Tec H50 with Oval Bore Mikuni problem ... pics and Videos ...

jaimenv

jaimenv

New Member
#81
#81
Check the cam for a extra lobe on the intake valve

Guy in this video claims better performance when doing this mod.

https://youtu.be/QEue7ph_DFY

Other than that check cam overlap on the valves.



PS The old Tecumseh H4 on my wirl wind does this also, Then the 5hp Briggs on my other mini does it but way up on rpm range. I am using china Tecumseh adjustable carburators on bnoth.
 
Sixpac440

Sixpac440

#82
#82
I took the valve to head measurement with the intake valve fully open ... I see there is a visual impression of the intake valve on the head. I wondered if the spring was weak enough for the valve to touch the head causing the "can of angry bees sound".

I will measure the valve to tappet clearance tomorrow (I work 2nd shift).

How does it look otherwise?

ole4 said:
I am not understanding valve clearance are you measuring to the head? What is the clearance between tappet and valve stem Is it correct?
Click to expand...
 
Sixpac440

Sixpac440

#83
#83
I watched the fist 2 mins of the video (I'm at work) but I will look for that ... I'm guessing this being a motorsports motor the cam is different that the stock ones ... but my Hilltoppers could benefit from that!

jaimenv said:
Guy in this video claims better performance when doing this mod.

https://youtu.be/QEue7ph_DFY

Other than that check cam overlap on the valves.



PS The old Tecumseh H4 on my wirl wind does this also, Then the 5hp Briggs on my other mini does it but way up on rpm range. I am using china Tecumseh adjustable carburators on bnoth.
Click to expand...
 
ole4

ole4

#84
#84
Good observation, I missed that it does look like the valve is coming in contact with the head. The only way is if the valves float. You measured .100 clearance at full lift. I wonder if you can lift each spring by the retainer with a screwdriver and see if it has good tension and that both springs seem to be the same.
 
Sixpac440

Sixpac440

#85
#85
ole4 said:
Good observation, I missed that it does look like the valve is coming in contact with the head. The only way is if the valves float. You measured .100 clearance at full lift. I wonder if you can lift each spring by the retainer with a screwdriver and see if it has good tension and that both springs seem to be the same.
Click to expand...
.100 seems like a lot of space to cover but if the motor has been stored for 20-some years with the intake spring compressed its possible it's sacked out.
I will contact Clements and ARC tomorrow and see if they have springs and a couple head gaskets.
I will also check the spring pressure with screwdrivers to see if anything feels fishy.
 
Sixpac440

Sixpac440

#86
#86
Just got home and was curious ..

the intake tappet to valve clearance is .011
The Exhaust clearance is .012

The valve springs "feel" the same moving them with a screwdriver.
 
danford1

danford1

#87
#87
Remove the valve springs and see if the valves wiggle in the guides. Worn valve guides can cause the valves to flutter which might be the angry bees sound and high rpm problem.
Danford1
 
jaimenv

jaimenv

New Member
#88
#88
Sixpac440 said:
Just got home and was curious ..

the intake tappet to valve clearance is .011
The Exhaust clearance is .012

The valve springs "feel" the same moving them with a screwdriver.
Click to expand...
https://youtu.be/J7ZbGgJpR-o

In the video above the guy mentions valve to tappet clearance to be between .006 and .008 to be on the good side for the engine he is working on.
If the engine is NOS the valves would have had to be cut to match the seats and lapped, chance this step was skip and makes the valves as if they where too short, actually sitting to high in the CC.
Also due to the extra clearance, this may be the source of the angry bees noise as the tappets bang on the valve stems at high rpm.

Since you are already this far in to the engine it would not hurt to tear it down completely and check everything.

Jaime

PS Found this page
Tecumseh Engine Intake and Exhaust Valve Clearances
looks like the intake is off, should be .008 and the exhaust is on the money at .012.

If you see pitting or aluminum specs on the CC this are signs of detonation (angry bees).
 
Last edited:
Sixpac440

Sixpac440

#89
#89
On the page your referencing I'm reading the exhaust and intake tolerance as .008 TO .012 ... which is correct ...


