spacer plate motor

[hartwill]

hey guys I'm getting ready to put my motor back together. its a long rod crank with an 86 jug and piston. I recalled after I put it together last time reading somewhere that with that combination you really want a 3.5mm spacer not a 5mm(which I have) is there any truth to this? also I run a cr head gasket and I remember it saying something about doubling up base gasket or something. oh and the motor ran really strong with the 5mm plate but if its not what I need is like to correct it while its apart. thanks

[hartwill]

Found it. Here's the link does this make sence to you guys?http://www.trx250r.net/trx250rforums/index.php?showtopic=3894

That’s Neil’s post, and as always; Neil gives great advice…

Carlos.

[hartwill]

I'm not doubting him but the numbers just don't add up to me. And ESR said that combination will not work.

A previous Pro-X cylinder I had, I used a 4.7MM (.1875") spacer plate and two .5MM (.020") gaskets.

This particular set up had the cylinder decked top & bottom, piston edge was .005" from the top of the cylinder.

Carlos.

[hartwill]

ok but I still don't understand why. if you add 5mm to the length of your rod and then raise the cylinder 5mm you should be back to even. unless he is saying the piston didn't sit flush with the top of the cylinder from the factory? thanks for helping me with this, I'm sure once I get it ill feel like a dummy.

[mxduner]

take into consideration the piston pin location on the 86 piston vs. the 87-89 piston. 86 pin sits lower by 5mm if i am correct.

[hartwill]

RIGHT THATS WHAT IM GETTING AT. THE ONLY THING THAT CHANGES IS THE CONNECTING ROD (5MM LONGER) SO YOU ADD A 5MM SPACER. OH WELL I GUESS ILL JUST FIND OUT WHEN I PUT IT TOGETHER.

[C-LEIGH RACING]

:ermm: :p Well, I see its going to take a little while for ya'll to understand.
No problem though, it did me as well a long time ago.

Ok, you talked to ESR, right, but at the new ESR shop, Eddies probably the only one there from the old shop & probably the only one ever worked on a 250R with a stock cylinder, so how would any of the rest of them know.
Now they could know, but for them to say that change over wouldnt work, sounds to me like they dont.

What you guys are missing, is, the wrist pin hole in the 85/86 model TRX250R pistons not machined in the same place as it is on the 87/88/89 model TRX250R pistons.
The hole in the 85/86 has not been shifted 5mm either.
Thats the part you are missing, its not a full 5mm of distance the pin hole has been moved.

The 85/86 piston was first to be produced & then when the longer rod change came about in 87, the 87/88/89 model pistons that wrist pin hole was relocated 5mm higher up in the piston casting.

I'll need to go to the shop & measure both years & see what the difference in height measurment is, cause I dont have it in my head right now, but I'll find out what that is.
Neil

[86 Quad R]

that's what i was/am curious to know...... whether or not the wrist pin was ACTUALLY relocated the same (5mm) distance as was added to the 87- 89 rod. if i had a good 85-86 and 87-89 crank i would have already made the comparison by installing each in the same set of cases, using the same cylinder ect ect. :cool:


by the way neil... what would be the effect if one was to use the 3.5mm spacer on a pro-X 310 cylinder and a long rod crank and 85-86 style piston?

[turboTony]

You also need to take into consideration the thickness of the gaskets, as you'll need an extra. ;)

[Pumashine]

Originally posted by C-LEIGH RACING
:ermm: :p I'll need to go to the shop & measure both years & see what the difference in height measurment is, cause I dont have it in my head right now, but I'll find out what that is.
Neil

Yeah, it sure would be nice to have prints for the different year pistons to see what the difference in pin height is.

