here,just give him a lend of the book if that's the case.He's building a hybrid motor,Ive done a few myself and the last thing you need to be doing is complicating the matter by worrying about stuff that you don't need to worry about. Admittedly you have a good grasp on the ongoings of an engine but to me it just doesn't come across as being from a practical point of view and that can be very off putting for someone taking your advice if they are none the wiser.

You make a fair point of course - I haven't built many hybrid engines, but I am an engineer, and I know what makes stuff blow up! Also, I know who I'm talking to - Benny knows one end of a crankshaft from the other. All I'm saying is if I had the guts of both motors in front of me on a bench, and was planning grafting piston crowns from one onto conrods from t'other, I'd take two minutes to pop the crowns on a kitchen scales. As an insufferable nerd I'd want to know, and would consider it worth pondering the results for ten minutes over a mug of tae and a fag. YMMV.
To view pics on this biker's forum - your post count must be 2 or greater.

Live long, prosper, and may your engines never operate in Claymore Mine mode.
To view pics on this biker's forum - your post count must be 2 or greater.

To view pics on this biker's forum - your post count must be 2 or greater.

To view pics on this biker's forum - your post count must be 2 or greater.