Intake and Exhaust Valve Clearance
min / max ( in. )
4-stroke L-head SOLID STATE AND EXTERNAL IGNITION VH50, TVM125, H50, HH50 .008 / .012

The tolerances are the same for the point ignition H50 ..

BUT .. this is a Motorsports motor with a non-stock cam, not a run of the mill factory cookie cutter motor.
So are those numbers correct?



jaimenv said:
PS Found this page
Tecumseh Engine Intake and Exhaust Valve Clearances
looks like the intake is off, should be .008 and the exhaust is on the money at .012.
Click to expand...
 
creia

creia

#90
#90
Kevin,
I have got to hand it to you for your work ethic and persistence- this has been a most interesting thread to follow. To really get the most out of this race engine (and more importantly get you RIDING which I know your LOVE to do) have you thought about sending the engine to Mike Clements and have HIM get it dialed in for the best/top performance? As I mentioned to you early-on in your build he is "The Man" when it comes to these Tecumseh Motorsports engine. Not only is he extremely knowledgeable, he is also a heck of a nice gentleman. Mike provided some high - performance valve springs on a H60 performance build my son did a few years ago that really woke up that engine.
Just a thought...
Michael
 
jaimenv

jaimenv

New Member
#91
#91
Looks like you will need to find another motor just like

the one you have, that is running like it should and compare specs.
What else is different other than the cam and the alloy valve spring retainers.
I ask this, because if you would replace the performance parts with stock ones, one at a time chances are you will find the culprit. I would start with the cam.

Also if all the parts are good and in spec, then like any modified engine it will call for fine tuning.

Then again this engine may be a lemon.
 
Sixpac440

Sixpac440

#92
#92
OK ... just got back from the garage ... did some measuring and calculating ...

The valves/springs were pulled and checked ... without going into detail all measurements and visuals looked good ...

The valve springs are identical in length, diameter and coil thickness.

What I do see is something I saw in the pic yesterday that I wanted to look closer at today .. there is a mark in the head where the intake valve would potentially hit ... If it's a machine mark it's the only one in this head.
Also it shouldn't be clean, it should have carbon in it like the surrounding area.


There is a definite step there that can be felt.
At 6500 RPM that valve is going 3250 RPM or opening 54.16 times a second ... I can see where a weak spring would allow to valve to open too far ... could it open .100 too much, I don't know ...
But the "Angry Bees" sound could very well be a valve hitting the head ... It comes on about 6200 and maxes out at 6500 .. makes sense anyway.

I looked at the valve and it does not appear to be bent, the seat is clean and even all the way around on the valve and block. I would expect to see a dark spot where it was bent if it was.

I will be calling Clements in a few mins to ask about springs & head gaskets.

Michael .. I don't give up easy ... and in this case as I'm going to be going to a TAV this motor will likely not see much over 5000 RPM anyway .. Problem solving is what I do for a living ... I just don't stop till I get my answers!
 
H

Havasu Dave

Moderator
#94
#94
I can not see where a weak spring allows a valve to open too far Kevin. That is a function of the keepers and gap. From what I understand, the gaps listed in the book are minimum and maximum, not intake and exhaust. Either way, your gaps are good. I agree with you on the valve hitting the head, albeit lightly. I wouldn't contribute it to limiting RPM, because if it was enough to do that, you'd have a bent valve. I would however, attribute it to the noise you hear.

I never did see if you chased fuel level at max. RPM. I have encountered that, with correctly adjusted float levels on hungry, high RPM engines. One in particular is a Two Stroke running a Tec carburetor.

My two cents worth, as always, I appreciate the information and documentation you're providing here. I know you'll stick with it and work it all out. :thumbsup:
 
Sixpac440

Sixpac440

#95
#95
Hi Dave!
I did play with the float level and it didn't change anything.
jaimenv mentioned due to the consistency of 6500 the issue sounds mechanical. That makes sense.

