Too much compression?

[Just a bill]

Hey guys I'm having trouble with the start shaft stripping I changed to the roto start from the pull start because it was just to hard to pull I think it has too much compression with no fuel in it once the glo plug is in I was able to pull the rope with my foot on the truck any time the motor turns over it fires up and really runs great so much power even with the wheelie bar it will flip itself over any time I nail the throttle and that's in loose dirt any advice on how to lower the comp.? Thanks

 

[Jam 1]

Let it wear in, for easier starting loosen the plug a turn or two and tighten after it is running..... as for the flipping over backwards, try loosening the slipper a half turn or so and see if that helps

 

[Just a bill]

It's not a new truck I've had it for couple years always been very hard to pull start broken many pull starters (7) it has 2 round copper washers under the head can more be used to lower comp?I do keep the slipper loose if not instant stripped spur gear had to go to metal spur to stop that even while rolling part throttle in loose dirt it will flip so hard I can flip it back on it's wheels do all savages do that?

 

[Jam 1]

It's not a new truck I've had it for couple years always been very hard to pull start broken many pull starters (7) it has 2 round copper washers under the head can more be used to lower comp?I do keep the slipper loose if not instant stripped spur gear had to go to metal spur to stop that even while rolling part throttle in loose dirt it will flip so hard I can flip it back on it's wheels do all savages do that?

Put your foot on it ???? try short tugs on the pullstart, most times it will work fine, if you pull out the string all the way it is sure to come apart, second question is yes they are all front light so wheelies and flip overs are common, try being easier on the throttle starting out, let the rig take a set then once you have a bit of speed you can get after it a bit more. My Savage X with a .32 will virtually backflip if it has enough traction from a start..... the truck is high up and front light you will need to finesse the throttle a bit...

 

[Just a bill]

Put your foot on it ???? try short tugs on the pullstart, most times it will work fine, if you pull out the string all the way it is sure to come apart, second question is yes they are all front light so wheelies and flip overs are common, try being easier on the throttle starting out, let the rig take a set then once you have a bit of speed you can get after it a bit more. My Savage X with a .32 will virtually backflip if it has enough traction from a start..... the truck is high up and front light you will need to finesse the throttle a bit...

Well like I said even when it rolling at part throttle on loose dirt it will still flip I have a 7.4v LiPo batt zip ties inside the front bumper to power the servo's and it will still flip with that added weight you can't pull the rope with one hand and hold the truck with the other hand it won't turn over what I'm asking about is the round copper washers under the head can more than two be used to lower the compression I can tell the compression is really high because if you hold a lot of pressure in the pull start rope you can feel the pressure bleed off and then the motor will turn until the piston comes back up then again it's to hard to pull without putting your foot on it I'm not pulling the rope out far only about 7-8 in.does anyone know if stacking more copper washers will lower the compression? I got this truck used just over 2yrs ago maybe prev.owner did some mid that raised the comp.anyone know of a mod I can look for that does that? Thanks folks just trying to start it easier

 

[guinnessdublin]

Have you pulled apart the clutch & inspected the shoes/springs, I would be tempted to install new clutch shoes & springs?

 

[lokky]

To ease starting, preheat the engine and/or loosen glow plug a fraction but retighten before drivng. The engine is? Have you have to replace the one way bearing?

 

[Just a bill]

Have you pulled apart the clutch & inspected the shoes/springs, I would be tempted to install new clutch shoes & springs?

The clutch is fine I'm asking about the copper washers under the head nobody has said a word about that so I'll find out for myself today I have brass shim material from .003to .020 thick and the punch dies to make what ever I need.i assume the high comp.is needed to help fire the nitro fuel I just got the things needed to build a small compression tester so I'll take a before and after reading then I'll post it it's not a clutch issue,or too much fuel in the cyl.i don't pull the rope too far out you can't hold the truck and pull the rope one handed it has too much compression I'll post my results to clear it up for everyone

 

[Gazzman]

1st off what engine you talking about, different mills have different amounts of head shims on them.

 

[guinnessdublin]

Well if your happy with clutch set up before playing around with head shims I would loosen g/plug slightly when starting as lokky has suggested first, the shims are there for a reason & not to be played around with in my opinion!

 

[Just a bill]

To ease starting, preheat the engine and/or loosen glow plug a fraction but retighten before drivng. The engine is? Have you have to replace the one way bearing?