[86 Quad R]

Originally posted by Pumashine
Yeah, it sure would be nice to have prints for the different year pistons to see what the difference in pin height is.

here here!! i 2nd that. :cool:

however, my builder/machinist has a data base compiled from fellow racers/builders. :cool:

[hartwill]

ok, I just measured two very definate ring marks in two 86 cylinders.1 is the cylinder I was running with my 5mm spacer and one from a completely stock 86 motor, I measured both from the top of the cylinder to the top of the ring marks, the spacer plate cylinder read .204 and the stock motor cylinder measured .199(I did also have the calipers facing away from me so I couldn't cheat). I then measured the pistons that were in them from the edge of the top of the piston to the top of the rings. I then subtracted these numbers. so the tops of the edges of the piston to the tops of the cylinders were within .005 of eachother. now I do see what c-leigh is saying there is approximately 1.18mm of space from the top of the cylinder to the edge of the piston in both cylinders. so I am assuming this is a factory clearance and not an error by who ever designed these plates. now correct me if I'm wrong but I think c-leigh is talking about using a thinner plate to increase compression and farther boost performance.

Obviously you measured and came to some definite conclusions as to the cylinders & pistons before you.

The real thickness of the spacer plate will be dictated by your build, it is very difficult to standardize what spacer plate thickness you need or how many base gaskets to use until the cylinder is assembled to the engine and the resulting timing, piston height and squish band can be measured. Not all cylinders are the same; factory Honda cylinders can vary 1MM (.040”), some may have been cut on the top, bottom or both…

The true spacer plate thickness needed & number of gaskets used will be determined by your designed build, your performance goal, and your final assembly.

Carlos.

[hartwill]

DOes any one have one if these 3.5 mm spacers for sale or a 5mm I will turn it down to 3.5mm. Also does anyone have any idea what kind of compression I should expect from this setup with a cr head gasket?

[86 Quad R]

PM sent hartwill. :cool:

[C-LEIGH RACING]

Measurments,
Only pistons I had was a cast 85/86 & forged Wiseco 87/88/89

From top of wrist pin to timming edge of crown,
Cast, 85/86 model
28.65mm 1.1325

Forged, 87/88/89 model
23.88mm 0.9375

The old 85/86 model TRX piston, is 4.77mm taller than the 87/88/89 model, but, that is between a cast & forged & there could be some difference if a cast versus cast was used.

I have 1.5, 3.0, & 7.25 plates that I could measure, so it is probably the 2.5 & 3.5mm plates that you cant find unless you have the sheet metal machined down.
Neil

[hartwill]

ok so with 2/ .02 thick base gaskets I would need a .155 thick spacer plate instead of the .190 that every one sells right? sorry to convert to standard I'm not sure how thick a base gasket is in mm. also is it still ok to do this with a cr style head gasket? and do oh know what kind of compression I can expect?

[86 Quad R]

before you do much else. i would back up a second and take into consideration as to what cylinder are you using and what porting does it have and go from there to best utilize its power, having a spacer plate made accordingly. afterwards you can consectrate on the head, gasket thickness and ect to get the desire compression. just my .02 worth. :cool:

[C-LEIGH RACING]

Originally posted by 86 Quad R
before you do much else. i would back up a second and take into consideration as to what cylinder are you using and what porting does it have and go from there to best utilize its power, having a spacer plate made accordingly. afterwards you can consectrate on the head, gasket thickness and ect to get the desire compression. just my .02 worth. :cool:

And, you got to go metric.
Nothing on these engine are american measurement & your beating yourself up trying to figure it out in american.
A standard 250R base gasket, is between 0.0190~0.0200, one half mm.
1mm is less than 0.0390.
Neil

[hartwill]

ok here is exactly what i have maybe you guys can point me in the right direction. i have an 86 motor brand new oem long rod crank, 67 mm 86 style wiseco piston, cr head gasket, 4.8 mm spacer plate, fmf sst pipe with a sparks silencer, mild porting (just flow porting not to emphasize any certain power band) and cr boysen rad valve, and 39mm pwk a/s. Before i had the exact same set up with a wiseco long rod, 4.8 mm spacer,turbinecore 2 silencer and stock reeds and a stock carb and it ran excelent. but like everyone i am just looking for that extra little bit. thank you guys so much for all your help. also i do mostly fasst trail riding and hare scramble races, so im assuming i want like a mx style power.