My vision of what's happening here is at 6200 RPM the cam is slinging the valve hard enough to start touching the head, by 6500 RPM its slinging it hard enough that is doesn't have time to fully seat and that's where I'm seeing the gas cloud and the mouth of the carb.
Its possible it came with the wrong keepers, retainers or springs.
Here is a post that talks about the H50 Motorsports valve components.
https://www.smokstak.com/forum/showpost.php?p=720344&postcount=3

If the valves were wrong they just wouldn't fit.
My keepers are not black oxide.
The springs in the pic also look black oxide, mine are not.

When taking the valves out I couldn't just use the valve compressor, the keepers were tight in the retainers, I had to lift the retainer with a screw driver and tap the top of the valve to separate the keeper from the retainer.
Both intake and exhaust side needed that done.
Don't know if that means anything.

I could make up a .100 or whatever shim and put it on the valve for a bit more preload and see if I get an RPM change but if its a keeper issue I could damage parts by adding pressure to the valve stem, tappet and cam lobe.

Any thoughts?

Havasu Dave said:
I can not see where a weak spring allows a valve to open too far Kevin. That is a function of the keepers and gap. From what I understand, the gaps listed in the book are minimum and maximum, not intake and exhaust. Either way, your gaps are good. I agree with you on the valve hitting the head, albeit lightly. I wouldn't contribute it to limiting RPM, because if it was enough to do that, you'd have a bent valve. I would however, attribute it to the noise you hear.

I never did see if you chased fuel level at max. RPM. I have encountered that, with correctly adjusted float levels on hungry, high RPM engines. One in particular is a Two Stroke running a Tec carburetor.

My two cents worth, as always, I appreciate the information and documentation you're providing here. I know you'll stick with it and work it all out. :thumbsup:
Click to expand...
 
ole4

ole4

#96
#96
.100 is too much. Go with a .060 if you have .100 clearance after assembly check for a minimum of .060 between two coils in the middle. after shimming assemble and test again, if rpm changes it will show it is spring related. It is normal for split keepers to get set in the retainer and be hard to disassemble. Do not rev it too high without some kind of load on it. Just see if the rpm changes to a higher rpm or goes away. If it does talk to clements about better springs.
 
Sixpac440

Sixpac440

#98
#98
Dave .. quick thought ...
I don't think its fuel related as it did it with the Tilly too.

I'm a pack rat ... I put the steel retainers in the box the billet ones came in ..
The factory Tecumseh box shows a part # of 36957K .. a Google search show they are billet components for an H50.
 
Sixpac440

Sixpac440

#99
#99
ole4 said:
.100 is too much. Go with a .060 if you have .100 clearance after assembly check for a minimum of .060 between two coils in the middle. after shimming assemble and test again, if rpm changes it will show it is spring related. It is normal for split keepers to get set in the retainer and be hard to disassemble. Do not rev it too high without some kind of load on it. Just see if the rpm changes to a higher rpm or goes away. If it does talk to clements about better springs.
Click to expand...

My concern it that if the valve is touching the head its over extending .100 already.
By adding preload it may cause wear but worse the coils may bind and put pressure in the retainers and keepers.

I called Clements, talked to Kim, she will check stock to see if they have springs (and head gaskets).

If I cant find correct springs I will go off the reservation and do some jury rigging and will try shimming.
I am familiar with coil bind ... it would be checked before firing it up.
Possible some Briggs or Predator hi-RPM springs will work ...
Lets see what Clements has.
 
Sixpac440

Sixpac440

#100
#100
Kim called back ... Mike is not feeling well and I see the business is up for sale.
Echoes of Ron Kimball?

Kim tried to relay my information .... she relayed Mike Clements said the head needed to be milled if the valves are hitting it.
Something was missed in the translation.
Given the information I have I think that is not correct.
Kim said they might have springs and that Mike can look around the shop but it will be awhile. She then said to keep an eye on Face Book for tec motorsports parts they will be putting up for sale.
she was able to sell me 2 head gaskets.
Kim did recommend a face book page to pose questions on ....
 
You must log in or register to reply here.
Top