I removed that bearing don't use them every one I tried never turned the motor over once.i filed a small flat on the crank and put a hex bushing with dual set screws on it it has never slipped.i have a special socket I made and a shaft with a swivel I also made that works great it never binds or slips I tried the roto start just twisted the shaft into .again what I was asking about are the round copper washers that I think are head gaskets if using more than two would lower the compression I'll find out for myself tonight and let all of you know .I guess nobody has ever bothered to get a true compression number on these nitro motos?thanks folks I'll handle it from here I'll let you know the results

 

[Just a bill]

1st off what engine you talking about, different mills have different amounts of head shims on them.

I think it is a 4.6 will adding or taking away those shims affect the compression? if they do then that's my trouble.need more shim to raise head away from piston

 

[Gazzman]

Well if you let peps know what mill you are running then you might get some help on the head shims. There's alot of folks on here with alot of knowledge, but you need to give us a clue as to what mill you need answers to.

 

[Gazzman]

Ok, so it's a 4.6 but what make. like i said all have different amount of head shims. Upload some photos of it to help us help you.

 

[Gazzman]

I think it is a 4.6 will adding or taking away those shims affect the compression? if they do then that's my trouble.need more shim to raise head away from piston

Anyway in answer to the question about adding head shims. If you add shims yes it will lower the compression on any mill as will increase the combustion chamber size.

 

[Gazzman]

Ok so here's what I know about head shim specs going by what mills I have
Nitro Star 25 =3 shims
Force F3.5 or HPI 3.5 = 3 shims
HPI F4.6 = 4 shims
King Star 4.6 or HPI K4.6HO(HPI Pulse 4.6 mill) =2 shims
Force F5.2 = 2 shims
Force F5.9 or HPI F5.9 = 2 shims
Force F4.6 = 2 shims
King Star 5.8 or HPI K5.9 = 2 shims

Now all these numbers are taken from the original engine manuals. Now don't ask me why the Force F4.6 has 2 shims and the HPi F4.6 has 4 as they are the same mill as Force makes the HPI F series engines.
Hope this helps.

 

[Jam 1]

I think it is a 4.6 will adding or taking away those shims affect the compression? if they do then that's my trouble.need more shim to raise head away from piston

simple answer is YES those shims will raise or lower the compression depending on how many, one thing to keep in mind is these 2 stroke nitro engines do need a certain compression to burn the mixture, you can stack shims to lower it a bit if that is the question, but tuning a low compression engine can be a bit of a troublesome thing....

I still say to loosen the glow plug for starting then tighten it back up to run the truck, but you seem to be stuck on a problem that is not really a problem....Maybe a strip down of said engine to check it out is in order...

 

[Gazzman]

simple answer is YES those shims will raise or lower the compression depending on how many, one thing to keep in mind is these 2 stroke nitro engines do need a certain compression to burn the mixture, you can stack shims to lower it a bit if that is the question, but tuning a low compression engine can be a bit of a troublesome thing....

I still say to loosen the glow plug for starting then tighten it back up to run the truck, but you seem to be stuck on a problem that is not really a problem....Maybe a strip down of said engine to check it out is in order

@Jam 1 , Very well said mate.

 

[Just a bill]

Ok, so it's a 4.6 but what make. like i said all have different amount of head shims. Upload some photos of it to help us help you.

Sorry for not being clear on the make I thought this was a hpi savage forum thinking that was the rig discussed here I have what I think is an hpi savage and what I think is the 4.6 motor that came in it.i bought used 2years ago for 20$ got it running amazed at how it blows my tMaxx 3.3 away except for the hard to turn over truck Is great someone post on the head shims the hpi 4.6 should have 4 shims instead of 2 I now have that would increase comp bit I'll add 2 more I don't mean to piss anyone off I'm 60 yrs old trying to play with my trucks sometimes I need to ask questions without knowing just how to ask them again I'm sorry folks

 

[Jam 1]

Sorry for not being clear on the make I thought this was a hpi savage forum thinking that was the rig discussed here I have what I think is an hpi savage and what I think is the 4.6 motor that came in it.i bought used 2years ago for 20$ got it running amazed at how it blows my tMaxx 3.3 away except for the hard to turn over truck Is great someone post on the head shims the hpi 4.6 should have 4 shims instead of 2 I now have that would increase comp bit I'll add 2 more I don't mean to piss anyone off I'm 60 yrs old trying to play with my trucks sometimes I need to ask questions without knowing just how to ask them again I'm sorry folks

Bill I don't think anyone is/was pissed off, just that there are several stock engines that were used by HPI over the years, everyone is here to get info and share the same, I am also an OLD SOB but I have nearly 40 years in the hobby... I am also retired and still playing with toy trucks, ask away on most subjects there will be someone with info and willing to help....