[C-LEIGH RACING]

If you use the 4.8 spacer, piston will be down in the bore some at TDC.

With a 3mm spacer plate & 3 base gaskets & the cylinders not been cut to death on the deck or base, that piston should be sticking out over the deck surface just a hair,,,, so, you cant use the CR head gasket, not unless you have the head squish cut to the proper clearance.

With out seeing the engine & just guessing, I would say you could probably get by with the Cometic head gasket & end up around 0.035~0.040 squish. Squish is going to be the deal though. I've run them at 0.035, but you got to stay on your toes with timming & jets.
Neil

You said: "ok here is exactly what i have maybe you guys can point me in the right direction. i have an 86 motor brand new oem long rod crank, 67 mm 86 style wiseco piston, cr head gasket, 4.8 mm spacer plate, fmf sst pipe with a sparks silencer, mild porting (just flow porting not to emphasize any certain power band) and cr boysen rad valve, and 39mm pwk a/s. Before i had the exact same set up with a wiseco long rod, 4.8 mm spacer,turbinecore 2 silencer and stock reeds and a stock carb and it ran excelent. but like everyone i am just looking for that extra little bit. thank you guys so much for all your help. also i do mostly fasst trail riding and hare scramble races, so im assuming i want like a mx style power"

If your concern is to get the most out of your engine, then again here is your answer:

The real thickness of the spacer plate will be dictated by your build, it is very difficult to standardize what spacer plate thickness you need or how many base gaskets to use until the cylinder is assembled to the engine and the resulting timing, piston height and squish band can be measured. Not all cylinders are the same; factory Honda cylinders can vary 1MM (.040”), some may have been cut on the top, bottom or both…

The true spacer plate thickness needed & number of gaskets used will be determined by your designed build, your performance goal, and your final assembly.

Carlos.

[Pumashine]

Originally posted by hartwill
but like everyone i am just looking for that extra little bit. also i do mostly fasst trail riding and hare scramble races, so im assuming i want like a mx style power.

Good luck at the races this weekend. I have to stay at work and make 250R stuff all weekend. Let us know what you ended up doing and how it all worked out!

[hartwill]

thanks, I don't know if I'm gonna make the small one this weekend, but ill definatly be at the bigger one next weekend in Indiana. me and a good buddy of mine both on 250rs. I was at the one 2 weeks ago he raced in and it was awesome hearing everyone chearing for the dinosaur, lol. sure makes all the time and money worth it.

[rsss396]

I don't see the advantage of running the thinner spacer plate for the average guy.
The 4.8 spacer with the 86 piston will only raise the cylinder a extra .020 which is equal to 1 extra base gasket.

And at the same time giving you a little more port timing.
Unlike the thinner spacer that will take away port timing.

Yes the compression will be less with the thicker spacer but any competent machine shop can mill the top of the cylinder or head .020 or more if needed to set the proper squish clearance.

The average 250r guy neither has the skill nor the tools to raise the exhaust and transfer ports back up to stock or higher port timings.

The only advantage in my mind is if a guy has a radical port timing and wants to mellow it out or if you are looking for more crankcase compression which is a whole different discussion as to the benefits of raising or lowering that.

[fearlessfred]

Originally posted by rsss396
I don't see the advantage of running the thinner spacer plate for the average guy.
The 4.8 spacer with the 86 piston will only raise the cylinder a extra .020 which is equal to 1 extra base gasket.

And at the same time giving you a little more port timing.
Unlike the thinner spacer that will take away port timing.

Yes the compression will be less with the thicker spacer but any competent machine shop can mill the top of the cylinder or head .020 or more if needed to set the proper squish clearance.

The average 250r guy neither has the skill nor the tools to raise the exhaust and transfer ports back up to stock or higher port timings.

The only advantage in my mind is if a guy has a radical port timing and wants to mellow it out or if you are looking for more crankcase compression which is a whole different discussion as to the benefits of raising or lowering that.
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