 

[Gazzman]

Sorry for not being clear on the make I thought this was a hpi savage forum thinking that was the rig discussed here I have what I think is an hpi savage and what I think is the 4.6 motor that came in it.i bought used 2years ago for 20$ got it running amazed at how it blows my tMaxx 3.3 away except for the hard to turn over truck Is great someone post on the head shims the hpi 4.6 should have 4 shims instead of 2 I now have that would increase comp bit I'll add 2 more I don't mean to piss anyone off I'm 60 yrs old trying to play with my trucks sometimes I need to ask questions without knowing just how to ask them again I'm sorry folks

Hi @Just a bill, your not pissing anyone off bud, I to am almost 60, age is just a number. Your as old as you well in my eyes.
Yer right this is a forum for savages but many of us run different mills in our trucks & not just the HPI ones.
firstly if you got it for $20, nice one that was a steal. and 2nd the HPI 4.6 & the Force 4.6 are the same mill as Force make the HPI F4.6. Force use 4 shims on there branded engines were as the HPI F version only use 2, don't ask me why.
As for asking question well that what the forum is all about.

 

[Just a bill]

simple answer is YES those shims will raise or lower the compression depending on how many, one thing to keep in mind is these 2 stroke nitro engines do need a certain compression to burn the mixture, you can stack shims to lower it a bit if that is the question, but tuning a low compression engine can be a bit of a troublesome thing....

I still say to loosen the glow plug for starting then tighten it back up to run the truck, but you seem to be stuck on a problem that is not really a problem....Maybe a strip down of said engine to check it out is in order...

As it turns out those shims are the problem there was only 2 shims and there should be 4 every thing about the truck is great except for the hard to turn over part I'm replacing the missing 2 shims as I post this I'll know for sure in less than an hour the shims are the problem I did try loosening the glo plugs but couldn't keep the motor running long enough to tighten it

 

[Just a bill]

Bill I don't think anyone is/was pissed off, just that there are several stock engines that were used by HPI over the years, everyone is here to get info and share the same, I am also an OLD SOB but I have nearly 40 years in the hobby... I am also retired and still playing with toy trucks, ask away on most subjects there will be someone with info and willing to help....

Thanks for that I have been a mechanic / high performance specialist my whole life working on ,building,and racing Harleys I was sure about the head shims just wanted anyone to confirm what I thought that's why I was fixed on the shims I'll know if I was right in about 15 more minutes I'll post what I find out

 

[Just a bill]

Hi @Just a bill, your not pissing anyone off bud, I to am almost 60, age is just a number. Your as old as you well in my eyes.
Yer right this is a forum for savages but many of us run different mills in our trucks & not just the HPI ones.
firstly if you got it for $20, nice one that was a steal. and 2nd the HPI 4.6 & the Force 4.6 are the same mill as Force make the HPI F4.6. Force use 4 shims on there branded engines were as the HPI F version only use 2, don't ask me why.
As for asking question well that what the forum is all about.

I didn't know you could change motors and haven't heard of force before I have no experience with any other rc's except my tMaxx I added 2more shims and I can now use the roto start for the first time the motor starts easily it seems to have lost a small amount of performance which I'm fine with it keeps the front wheels down and pulling like it should I'm calling this issue fixed thanks to all that responded to help I was able to get the info I needed to solve my troubles thank you all

 

[Just a bill]

Ok, so it's a 4.6 but what make. like i said all have different amount of head shims. Upload some photos of it to help us help you.

I didn't know there was another 4.6 all I've ever heard about was the hpi 4.6and 5.9 and the traxs.3.3 that's why I'm on the forum trying to learn something thankfully I found out what I needed to know despite not giving the right info or asking the question in a way to make it clear I'll do better folks next time thanks to everyone for their input

 

[Gazzman]

I didn't know there was another 4.6 all I've ever heard about was the hpi 4.6and 5.9 and the traxs.3.3 that's why I'm on the forum trying to learn something thankfully I found out what I needed to know despite not giving the right info or asking the question in a way to make it clear I'll do better folks next time thanks to everyone for their input

Glad your all sorted now, and just for some information for you there were 2 4.6 mills available in the savage trucks the early ones were fitted with a K4.6 with the later having the F4.6. below are what they look like so you can see which one your savage is running. another way to tell the difference is by the carb with the K4.6 having a 3 needle carb & the F4.6 having only 2.

This one is a K4.6



This one is the F4.6